![Understanding Activities ❘ 35
3
. Add the following statements in bold to the MainActivity.java file:
package net.learn2develop.Dialog;
import android.app.Activity;
import android.os.Bundle;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends Activity {
CharSequence[] items = { “Google”, “Apple”, “Microsoft” };
boolean[] itemsChecked = new boolean [items.length];
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button btn = (Button) findViewById(R.id.btn_dialog);
btn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
showDialog(0);
}
});
}
@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case 0:
return new AlertDialog.Builder(this)
.setIcon(R.drawable.icon)
.setTitle(“This is a dialog with some simple text...”)
.setPositiveButton(“OK”, new
DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int whichButton)
{
Toast.makeText(getBaseContext(),
“OK clicked!”, Toast.LENGTH_SHORT).show();
}
})
.setNegativeButton(“Cancel”, new
DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int whichButton)
{
Toast.makeText(getBaseContext(),
“Cancel clicked!”, Toast.LENGTH_SHORT).show();
}
})](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-57-320.jpg)
![36 ❘ Chapter 2 Activities and Intents
.setMultiChoiceItems(items, itemsChecked, new
DialogInterface.OnMultiChoiceClickListener() {
@Override
public void onClick(DialogInterface dialog, int which,
boolean isChecked) {
Toast.makeText(getBaseContext(),
items[which] + (isChecked ? “ checked!”:
“ unchecked!”),
Toast.LENGTH_SHORT).show();
}
}
)
.create();
}
return null;
}
}
4
. Press F11 to debug the application on the Android Emulator. Click the button to display the dialog
(see Figure 2-6). Checking the various checkboxes will cause the Toast class to display the text of
the item checked/unchecked. To dismiss the dialog, click the OK or Cancel button.
Figure 2-6
How It Works
To display a dialog, you first override the onCreateDialog() method in the Activity class:
@Override
protected Dialog onCreateDialog(int id) {
//...
}](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-58-320.jpg)
![Understanding Activities ❘ 37
This method is called when you call the showDialog() method:
Button btn = (Button) findViewById(R.id.btn_dialog);
btn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
showDialog(0);
}
});
The onCreateDialog() method is a callback for creating dialogs that are managed by the activity. When
you call the showDialog() method, this callback will be invoked. The showDialog() method accepts an
integer argument identifying a particular dialog to display.
To create a dialog, you use the AlertDialog class’s Builder constructor. You set the various properties,
such as icon, title, and buttons, as well as checkboxes:
@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case 0:
return new AlertDialog.Builder(this)
.setIcon(R.drawable.icon)
.setTitle(“This is a dialog with some simple text...”)
.setPositiveButton(“OK”, new
DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int whichButton)
{
Toast.makeText(getBaseContext(),
“OK clicked!”, Toast.LENGTH_SHORT).show();
}
})
.setNegativeButton(“Cancel”, new
DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int whichButton)
{
Toast.makeText(getBaseContext(),
“Cancel clicked!”, Toast.LENGTH_SHORT).show();
}
})
.setMultiChoiceItems(items, itemsChecked, new
DialogInterface.OnMultiChoiceClickListener() {
@Override
public void onClick(DialogInterface dialog, int which,
boolean isChecked) {
Toast.makeText(getBaseContext(),
items[which] + (isChecked ? “ checked!”:
“ unchecked!”),
Toast.LENGTH_SHORT).show();
}
}
)
.create();
}
return null;
}](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-59-320.jpg)
![Understanding Activities ❘ 39
Displaying a Progress Dialog
Besides the plain dialog that you created in the previous section, you can also create a progress dialog.
A progress dialog is useful for showing the progress of some activities, such as the status of a download
operation.
The following Try It Out shows you how to display a progress dialog.
Try It Out Displaying a Progress Dialog Window Using an Activity
1
. Using the same project created in the previous section, add the following statements in bold to the
MainActivity.java file:
package net.learn2develop.Dialog;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import android.app.ProgressDialog;
import android.os.Handler;
import android.os.Message;
public class MainActivity extends Activity {
CharSequence[] items = { “Google”, “Apple”, “Microsoft” };
boolean[] itemsChecked = new boolean [items.length];
private ProgressDialog _progressDialog;
private int _progress = 0;
private Handler _progressHandler;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button btn = (Button) findViewById(R.id.btn_dialog);
btn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
showDialog(1);
_progress = 0;
_progressDialog.setProgress(0);
_progressHandler.sendEmptyMessage(0);
}
});
_progressHandler = new Handler() {](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-61-320.jpg)
![76 ❘ Chapter 2 Activities and Intents
NotificationManager nm = (NotificationManager)
getSystemService(NOTIFICATION_SERVICE);
Notification notif = new Notification(
R.drawable.icon,
“Reminder: Meeting starts in 5 minutes”,
System.currentTimeMillis());
CharSequence from = “System Alarm”;
CharSequence message = “Meeting with customer at 3pm...”;
notif.setLatestEventInfo(this, from, message, pendingIntent);
//---100ms delay, vibrate for 250ms, pause for 100 ms and
// then vibrate for 500ms---
notif.vibrate = new long[] { 100, 250, 100, 500};
nm.notify(notificationID, notif);
}
}
8
. Press F11 to debug the application on the Android Emulator.
9.
Click the Display Notification button (see the top left of Figure 2-27) and a notification will appear
on the status bar.
10.
Clicking and dragging the status bar down will reveal the notification (see the right of Figure 2-27).
11.
Clicking on the notification will reveal the NotificationView activity. This also causes the
notification to be dismissed from the status bar.
Do
Figure 2-27](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-98-320.jpg)
![78 ❘ Chapter 2 Activities and Intents
Next, you set the details of the notification using the setLatestEventInfo() method:
CharSequence from = “System Alarm”;
CharSequence message = “Meeting with customer at 3pm...”;
notif.setLatestEventInfo(this, from, message, pendingIntent);
//---100ms delay, vibrate for 250ms, pause for 100 ms and
// then vibrate for 500ms---
notif.vibrate = new long[] { 100, 250, 100, 500};
The preceding also sets the notification to vibrate the phone. Finally, to display the notification you use
the notify() method:
nm.notify(notificationID, notif);
When the user clicks on the notification, the NotificationView activity is launched. Here, you dismiss
the notification by using the cancel() method of the NotificationManager object and passing it the ID
of the notification (passed in via the Intent object):
//---look up the notification manager service---
NotificationManager nm = (NotificationManager)
getSystemService(NOTIFICATION_SERVICE);
//---cancel the notification that we started
nm.cancel(getIntent().getExtras().getInt(“notificationID”));
Summary
This chapter first provided a detailed look at how activities work and the various forms in which you
can display them. You also learned how to display dialog windows using activities.
The second part of this chapter demonstrated a very important concept in Android — the intent. The
intent is the “glue” that enables different activities to be connected, and is a vital concept to under-
stand when developing for the Android platform.
Exercises
1
. What will happen if you have two or more activities with the same intent filter action name?
2 .
Write the code to invoke the built-in Browser application.
3.
Which components can you specify in an intent filter?
4.
What is the difference between the Toast and NotificationManager class?
Answers to the Exercises can be found in Appendix C.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-100-320.jpg)
![Basic Views ❘ 131
The ImageButton displays a button with an image. The image is set through the src attribute. In this
case, you simply use the image used for the application icon:
<ImageButton android:id=”@+id/btnImg1”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:src=”@drawable/icon” />
The EditText view displays a rectangular region where the user can enter some text. You set the layout
_height to wrap_content so that if the user enters a long string of text, its height will automatically be
adjusted to fit the content (see Figure 4-4).
<EditText android:id=”@+id/txtName”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content” />
Figure 4-4
The CheckBox displays a checkbox that users can tap to check or uncheck it:
<CheckBox android:id=”@+id/chkAutosave”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:text=”Autosave” />
If you do not like the default look of the CheckBox, you can apply a style attribute to it to display it as
some other image, such as a star:
<CheckBox android:id=”@+id/star”
style=”?android:attr/starStyle”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content” />
The format for the value of the style attribute is as follows:
?[package:][type:]name.
The RadioGroup encloses two RadioButtons. This is important because radio buttons are usually used
to present multiple options to the user for selection. When a RadioButton in a RadioGroup is selected, all
other RadioButtons are automatically unselected:
<RadioGroup android:id=”@+id/rdbGp1”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:orientation=”vertical” >
<RadioButton android:id=”@+id/rdb1”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:text=”Option 1” />](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-153-320.jpg)
![142 ❘ Chapter 4 Designing Your User Interface Using Views
android:layout_height=”fill_parent” >
<TextView
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:text=”Name of President” />
<AutoCompleteTextView android:id=”@+id/txtCountries”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content” />
</LinearLayout>
3
. Add the following statements in bold to the MainActivity.java file:
package net.learn2develop.BasicViews3;
import android.app.Activity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
public class MainActivity extends Activity {
String[] presidents = {
“Dwight D. Eisenhower”,
“John F. Kennedy”,
“Lyndon B. Johnson”,
“Richard Nixon”,
“Gerald Ford”,
“Jimmy Carter”,
“Ronald Reagan”,
“George H. W. Bush”,
“Bill Clinton”,
“George W. Bush”,
“Barack Obama”
};
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_dropdown_item_1line, presidents);
AutoCompleteTextView textView = (AutoCompleteTextView)
findViewById(R.id.txtCountries);
textView.setThreshold(3);
textView.setAdapter(adapter);
}
}](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-164-320.jpg)
![Basic Views ❘ 143
4
. Press F11 to debug the application on the Android Emulator. As shown in Figure 4-8, a list of
matching names appears as you type into the AutoCompleteTextView.
Figure 4-8
How It Works
In the MainActivity class, you first create a String array containing a list of presidents’ names:
String[] presidents = {
“Dwight D. Eisenhower”,
“John F. Kennedy”,
“Lyndon B. Johnson”,
“Richard Nixon”,
“Gerald Ford”,
“Jimmy Carter”,
“Ronald Reagan”,
“George H. W. Bush”,
“Bill Clinton”,
“George W. Bush”,
“Barack Obama”
};
The ArrayAdapter object manages the array of strings that will be displayed by the AutoCompleteTextView.
In the preceding example, you set the AutoCompleteTextView to display in the simple_dropdown_item_
1line mode:
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_dropdown_item_1line, presidents);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-165-320.jpg)
![List Views ❘ 157
2
. Modify the MainActivity.java file by inserting the statements shown here in bold:
package net.learn2develop.BasicViews5;
import android.app.Activity;
import android.os.Bundle;
import android.app.ListActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
public class MainActivity extends ListActivity {
String[] presidents = {
“Dwight D. Eisenhower”,
“John F. Kennedy”,
“Lyndon B. Johnson”,
“Richard Nixon”,
“Gerald Ford”,
“Jimmy Carter”,
“Ronald Reagan”,
“George H. W. Bush”,
“Bill Clinton”,
“George W. Bush”,
“Barack Obama”
};
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.main);
setListAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, presidents));
}
public void onListItemClick(
ListView parent, View v, int position, long id)
{
Toast.makeText(this,
“You have selected “ + presidents[position],
Toast.LENGTH_SHORT).show();
}
}
3
. Press F11 to debug the application on the Android Emulator. Figure 4-15 shows the activity dis-
playing the list of presidents’ names.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-179-320.jpg)
![List Views ❘ 159
{
Toast.makeText(this,
“You have selected “ + presidents[position],
Toast.LENGTH_SHORT).show();
}
Here, you simply display the name of the president selected using the Toast class.
Customizing the ListView
The ListView is a versatile control that you can further customize. The following Try It Out shows
how you can allow multiple items in the ListView to be selected and how you can enable filtering
support.
Try It Out Customizing the ListView
1
. Using the same project created in the previous section, add the following statements in bold to the
MainActivity.java file:
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView lstView = getListView();
//lstView.setChoiceMode(0); //CHOICE_MODE_NONE
//lstView.setChoiceMode(1); //CHOICE_MODE_SINGLE
lstView.setChoiceMode(2); //CHOICE_MODE_MULTIPLE
lstView.setTextFilterEnabled(true);
setListAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_checked, presidents));
}
public void onListItemClick(
ListView parent, View v, int position, long id)
{
//---toggle the check displayed next to the item---
parent.setItemChecked(position, parent.isItemChecked(position));
Toast.makeText(this,
“You have selected “ + presidents[position],
Toast.LENGTH_SHORT).show();
}
2
. Press F11 to debug the application on the Android Emulator. You can now click on each item to
display the check icon next to it (see Figure 4-16).](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-181-320.jpg)
![162 ❘ Chapter 4 Designing Your User Interface Using Views
2
. Modify the MainActivity.java file as shown in bold:
public class MainActivity extends ListActivity {
String[] presidents;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView lstView = getListView();
//lstView.setChoiceMode(0); //CHOICE_MODE_NONE
//lstView.setChoiceMode(1); //CHOICE_MODE_SINGLE
lstView.setChoiceMode(2); //CHOICE_MODE_MULTIPLE
lstView.setTextFilterEnabled(true);
presidents =
getResources().getStringArray(R.array.presidents_array);
setListAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_checked, presidents));
}
public void onListItemClick(
ListView parent, View v, int position, long id)
{
//...
//...
}
};
3
. Press F11 to debug the application on the Android Emulator. You should see the same list of
names that appeared in the previous Try It Out.
How It Works
With the names now stored in the strings.xml file, you can retrieve it programmatically in this
MainActivity.java file using the getResources() method:
presidents =
getResources().getStringArray(R.array.presidents_array);
In general, you can programmatically retrieve resources bundled with your application using the
getResources() method.
Using the Spinner View
The ListView displays a long list of items in an activity, but sometimes you may want your user
interface to display other views, and hence you do not have the additional space for a full-screen view](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-184-320.jpg)
![164 ❘ Chapter 4 Designing Your User Interface Using Views
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;
public class MainActivity extends Activity {
String[] presidents;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
presidents =
getResources().getStringArray(R.array.presidents_array);
Spinner s1 = (Spinner) findViewById(R.id.spinner1);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, presidents);
s1.setAdapter(adapter);
s1.setOnItemSelectedListener(new OnItemSelectedListener()
{
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1,
int arg2, long arg3)
{
int index = arg0.getSelectedItemPosition();
Toast.makeText(getBaseContext(),
“You have selected item : “ + presidents[index],
Toast.LENGTH_SHORT).show();
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {}
});
}
}
5
. Press F11 to debug the application on the Android Emulator. Click on the SpinnerView and you
will see a pop-up displaying the list of presidents’ names (see Figure 4-18). Clicking on an item will
display a message showing you the item selected.
How It Works
The preceding example works very much like the ListView. One additional method you need to implement
is the onNothingSelected() method. This method is fired when the user presses the Back button, which
dismisses the list of items displayed. In this case, nothing is selected and you do not need to do anything.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-186-320.jpg)
![172 ❘ Chapter 5 Displaying Pictures and Menus with Views
Figure 5-3 Figure 5-4
7
. Add the following statements in bold to the MainActivity.java file:
package net.learn2develop.Gallery;
import android.app.Activity;
import android.os.Bundle;
import android.content.Context;
import android.content.res.TypedArray;
Do
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.Toast;
public class MainActivity extends Activity {
//---the images to display---
Integer[] imageIDs = {
R.drawable.pic1,
R.drawable.pic2,
R.drawable.pic3,
R.drawable.pic4,
R.drawable.pic5,
R.drawable.pic6,
R.drawable.pic7
};
/** Called when the activity is first created. */
@Override](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-194-320.jpg)
![Using Image Views to Display Pictures ❘ 173
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Gallery gallery = (Gallery) findViewById(R.id.gallery1);
gallery.setAdapter(new ImageAdapter(this));
gallery.setOnItemClickListener(new OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent, View v,
int position, long id)
{
Toast.makeText(getBaseContext(),
“pic” + (position + 1) + “ selected”,
Toast.LENGTH_SHORT).show();
}
});
}
public class ImageAdapter extends BaseAdapter
{
private Context context;
private int itemBackground;
public ImageAdapter(Context c)
{
context = c;
//---setting the style---
TypedArray a = obtainStyledAttributes(R.styleable.Gallery1);
itemBackground = a.getResourceId(
R.styleable.Gallery1_android_galleryItemBackground, 0);
a.recycle();
}
//---returns the number of images---
public int getCount() {
return imageIDs.length;
}
//---returns the ID of an item---
public Object getItem(int position) {
return position;
}
//---returns the ID of an item---
public long getItemId(int position) {
return position;
}
//---returns an ImageView view---
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView = new ImageView(context);
imageView.setImageResource(imageIDs[position]);
imageView.setScaleType(ImageView.ScaleType.FIT_XY);
imageView.setLayoutParams(new Gallery.LayoutParams(150, 120));
imageView.setBackgroundResource(itemBackground);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-195-320.jpg)
![Using Image Views to Display Pictures ❘ 175
1
0. To display the selected image in the ImageView, add the following statements in bold to the
MainActivity.java file:
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Gallery gallery = (Gallery) findViewById(R.id.gallery1);
gallery.setAdapter(new ImageAdapter(this));
gallery.setOnItemClickListener(new OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent, View v,
int position, long id)
{
Toast.makeText(getBaseContext(),
“pic” + (position + 1) + “ selected”,
Toast.LENGTH_SHORT).show();
//---display the images selected---
ImageView imageView = (ImageView) findViewById(R.id.image1);
imageView.setImageResource(imageIDs[position]);
}
});
}
1
1. Press F11 to debug the application again. This time, you will see the image selected in the ImageView
(see Figure 5-7).
Figure 5-7](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-197-320.jpg)
![176 ❘ Chapter 5 Displaying Pictures and Menus with Views
How It Works
You first add the Gallery and ImageView views to main.xml:
<Gallery
android:id=”@+id/gallery1”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content” />
<ImageView
android:id=”@+id/image1”
android:layout_width=”320px”
android:layout_height=”250px”
android:scaleType=”fitXY” />
As mentioned earlier, the Gallery view is used to display the series of images in a horizontal scrolling
list. The ImageView is used to display the image selected by the user.
The list of images to be displayed is stored in the imageIDs array:
//---the images to display---
Integer[] imageIDs = {
R.drawable.pic1,
R.drawable.pic2,
R.drawable.pic3,
R.drawable.pic4,
R.drawable.pic5,
R.drawable.pic6,
R.drawable.pic7
};
You create the ImageAdapter class (which extends the BaseAdapter class) so that it can bind to the
Gallery view with a series of ImageView views:
Gallery gallery = (Gallery) findViewById(R.id.gallery1);
gallery.setAdapter(new ImageAdapter(this));
gallery.setOnItemClickListener(new OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent, View v,
int position, long id)
{
Toast.makeText(getBaseContext(),
“pic” + (position + 1) + “ selected”,
Toast.LENGTH_SHORT).show();
//---display the images selected---
ImageView imageView = (ImageView) findViewById(R.id.image1);
imageView.setImageResource(imageIDs[position]);
}
});
When an image in the Gallery view is selected (i.e., clicked), the position (0 for the first image, 1 for the
second image, and so on) of the selected image is displayed and the image is displayed in the ImageView.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-198-320.jpg)
![178 ❘ Chapter 5 Displaying Pictures and Menus with Views
6
. Add the following bold statements to the MainActivity.java file:
package net.learn2develop.ImageSwitcher;
import android.app.Activity;
import android.os.Bundle;
import android.content.Context;
import android.content.res.TypedArray;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewGroup.LayoutParams;
import android.view.animation.AnimationUtils;
import android.widget.BaseAdapter;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Gallery;
import android.widget.ViewSwitcher.ViewFactory;
import android.widget.ImageSwitcher;
import android.widget.ImageView;
public class MainActivity extends Activity implements ViewFactory {
//---the images to display---
Integer[] imageIDs = {
R.drawable.pic1,
R.drawable.pic2,
R.drawable.pic3,
R.drawable.pic4,
R.drawable.pic5,
R.drawable.pic6,
R.drawable.pic7
};
private ImageSwitcher imageSwitcher;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
imageSwitcher = (ImageSwitcher) findViewById(R.id.switcher1);
imageSwitcher.setFactory(this);
imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this,
android.R.anim.fade_in));
imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this,
android.R.anim.fade_out));
Gallery gallery = (Gallery) findViewById(R.id.gallery1);
gallery.setAdapter(new ImageAdapter(this));
gallery.setOnItemClickListener(new OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent,
View v, int position, long id)
{
imageSwitcher.setImageResource(imageIDs[position]);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-200-320.jpg)
![Using Image Views to Display Pictures ❘ 179
}
});
}
public View makeView()
{
ImageView imageView = new ImageView(this);
imageView.setBackgroundColor(0xFF000000);
imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
imageView.setLayoutParams(new
ImageSwitcher.LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.FILL_PARENT));
return imageView;
}
public class ImageAdapter extends BaseAdapter
{
private Context context;
private int itemBackground;
public ImageAdapter(Context c)
{
context = c;
//---setting the style---
TypedArray a = obtainStyledAttributes(R.styleable.Gallery1);
itemBackground = a.getResourceId(
R.styleable.Gallery1_android_galleryItemBackground, 0);
a.recycle();
}
//---returns the number of images---
public int getCount()
{
return imageIDs.length;
}
//---returns the ID of an item---
public Object getItem(int position)
{
return position;
}
public long getItemId(int position)
{
return position;
}
//---returns an ImageView view---
public View getView(int position, View convertView, ViewGroup parent)
{
ImageView imageView = new ImageView(context);
imageView.setImageResource(imageIDs[position]);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-201-320.jpg)
![Using Image Views to Display Pictures ❘ 181
This method creates a new View to be added in the ImageSwitcher view.
Like the Gallery example in the previous section, you also implemented an ImageAdapter class so that
it can bind to the Gallery view with a series of ImageView views.
In the onCreate() method, you get a reference to the ImageSwitcher view and set the animation, specify-
ing how images should “fly” in and out of the view. Finally, when an image is selected from the Gallery
view, the image is displayed in the ImageSwitcher view:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
imageSwitcher = (ImageSwitcher) findViewById(R.id.switcher1);
imageSwitcher.setFactory(this);
imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this,
android.R.anim.fade_in));
imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this,
android.R.anim.fade_out));
Gallery gallery = (Gallery) findViewById(R.id.gallery1);
gallery.setAdapter(new ImageAdapter(this));
gallery.setOnItemClickListener(new OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent,
View v, int position, long id)
{
imageSwitcher.setImageResource(imageIDs[position]);
}
});
}
In this example, when an image is selected in the Gallery view, it will appear by “fading” in. When the
next image is selected, the current image will fade out. If you want the image to slide in from the left and
slide out to the right when another image is selected, try the following animation:
imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this,
android.R.anim.slide_in_left));
imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this,
android.R.anim.slide_out_right));
Like the previous Try It Out, you also created the ImageAdapter class (which extends the BaseAdapter
class) so that it can bind to the Gallery view with a series of ImageView views.
GridView
The GridView shows items in a two-dimensional scrolling grid. You can use the GridView together
with an ImageView to display a series of images. The following Try It Out demonstrates how.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-203-320.jpg)
![Using Image Views to Display Pictures ❘ 183
//---the images to display---
Integer[] imageIDs = {
R.drawable.pic1,
R.drawable.pic2,
R.drawable.pic3,
R.drawable.pic4,
R.drawable.pic5,
R.drawable.pic6,
R.drawable.pic7
};
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
GridView gridView = (GridView) findViewById(R.id.gridview);
gridView.setAdapter(new ImageAdapter(this));
gridView.setOnItemClickListener(new OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent,
View v, int position, long id)
{
Toast.makeText(getBaseContext(),
“pic” + (position + 1) + “ selected”,
Toast.LENGTH_SHORT).show();
}
});
}
public class ImageAdapter extends BaseAdapter
{
private Context context;
public ImageAdapter(Context c)
{
context = c;
}
//---returns the number of images---
public int getCount() {
return imageIDs.length;
}
//---returns the ID of an item---
public Object getItem(int position) {
return position;
}
//---returns the ID of an item---
public long getItemId(int position) {
return position;
}
//---returns an ImageView view---
public View getView(int position, View convertView,](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-205-320.jpg)
![184 ❘ Chapter 5 Displaying Pictures and Menus with Views
ViewGroup parent)
{
ImageView imageView;
if (convertView == null) {
imageView = new ImageView(context);
imageView.setLayoutParams(new
GridView.LayoutParams(85, 85));
imageView.setScaleType(
ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(5, 5, 5, 5);
} else {
imageView = (ImageView) convertView;
}
imageView.setImageResource(imageIDs[position]);
return imageView;
}
}
}
5
. Press F11 to debug the application on the Android Emulator. Figure 5-10 shows the GridView
displaying all the images.
Figure 5-10
How It Works
Like the Gallery and ImageSwitcher example, you implement the ImageAdapter class and then bind it
to the GridView:
GridView gridView = (GridView) findViewById(R.id.gridview);
gridView.setAdapter(new ImageAdapter(this));
gridView.setOnItemClickListener(new OnItemClickListener()](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-206-320.jpg)
![Using Menus with Views ❘ 185
{
public void onItemClick(AdapterView<?> parent,
View v, int position, long id)
{
Toast.makeText(getBaseContext(),
“pic” + (position + 1) + “ selected”,
Toast.LENGTH_SHORT).show();
}
});
When an image is selected, you display a Toast message indicating the image selected.
Within the GridView, you can specify the size of the images and how images are spaced out in the
GridView by setting the padding for each image:
//---returns an ImageView view---
public View getView(int position, View convertView,
ViewGroup parent)
{
ImageView imageView;
if (convertView == null) {
imageView = new ImageView(context);
imageView.setLayoutParams(new
GridView.LayoutParams(85, 85));
imageView.setScaleType(
ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(5, 5, 5, 5);
} else {
imageView = (ImageView) convertView;
}
imageView.setImageResource(imageIDs[position]);
return imageView;
}
Using Menus with Views
Menus are useful for displaying additional options that are not directly visible on the main UI of an
application. There are two main types of menus in Android:
➤➤ Options menu — Displays information related to the current activity. In Android, you activate
the options menu by pressing the MENU key.
➤➤ Context menu — Displays information related to a particular view on an activity. In Android,
to activate a context menu you tap and hold on to it.
Figure 5-11 shows an example of an options menu in the browser application. The option menu is
displayed whenever the user presses the MENU button. The menu items displayed vary according to
the current activity that is running.
Figure 5-12 shows a context menu that is displayed when the user presses and holds on a hyperlink
displayed on the page. The menu items displayed vary according to the component or view currently
selected. To activate the context menu, the user selects an item on the screen and either taps and
holds it or simply presses the center button on the directional keypad.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-207-320.jpg)
![Persisting Data to Files ❘ 211
Button saveBtn = (Button) findViewById(R.id.btnSave);
Button loadBtn = (Button) findViewById(R.id.btnLoad);
saveBtn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String str = textBox.getText().toString();
try
{
FileOutputStream fOut =
openFileOutput(“textfile.txt”,
MODE_WORLD_READABLE);
OutputStreamWriter osw = new
OutputStreamWriter(fOut);
//---write the string to the file---
osw.write(str);
osw.flush();
osw.close();
//---display file saved message---
Toast.makeText(getBaseContext(),
“File saved successfully!”,
Toast.LENGTH_SHORT).show();
//---clears the EditText---
textBox.setText(“”);
}
catch (IOException ioe)
{
ioe.printStackTrace();
}
}
});
loadBtn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
try
{
FileInputStream fIn =
openFileInput(“textfile.txt”);
InputStreamReader isr = new
InputStreamReader(fIn);
char[] inputBuffer = new char[READ_BLOCK_SIZE];
String s = “”;
int charRead;
while ((charRead = isr.read(inputBuffer))>0)
{
//---convert the chars to a String---
String readString =
String.copyValueOf(inputBuffer, 0,
charRead);
s += readString;
inputBuffer = new char[READ_BLOCK_SIZE];](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-233-320.jpg)
![Persisting Data to Files ❘ 213
How It Works
To save text into a file, you use the FileOutputStream class. The openFileOutput() method opens a
named file for writing, with the mode specified. In this example, you use the MODE_WORLD_READABLE
constant to indicate that the file is readable by all other applications:
FileOutputStream fOut =
openFileOutput(“textfile.txt”,
MODE_WORLD_READABLE);
Apart from the MODE_WORLD_READABLE constant, you can select from the following: MODE_PRIVATE (file
can only be accessed by the application that created it), MODE_APPEND (for appending to an existing file),
and MODE_WORLD_WRITEABLE (all other applications have write access to the file).
To convert a character stream into a byte stream, you use an instance of the OutputStreamWriter class,
by passing it an instance of the FileOutputStream object:
OutputStreamWriter osw = new
OutputStreamWriter(fOut);
You then use its write() method to write the string to the file. To ensure that all the bytes are written
to the file, use the flush() method. Finally, use the close() method to close the file:
osw.write(str);
osw.flush();
osw.close();
To read the content of a file, you use the FileInputStream class, together with the InputStreamReader class:
FileInputStream fIn =
openFileInput(“textfile.txt”);
InputStreamReader isr = new
InputStreamReader(fIn);
As you do not know the size of the file to read, the content is read in blocks of 100 characters into a
buffer (character array). The characters read are then copied into a String object:
char[] inputBuffer = new char[READ_BLOCK_SIZE];
String s = “”;
int charRead;
while ((charRead = isr.read(inputBuffer))>0)
{
//---convert the chars to a String---
String readString =
String.copyValueOf(inputBuffer, 0,
charRead);
s += readString;
inputBuffer = new char[READ_BLOCK_SIZE];
}
The read() method of the InputStreamReader object reads the number of characters read and returns -1
if the end of the file is reached.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-235-320.jpg)
![Persisting Data to Files ❘ 215
osw.close();
//---display file saved message---
Toast.makeText(getBaseContext(),
“File saved successfully!”,
Toast.LENGTH_SHORT).show();
//---clears the EditText---
textBox.setText(“”);
}
catch (IOException ioe)
{
ioe.printStackTrace();
}
}
});
The preceding code uses the getExternalStorageDirectory() method to return the full path to the
external storage. Typically, it should return the “/sdcard” path for a real device, and “/mnt/sdcard”
for an Android Emulator. However, you should never try to hardcode the path to the SD card, as
manufacturers may choose to assign a different path name to the SD card. Hence, be sure to use the
getExternalStorageDirectory() method to return the full path to the SD card.
You then create a directory called MyFiles in the SD card. Finally, you save the file into this
directory.
To load the file from the external storage, modify the onClick() method for the Load button:
loadBtn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
try
{
//---SD Storage---
File sdCard = Environment.getExternalStorageDirectory();
File directory = new File (sdCard.getAbsolutePath() +
“/MyFiles”);
File file = new File(directory, “textfile.txt”);
FileInputStream fIn = new FileInputStream(file);
InputStreamReader isr = new InputStreamReader(fIn);
char[] inputBuffer = new char[READ_BLOCK_SIZE];
String s = “”;
int charRead;
while ((charRead = isr.read(inputBuffer))>0)
{
//---convert the chars to a String---
String readString =
String.copyValueOf(inputBuffer, 0, charRead);
s += readString;
inputBuffer = new char[READ_BLOCK_SIZE];
}
//---set the EditText to the text that has been
// read---](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-237-320.jpg)
![220 ❘ Chapter 6 Data Persistence
onCreate(db);
}
}
//---opens the database---
public DBAdapter open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}
//---closes the database---
public void close()
{
DBHelper.close();
}
//---insert a contact into the database---
public long insertContact(String name, String email)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_NAME, name);
initialValues.put(KEY_EMAIL, email);
return db.insert(DATABASE_TABLE, null, initialValues);
}
//---deletes a particular contact---
public boolean deleteContact(long rowId)
{
return db.delete(DATABASE_TABLE, KEY_ROWID + “=” + rowId, null) > 0;
}
//---retrieves all the contacts---
public Cursor getAllContacts()
{
return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME,
KEY_EMAIL}, null, null, null, null, null);
}
//---retrieves a particular contact---
public Cursor getContact(long rowId) throws SQLException
{
Cursor mCursor =
db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
KEY_NAME, KEY_EMAIL}, KEY_ROWID + “=” + rowId, null,
null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
//---updates a contact---
public boolean updateContact(long rowId, String name, String email)](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-242-320.jpg)
![Creating and Using Databases ❘ 223
DBHelper.close();
}
//---insert a contact into the database---
public long insertContact(String name, String email)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_NAME, name);
initialValues.put(KEY_EMAIL, email);
return db.insert(DATABASE_TABLE, null, initialValues);
}
//---deletes a particular contact---
public boolean deleteContact(long rowId)
{
return db.delete(DATABASE_TABLE, KEY_ROWID + “=” + rowId, null) > 0;
}
//---retrieves all the contacts---
public Cursor getAllContacts()
{
return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME,
KEY_EMAIL}, null, null, null, null, null);
}
//---retrieves a particular contact---
public Cursor getContact(long rowId) throws SQLException
{
Cursor mCursor =
db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
KEY_NAME, KEY_EMAIL}, KEY_ROWID + “=” + rowId, null,
null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
//---updates a contact---
public boolean updateContact(long rowId, String name, String email)
{
ContentValues args = new ContentValues();
args.put(KEY_NAME, name);
args.put(KEY_EMAIL, email);
return db.update(DATABASE_TABLE, args, KEY_ROWID + “=” + rowId, null) > 0;
}
}
Notice that Android uses the Cursor class as a return value for queries. Think of the Cursor as a pointer
to the result set from a database query. Using Cursor enables Android to more efficiently manage rows
and columns as needed.
You use a ContentValues object to store key/value pairs. Its put() method enables you to insert keys
with values of different data types.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-245-320.jpg)
![232 ❘ Chapter 6 Data Persistence
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
try {
String destPath = “/data/data/” + getPackageName() +
“/databases/MyDB”;
File f = new File(destPath);
if (!f.exists()) {
CopyDB( getBaseContext().getAssets().open(“mydb”),
new FileOutputStream(destPath));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
DBAdapter db = new DBAdapter(this);
//---get all contacts---
db.open();
Cursor c = db.getAllContacts();
if (c.moveToFirst())
{
do {
DisplayContact(c);
} while (c.moveToNext());
}
db.close();
}
public void CopyDB(InputStream inputStream,
OutputStream outputStream)
throws IOException {
//---copy 1K bytes at a time---
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer)) > 0) {
outputStream.write(buffer, 0, length);
}
inputStream.close();
outputStream.close();
}
3
. Press F11 to debug the application on the Android Emulator. When the application runs, it will
copy the mydb database file into the /data/data/net.learn2develop.Databases/databases/ folder
with the name MyDB.
How It Works
You first defined the CopyDB() method to copy the database file from one location to another:
public void CopyDB(InputStream inputStream,](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-254-320.jpg)
![Creating and Using Databases ❘ 233
OutputStream outputStream)
throws IOException {
//---copy 1K bytes at a time---
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer)) > 0) {
outputStream.write(buffer, 0, length);
}
inputStream.close();
outputStream.close();
}
Note that in this case you used the InputStream object to read from the source file, and then wrote it to
the destination file using the OutputStream object.
When the activity is created, you copy the database file located in the assets folder into the /data/data/
net.learn2develop.Databases/databases/ folder on the Android device (or emulator):
try {
String destPath = “/data/data/” + getPackageName() +
“/databases/MyDB”;
File f = new File(destPath);
if (!f.exists()) {
CopyDB( getBaseContext().getAssets().open(“mydb”),
new FileOutputStream(destPath));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
You copy the database file only if it does not exist in the destination folder. If you don’t perform this
check, every time the activity is created you will overwrite the database file with the one in the assets
folder. This may not be desirable, as your application may make changes to the database file during
run time, and this will wipe out all the changes you have made so far.
To ensure that the database file is indeed copied, be sure to delete the database file in your emulator (if it
already existed) prior to testing the application. You can delete the database using DDMS (see Figure 6-16).
Figure 6-16](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-255-320.jpg)
![240 ❘ Chapter 7 Content Providers
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:layout_weight=”1”
android:stackFromBottom=”false”
android:transcriptMode=”normal”
/>
<TextView
android:id=”@+id/contactName”
android:textStyle=”bold”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
/>
<TextView
android:id=”@+id/contactID”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
/>
</LinearLayout>
3
. In the MainActivity.java class, code the following:
package net.learn2develop.Provider;
import android.app.Activity;
import android.os.Bundle;
import android.app.ListActivity;
import android.database.Cursor;
import android.net.Uri;
import android.provider.ContactsContract;
import android.widget.SimpleCursorAdapter;
public class MainActivity extends ListActivity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Uri allContacts = Uri.parse(“content://contacts/people”);
Cursor c = managedQuery(allContacts, null, null, null, null);
String[] columns = new String[] {
ContactsContract.Contacts.DISPLAY_NAME,
ContactsContract.Contacts._ID};
int[] views = new int[] {R.id.contactName, R.id.contactID};
SimpleCursorAdapter adapter =
new SimpleCursorAdapter(this, R.layout.main, c, columns, views);
this.setListAdapter(adapter);
}
}](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-262-320.jpg)
![242 ❘ Chapter 7 Content Providers
Figure 7-3
How It Works
In this example, you retrieved all the contacts stored in the Contacts application and displayed them in
the ListView.
The managedQuery() method of the Activity class retrieves a managed cursor. A managed cursor
handles all the work of unloading itself when the application pauses and requerying itself when the
application restarts.
The statement
Cursor c = managedQuery(allContacts, null, null, null, null);
is equivalent to
Cursor c = getContentResolver().query(allContacts, null, null, null, null);
startManagingCursor(c); //---allows the activity to manage the Cursor’s
// lifecyle based on the activity’s lifecycle---
The getContentResolver() method returns a ContentResolver object, which helps to resolve a content
URI with the appropriate content provider.
The SimpleCursorAdapter object maps a cursor to TextViews (or ImageViews) defined in your XML file
(main.xml). It maps the data (as represented by columns) to views (as represented by views):
String[] columns = new String[] {
ContactsContract.Contacts.DISPLAY_NAME,
ContactsContract.Contacts._ID};](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-264-320.jpg)
![Using a Content Provider ❘ 243
int[]views=newint[]{R.id.contactName,R.id.contactID};
SimpleCursorAdapteradapter=
newSimpleCursorAdapter(this,R.layout.main,c,columns,views);
this.setListAdapter(adapter);
Note that in order for your application to access the Contacts application, you need to have the READ_
CONTACTS permission in your AndroidManifest.xml fi le.
predefined Query String constants
Besides using the query URI, you can use a list of predefined query string constants in Android to specify
the URI for the different data types. For example, besides using the query content://contacts/people,
you can rewrite the following statement
UriallContacts=Uri.parse(“content://contacts/people”);
using one of the predefi ned constants in Android, as
UriallContacts=ContactsContract.Contacts.CONTENT_URI;
NOTE For Android 2.0 and later, to query the base Contacts records you need
to use the ContactsContract.Contacts.CONTENT_URI URI.
Some examples of predefi ned query string constants are as follows:
➤➤ Browser.BOOKMARKS_URI
➤➤ Browser.SEARCHES_URI
➤➤ CallLog.CONTENT_URI
➤➤ MediaStore.Images.Media.INTERNAL_CONTENT_URI
➤➤ MediaStore.Images.Media.EXTERNAL_CONTENT_URI
➤➤ Settings.CONTENT_URI
If you want to retrieve the fi rst contact, specify the ID of that contact, like this:
UrioneContact=Uri.parse(“content://contacts/people/1”);
Alternatively, use the predefi ned constant together with the withAppendedId() method of the
ContentUris class:
importandroid.content.ContentUris;
//...
UrioneContact=ContentUris.withAppendedId(
ContactsContract.Contacts.CONTENT_URI,1);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-265-320.jpg)
![244 ❘ Chapter 7 Content Providers
Besides binding to a ListView, you can also print out the results using the Cursor object, as shown here:
package net.learn2develop.Provider;
import android.app.Activity;
import android.os.Bundle;
import android.app.ListActivity;
import android.database.Cursor;
import android.net.Uri;
import android.provider.ContactsContract;
import android.widget.SimpleCursorAdapter;
import android.util.Log;
public class MainActivity extends ListActivity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Uri allContacts = ContactsContract.Contacts.CONTENT_URI;
Cursor c = managedQuery(
allContacts, null, null, null, null);
String[] columns = new String[] {
ContactsContract.Contacts.DISPLAY_NAME,
ContactsContract.Contacts._ID};
int[] views = new int[] {R.id.contactName, R.id.contactID};
SimpleCursorAdapter adapter =
new SimpleCursorAdapter(this, R.layout.main,
c, columns, views);
this.setListAdapter(adapter);
PrintContacts(c);
}
private void PrintContacts(Cursor c)
{
if (c.moveToFirst()) {
do{
String contactID = c.getString(c.getColumnIndex(
ContactsContract.Contacts._ID));
String contactDisplayName =
c.getString(c.getColumnIndex(
ContactsContract.Contacts.DISPLAY_NAME));
Log.v(“Content Providers”, contactID + “, “ +
contactDisplayName);
} while (c.moveToNext());
}
}
}](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-266-320.jpg)
![246 ❘ chApter 7 content ProviderS
NOTE To access the phone number of a contact, you need to query against the
URI stored in ContactsContract.CommonDataKinds.Phone.CONTENT_URI.
In the preceding code snippet, you fi rst check whether a contact has a phone number using the
ContactsContract.Contacts.HAS_PHONE_NUMBER field. If the contact has at least a phone number,
you then query the content provider again based on the ID of the contact. Once the phone number(s)
are retrieved, you then iterate through them and print out the numbers. You should see something
like this:
12-1302:41:09.541:VERBOSE/ContentProviders(546):
1,Wei-MengLee
12-1302:41:09.541:VERBOSE/ContentProviders(546):
969-240-65
12-1302:41:09.541:VERBOSE/ContentProviders(546):
2,SallyJackson
12-1302:41:09.541:VERBOSE/ContentProviders(546):
345-668-43
projections
The second parameter of the managedQuery() method controls how many columns are returned by
the query; this parameter is known as the projection. Earlier, you specified null:
Cursorc=managedQuery(allContacts,
null,null,null,null);
You can specify the exact columns to return by creating an array containing the name of the column
to return, like this:
String[]projection=newString[]
{ContactsContract.Contacts._ID,
ContactsContract.Contacts.DISPLAY_NAME,
ContactsContract.Contacts.HAS_PHONE_NUMBER};
Cursorc=managedQuery(allContacts,projection,
null,null,null);
In the above case, the _ID, DISPLAY_NAME, and HAS_PHONE_NUMBER fields will be retrieved.
Filtering
The third and fourth parameters of the managedQuery() method enable you to specify a SQL WHERE
clause to fi lter the result of the query. For example, the following statement retrieves only the people
whose name ends with “Lee”:
Cursorc=managedQuery(allContacts,projection,
ContactsContract.Contacts.DISPLAY_NAME+“LIKE‘%Lee’”,
null,null);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-268-320.jpg)
![Creating Your Own Content Providers ❘ 247
Here, the third parameter contains a SQL statement containing the name to search for (“Lee”). You
can also put the search string into the fourth argument of the method, like this:
Cursor c = managedQuery(allContacts, projection,
ContactsContract.Contacts.DISPLAY_NAME + “ LIKE ?”,
new String[] {“%Lee”} , null);
Sorting
The fifth parameter of the managedQuery() method enables you to specify a SQL ORDER BY clause to
sort the result of the query. For example, the following statement sorts the contact names in ascend-
ing order:
Cursor c = managedQuery(
allContacts,
projection,
ContactsContract.Contacts.DISPLAY_NAME + “ LIKE ?”,
new String[] {“%”} ,
ContactsContract.Contacts.DISPLAY_NAME + “ ASC”);
To sort in descending order, use the DESC keyword:
Cursor c = managedQuery(
allContacts,
projection,
ContactsContract.Contacts.DISPLAY_NAME + “ LIKE ?”,
new String[] {“%”} ,
ContactsContract.Contacts.DISPLAY_NAME + “ DESC”);
Creating Your Own Content Providers
Creating your own content provider in Android is pretty simple.
All you need to do is extend the abstract ContentProvider class
and override the various methods defined within it.
In this section, you will learn how to create a simple content pro-
vider that stores a list of books. For ease of illustration, the content
provider stores the books in a database table containing three fields,
as shown in Figure 7-4. Figure 7-4
The following Try It Out shows you the steps.
Try It Out Creating Your Own Content Provider
codefile ContentProviders.zip available for download at Wrox.com
1
. Using Eclipse, create a new Android project and name it as ContentProviders.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-269-320.jpg)
![Creating Your Own Content Providers ❘ 249
private static final String DATABASE_NAME = “Books”;
private static final String DATABASE_TABLE = “titles”;
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE =
“create table “ + DATABASE_TABLE +
“ (_id integer primary key autoincrement, “
+ “title text not null, isbn text not null);”;
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
db.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion) {
Log.w(“Content provider database”,
“Upgrading database from version “ +
oldVersion + “ to “ + newVersion +
“, which will destroy all old data”);
db.execSQL(“DROP TABLE IF EXISTS titles”);
onCreate(db);
}
}
@Override
public int delete(Uri arg0, String arg1, String[] arg2) {
// arg0 = uri
// arg1 = selection
// arg2 = selectionArgs
int count=0;
switch (uriMatcher.match(arg0)){
case BOOKS:
count = booksDB.delete(
DATABASE_TABLE,
arg1,
arg2);
break;
case BOOK_ID:
String id = arg0.getPathSegments().get(1);
count = booksDB.delete(
DATABASE_TABLE,
_ID + “ = “ + id +
(!TextUtils.isEmpty(arg1) ? “ AND (“ +
arg1 + ‘)’ : “”),
arg2);
break;
default: throw new IllegalArgumentException(“Unknown URI “ + arg0);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-271-320.jpg)
![250 ❘ Chapter 7 Content Providers
}
getContext().getContentResolver().notifyChange(arg0, null);
return count;
}
@Override
public String getType(Uri uri) {
switch (uriMatcher.match(uri)){
//---get all books---
case BOOKS:
return “vnd.android.cursor.dir/vnd.learn2develop.books “;
//---get a particular book---
case BOOK_ID:
return “vnd.android.cursor.item/vnd.learn2develop.books “;
default:
throw new IllegalArgumentException(“Unsupported URI: “ + uri);
}
}
@Override
public Uri insert(Uri uri, ContentValues values) {
//---add a new book---
long rowID = booksDB.insert(
DATABASE_TABLE,
“”,
values);
//---if added successfully---
if (rowID>0)
{
Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
getContext().getContentResolver().notifyChange(_uri, null);
return _uri;
}
throw new SQLException(“Failed to insert row into “ + uri);
}
@Override
public boolean onCreate() {
Context context = getContext();
DatabaseHelper dbHelper = new DatabaseHelper(context);
booksDB = dbHelper.getWritableDatabase();
return (booksDB == null)? false:true;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder sqlBuilder = new SQLiteQueryBuilder();
sqlBuilder.setTables(DATABASE_TABLE);
if (uriMatcher.match(uri) == BOOK_ID)
//---if getting a particular book---
sqlBuilder.appendWhere(](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-272-320.jpg)
![Creating Your Own Content Providers ❘ 251
_ID + “ = “ + uri.getPathSegments().get(1));
if (sortOrder==null || sortOrder==””)
sortOrder = TITLE;
Cursor c = sqlBuilder.query(
booksDB,
projection,
selection,
selectionArgs,
null,
null,
sortOrder);
//---register to watch a content URI for changes---
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
int count = 0;
switch (uriMatcher.match(uri)){
case BOOKS:
count = booksDB.update(
DATABASE_TABLE,
values,
selection,
selectionArgs);
break;
case BOOK_ID:
count = booksDB.update(
DATABASE_TABLE,
values,
_ID + “ = “ + uri.getPathSegments().get(1) +
(!TextUtils.isEmpty(selection) ? “ AND (“ +
selection + ‘)’ : “”),
selectionArgs);
break;
default: throw new IllegalArgumentException(“Unknown URI “ + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
}
4
. Add the following statements in bold to the AndroidManifest.xml file:
<?xml version=”1.0” encoding=”utf-8”?>
<manifest xmlns:android=”http://schemas.android.com/apk/res/android”
package=”net.learn2develop.ContentProviders”
android:versionCode=”1”
android:versionName=”1.0”>
<application android:icon=”@drawable/icon” android:label=”@string/app_name”>](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-273-320.jpg)
![254 ❘ Chapter 7 Content Providers
Next, you override the onCreate() method to open a connection to the database when the content
provider is started:
@Override
public boolean onCreate() {
Context context = getContext();
DatabaseHelper dbHelper = new DatabaseHelper(context);
booksDB = dbHelper.getWritableDatabase();
return (booksDB == null)? false:true;
}
You override the query() method to allow clients to query for books:
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder sqlBuilder = new SQLiteQueryBuilder();
sqlBuilder.setTables(DATABASE_TABLE);
if (uriMatcher.match(uri) == BOOK_ID)
//---if getting a particular book---
sqlBuilder.appendWhere(
_ID + “ = “ + uri.getPathSegments().get(1));
if (sortOrder==null || sortOrder==””)
sortOrder = TITLE;
Cursor c = sqlBuilder.query(
booksDB,
projection,
selection,
selectionArgs,
null,
null,
sortOrder);
//---register to watch a content URI for changes---
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}
By default, the result of the query is sorted using the title field. The resulting query is returned as a
Cursor object.
To allow a new book to be inserted into the content provider, override the insert() method:
@Override
public Uri insert(Uri uri, ContentValues values) {
//---add a new book---
long rowID = booksDB.insert(
DATABASE_TABLE,
“”,
values);
//---if added successfully---
if (rowID>0)](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-276-320.jpg)
![Creating Your Own Content Providers ❘ 255
{
Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
getContext().getContentResolver().notifyChange(_uri, null);
return _uri;
}
throw new SQLException(“Failed to insert row into “ + uri);
}
Once the record is inserted successfully, call the notifyChange() method of the ContentResolver. This
will notify registered observers that a row was updated.
To delete a book, override the delete() method:
public int delete(Uri arg0, String arg1, String[] arg2) {
// arg0 = uri
// arg1 = selection
// arg2 = selectionArgs
int count=0;
switch (uriMatcher.match(arg0)){
case BOOKS:
count = booksDB.delete(
DATABASE_TABLE,
arg1,
arg2);
break;
case BOOK_ID:
String id = arg0.getPathSegments().get(1);
count = booksDB.delete(
DATABASE_TABLE,
_ID + “ = “ + id +
(!TextUtils.isEmpty(arg1) ? “ AND (“ +
arg1 + ‘)’ : “”),
arg2);
break;
default: throw new IllegalArgumentException(“Unknown URI “ + arg0);
}
getContext().getContentResolver().notifyChange(arg0, null);
return count;
}
Likewise, call the notifyChange() method of the ContentResolver after the deletion. This will notify
registered observers that a row was deleted.
Finally, to update a book, override the update() method:
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
int count = 0;
switch (uriMatcher.match(uri)){
case BOOKS:
count = booksDB.update(
DATABASE_TABLE,
values,
selection,
selectionArgs);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-277-320.jpg)
![SMS Messaging ❘ 271
package=”net.learn2develop.SMS”
android:versionCode=”1”
android:versionName=”1.0”>
<application android:icon=”@drawable/icon” android:label=”@string/app_name”>
<activity android:name=”.MainActivity”
android:label=”@string/app_name”>
<intent-filter>
<action android:name=”android.intent.action.MAIN” />
<category android:name=”android.intent.category.LAUNCHER” />
</intent-filter>
</activity>
<receiver android:name=”.SMSReceiver”>
<intent-filter>
<action android:name=
“android.provider.Telephony.SMS_RECEIVED” />
</intent-filter>
</receiver>
</application>
<uses-sdk android:minSdkVersion=”8” />
<uses-permission android:name=”android.permission.SEND_SMS”></uses-permission>
<uses-permission android:name=”android.permission.RECEIVE_SMS”>
</uses-permission>
</manifest>
2
. In the src folder of the project, add a new Class file to the package name
and call it SMSReceiver.java (see Figure 8-4).
3.
Code the SMSReceiver.java file as follows:
package net.learn2develop.SMS;
Figure 8-4
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.telephony.SmsMessage;
import android.widget.Toast;
public class SMSReceiver extends BroadcastReceiver
{
@Override
public void onReceive(Context context, Intent intent)
{
//---get the SMS message passed in---
Bundle bundle = intent.getExtras();
SmsMessage[] msgs = null;
String str = “”;
if (bundle != null)
{
//---retrieve the SMS message received---
Object[] pdus = (Object[]) bundle.get(“pdus”);
msgs = new SmsMessage[pdus.length];
for (int i=0; i<msgs.length; i++){
msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]);
str += “SMS from “ + msgs[i].getOriginatingAddress();](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-293-320.jpg)
![272 ❘ Chapter 8 Messaging and Networking
str += “ :”;
str += msgs[i].getMessageBody().toString();
str += “n”;
}
//---display the new SMS message---
Toast.makeText(context, str, Toast.LENGTH_SHORT).show();
}
}
}
4
. Press F11 to debug the application on the Android Emulator.
5.
Using the DDMS, send a message to the emulator. Your application should be able to receive the
message and display it using the Toast class (see Figure 8-5).
Figure 8-5
How It Works
To listen for incoming SMS messages, you create a BroadcastReceiver class. The BroadcastReceiver
class enables your application to receive intents sent by other applications using the sendBroadcast()
method. Essentially, it enables your application to handle events raised by other applications. When an
intent is received, the onReceive() method is called; hence, you need to override this.
When an incoming SMS message is received, the onReceive() method is fired. The SMS message is
contained in the Intent object (intent; the second parameter in the onReceive() method) via a Bundle
object. The messages are stored in an Object array in the PDU format. To extract each message, you
use the static createFromPdu() method from the SmsMessage class. The SMS message is then displayed
using the Toast class. The phone number of the sender is obtained via the getOriginatingAddress()](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-294-320.jpg)
![274 ❘ Chapter 8 Messaging and Networking
{
@Override
public void onReceive(Context context, Intent intent)
{
//---get the SMS message passed in---
Bundle bundle = intent.getExtras();
SmsMessage[] msgs = null;
String str = “”;
if (bundle != null)
{
//---retrieve the SMS message received---
Object[] pdus = (Object[]) bundle.get(“pdus”);
msgs = new SmsMessage[pdus.length];
for (int i=0; i<msgs.length; i++){
msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]);
str += “SMS from “ + msgs[i].getOriginatingAddress();
str += “ :”;
str += msgs[i].getMessageBody().toString();
str += “n”;
}
//---display the new SMS message---
Toast.makeText(context, str, Toast.LENGTH_SHORT).show();
//---send a broadcast intent to update the SMS received in the activity---
Intent broadcastIntent = new Intent();
broadcastIntent.setAction(“SMS_RECEIVED_ACTION”);
broadcastIntent.putExtra(“sms”, str);
context.sendBroadcast(broadcastIntent);
}
}
}
3
. Add the following statements in bold to the MainActivity.java file:
package net.learn2develop.SMS;
import android.app.Activity;
import android.os.Bundle;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.telephony.SmsManager;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import android.content.BroadcastReceiver;
import android.content.IntentFilter;
import android.widget.TextView;
public class MainActivity extends Activity {
Button btnSendSMS;
IntentFilter intentFilter;
private BroadcastReceiver intentReceiver = new BroadcastReceiver() {](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-296-320.jpg)
![SMS Messaging ❘ 279
//---get the SMS message passed in---
Bundle bundle = intent.getExtras();
SmsMessage[] msgs = null;
String str = “”;
if (bundle != null)
{
//---retrieve the SMS message received---
Object[] pdus = (Object[]) bundle.get(“pdus”);
msgs = new SmsMessage[pdus.length];
for (int i=0; i<msgs.length; i++){
msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]);
str += “SMS from “ + msgs[i].getOriginatingAddress();
str += “ :”;
str += msgs[i].getMessageBody().toString();
str += “n”;
}
//---display the new SMS message---
Toast.makeText(context, str, Toast.LENGTH_SHORT).show();
//---launch the MainActivity---
Intent mainActivityIntent = new Intent(context, MainActivity.class);
mainActivityIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(mainActivityIntent);
//---send a broadcast to update the SMS received in the activity---
Intent broadcastIntent = new Intent();
broadcastIntent.setAction(“SMS_RECEIVED_ACTION”);
broadcastIntent.putExtra(“sms”, str);
context.sendBroadcast(broadcastIntent);
}
}
3
. Modify the main.xml file as follows:
<activity android:name=”.MainActivity”
android:label=”@string/app_name”
android:launchMode=”singleTask” >
<intent-filter>
<action android:name=”android.intent.action.MAIN” />
<category android:name=”android.intent.category.LAUNCHER” />
</intent-filter>
</activity>
4
. Press F11 to debug the application on the Android Emulator. When the MainActivity is shown,
click the Home button to send the activity to the background.
5.
Use the DDMS to send an SMS message to the emulator again. This time, note that the activity will
be brought to the foreground, displaying the SMS message received.
How It Works
In the MainActivity class, you first register the BroadcastReceiver in the activity’s onCreate() event,
instead of the onResume() event; and instead of unregistering it in the onPause() event, you now unregister](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-301-320.jpg)
![282 ❘ Chapter 8 Messaging and Networking
Try It Out S
ending E‑mail Programmatically
codefile Emails.zip available for download at Wrox.com
1
. Using Eclipse, create a new Android project and name it Emails.
2 .
Add the following statements in bold to the main.xml file:
<?xml version=”1.0” encoding=”utf-8”?>
<LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android”
android:orientation=”vertical”
android:layout_width=”fill_parent”
android:layout_height=”fill_parent”
>
<Button
android:id=”@+id/btnSendEmail”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:text=”Send Email” />
</LinearLayout>
3
. Add the following statements in bold to the MainActivity.java file:
package net.learn2develop.Email;
import android.app.Activity;
import android.os.Bundle;
import android.content.Intent;
import android.net.Uri;
import android.view.View;
import android.widget.Button;
public class MainActivity extends Activity {
Button btnSendEmail;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
btnSendEmail = (Button) findViewById(R.id.btnSendEmail);
btnSendEmail.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
String[] to = {“weimenglee@learn2develop.net”, “weimenglee@gmail.com”};
String[] cc = {“course@learn2develop.net”};
sendEmail(to, cc, “Hello”, “Hello my friends!”);
}
});](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-304-320.jpg)
![Sending E‑Mail ❘ 283
}
//---sends an SMS message to another device---
private void sendEmail(String[] emailAddresses, String[] carbonCopies,
String subject, String message)
{
Intent emailIntent = new Intent(Intent.ACTION_SEND);
emailIntent.setData(Uri.parse(“mailto:”));
String[] to = emailAddresses;
String[] cc = carbonCopies;
emailIntent.putExtra(Intent.EXTRA_EMAIL, to);
emailIntent.putExtra(Intent.EXTRA_CC, cc);
emailIntent.putExtra(Intent.EXTRA_SUBJECT, subject);
emailIntent.putExtra(Intent.EXTRA_TEXT, message);
emailIntent.setType(“message/rfc822”);
startActivity(Intent.createChooser(emailIntent, “Email”));
}
}
4
. Press F11 to test the application on a real Android device. Click the Send Email button and you
should see the Email application launched in your device, as shown in Figure 8-8.
Figure 8-8
How It Works
In this example, you are launching the built-in Email application to send an e‑mail message. To do so,
you use an Intent object and set the various parameters using the setData(), putExtra(), and setType()
methods:
Intent emailIntent = new Intent(Intent.ACTION_SEND);
emailIntent.setData(Uri.parse(“mailto:”));
String[] to = emailAddresses;
String[] cc = carbonCopies;
emailIntent.putExtra(Intent.EXTRA_EMAIL, to);
emailIntent.putExtra(Intent.EXTRA_CC, cc);
emailIntent.putExtra(Intent.EXTRA_SUBJECT, subject);
emailIntent.putExtra(Intent.EXTRA_TEXT, message);
emailIntent.setType(“message/rfc822”);
startActivity(Intent.createChooser(emailIntent, “Email”));](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-305-320.jpg)
![Networking ❘ 289
Try It Out D
ownloading Plain-Text Files
1
. Using the same project created earlier, add the following statements in bold to the MainActivity
.java file:
public class MainActivity extends Activity {
ImageView img;
private InputStream OpenHttpConnection(String urlString)
throws IOException
{
//...
}
private Bitmap DownloadImage(String URL)
{
//...
}
private String DownloadText(String URL)
{
int BUFFER_SIZE = 2000;
InputStream in = null;
try {
in = OpenHttpConnection(URL);
} catch (IOException e1) {
Toast.makeText(this, e1.getLocalizedMessage(),
Toast.LENGTH_LONG).show();
e1.printStackTrace();
return “”;
}
Do
InputStreamReader isr = new InputStreamReader(in);
int charRead;
String str = “”;
char[] inputBuffer = new char[BUFFER_SIZE];
try {
while ((charRead = isr.read(inputBuffer))>0)
{
//---convert the chars to a String---
String readString =
String.copyValueOf(inputBuffer, 0, charRead);
str += readString;
inputBuffer = new char[BUFFER_SIZE];
}
in.close();
} catch (IOException e) {
Toast.makeText(this, e.getLocalizedMessage(),
Toast.LENGTH_LONG).show();
e.printStackTrace();](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-311-320.jpg)
![Summary ❘ 297
//---download an image---
Bitmap bitmap = DownloadImage(url[0]);
return bitmap;
}
protected void onPostExecute(Bitmap bitmap) {
ImageView img = (ImageView) findViewById(R.id.img);
img.setImageBitmap(bitmap);
}
}
privateInputStreamOpenHttpConnection(StringurlString)
throwsIOException
{
...
}
Basically, you defi ned a class that extends the AsyncTask class. In this case, there are two methods
within the BackgroundTask class — doInBackground() and onPostExecute(). You put all the code
that needs to be run asynchronously in the doInBackground() method. When the task is completed,
the result is passed back via the onPostExecute() method. The onPostExecute() method is executed
on the UI thread, hence it is thread safe to update the ImageView with the bitmap downloaded from
the server.
NOTE You will learn more about the AsyncTask class in Chapter 10 which covers
developing services in Android.
To perform the asynchronous tasks, simply create an instance of the BackgroundTask class and call
its execute() method:
@Override
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new BackgroundTask().execute(
“http://www.streetcar.org/mim/cable/images/cable-01.jpg”);
}
SummAry
This chapter described the various ways to communicate with the outside world. You fi rst learned
how to send and receive SMS messages. You then learned how to send e-mail messages from within
your Android application. Besides SMS and e-mail, another way to communicate with the outside
world is through the use of the HTTP protocol. Using the HTTP protocol, you can download data
from a web server. One good application of this is to talk to Web services, whereby you need to
parse XML fi les.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-319-320.jpg)
![Displaying Maps ❘ 313
Try It Out Navigating the Map to Display a Specific Location
1
. Using the project created in the previous activity, add the following statements in bold to the
MainActivity.java file:
package net.learn2develop.LBS;
import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import com.google.android.maps.MapActivity;
import com.google.android.maps.MapController;
import com.google.android.maps.MapView;
import com.google.android.maps.GeoPoint;
public class MainActivity extends MapActivity {
MapView mapView;
MapController mc;
GeoPoint p;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mapView = (MapView) findViewById(R.id.mapView);
mapView.setBuiltInZoomControls(true);
//mapView.setSatellite(true);
mapView.setStreetView(true);
mc = mapView.getController();
String coordinates[] = {“1.352566007”, “103.78921587”};
double lat = Double.parseDouble(coordinates[0]);
double lng = Double.parseDouble(coordinates[1]);
p = new GeoPoint(
(int) (lat * 1E6),
(int) (lng * 1E6));
mc.animateTo(p);
mc.setZoom(13);
mapView.invalidate();
}
public boolean onKeyDown(int keyCode, KeyEvent event)
{](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-335-320.jpg)
![316 ❘ Chapter 9 Location-Based Services
public boolean draw(Canvas canvas, MapView mapView,
boolean shadow, long when)
{
super.draw(canvas, mapView, shadow);
//---translate the GeoPoint to screen pixels---
Point screenPts = new Point();
mapView.getProjection().toPixels(p, screenPts);
//---add the marker---
Bitmap bmp = BitmapFactory.decodeResource(
getResources(), R.drawable.pushpin);
canvas.drawBitmap(bmp, screenPts.x, screenPts.y-50, null);
return true;
}
}
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mapView = (MapView) findViewById(R.id.mapView);
mapView.setBuiltInZoomControls(true);
//mapView.setSatellite(true);
//mapView.setStreetView(true);
mc = mapView.getController();
String coordinates[] = {“1.352566007”, “103.78921587”};
double lat = Double.parseDouble(coordinates[0]);
double lng = Double.parseDouble(coordinates[1]);
p = new GeoPoint(
(int) (lat * 1E6),
(int) (lng * 1E6));
mc.animateTo(p);
mc.setZoom(13);
//---Add a location marker---
MapOverlay mapOverlay = new MapOverlay();
List<Overlay> listOfOverlays = mapView.getOverlays();
listOfOverlays.clear();
listOfOverlays.add(mapOverlay);
mapView.invalidate();
}
public boolean onKeyDown(int keyCode, KeyEvent event)
{
MapController mc = mapView.getController();
switch (keyCode)](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-338-320.jpg)
![Getting Location Data ❘ 323
import android.content.Context;
//...
//...
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
public class MainActivity extends MapActivity {
MapView mapView;
MapController mc;
GeoPoint p;
private LocationManager lm;
private LocationListener locationListener;
class MapOverlay extends com.google.android.maps.Overlay
{
//...
}
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mapView = (MapView) findViewById(R.id.mapView);
mapView.setBuiltInZoomControls(true);
mc = mapView.getController();
//---navigate to a point first---
String coordinates[] = {“1.352566007”, “103.78921587”};
double lat = Double.parseDouble(coordinates[0]);
double lng = Double.parseDouble(coordinates[1]);
p = new GeoPoint(
(int) (lat * 1E6),
(int) (lng * 1E6));
mc.animateTo(p);
mc.setZoom(13);
//---Add a location marker---
//...
//---reverse geo-coding---
//...
//---use the LocationManager class to obtain locations data---
lm = (LocationManager)
getSystemService(Context.LOCATION_SERVICE);
locationListener = new MyLocationListener();
lm.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
0,](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-345-320.jpg)
![328 ❘ Chapter 9 Location-Based Services
⊲⊲ What You Learned In This Chapter
Topic Key Concepts
Displaying the <com.google.android.maps.MapView
MapView android:id=”@+id/mapView”
android:layout_width=”fill_parent”
android:layout_height=”fill_parent”
android:enabled=”true”
android:clickable=”true”
android:apiKey=”0K2eMNyjc5HFPsiobLh6uLHb8F9ZFmh4uIm7VTA” />
Referencing the <uses-library android:name=”com.google.android.maps” />
Map library
Displaying the mapView.setBuiltInZoomControls(true);
zoom controls
Programmatically mc.zoomIn();
zooming in or out mc.zoomOut();
of the map
Changing views mapView.setSatellite(true);
mapView.setStreetView(true);
mapView.setTraffic(true);
Animating to mc = mapView.getController();
a particular String coordinates[] = {“1.352566007”, “103.78921587”};
double lat = Double.parseDouble(coordinates[0]);
location
double lng = Double.parseDouble(coordinates[1]);
p = new GeoPoint(
(int) (lat * 1E6),
(int) (lng * 1E6));
mc.animateTo(p);
Adding markers Implement an Overlay class and override the draw() method
Getting the loca- GeoPoint p = mapView.getProjection().fromPixels(
tion of the map (int) event.getX(),
(int) event.getY());
touched
Geocoding Use the Geocoder class
and reverse
geocoding](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-350-320.jpg)
![Creating Your Own Services ❘ 339
try {
//---simulate taking some time to download a file---
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//---return an arbitrary number representing
// the size of the file downloaded---
return 100;
}
private class DoBackgroundTask extends AsyncTask<URL, Integer, Long> {
protected Long doInBackground(URL... urls) {
int count = urls.length;
long totalBytesDownloaded = 0;
for (int i = 0; i < count; i++) {
totalBytesDownloaded += DownloadFile(urls[i]);
//---calculate percentage downloaded and
// report its progress---
publishProgress((int) (((i+1) / (float) count) * 100));
}
return totalBytesDownloaded;
}
protected void onProgressUpdate(Integer... progress) {
Log.d(“Downloading files”,
String.valueOf(progress[0]) + “% downloaded”);
Toast.makeText(getBaseContext(),
String.valueOf(progress[0]) + “% downloaded”,
Toast.LENGTH_LONG).show();
}
protected void onPostExecute(Long result) {
Toast.makeText(getBaseContext(),
“Downloaded “ + result + “ bytes”,
Toast.LENGTH_LONG).show();
stopSelf();
}
}
}
2
. Press F11 to debug the application on the Android Emulator.
3
. Click the Start Service button. The Toast class will display a message indicating what percentage of the
download is completed (see Figure 10-4). You should see four of them: 25%, 50%, 75%, and 100%.
4
. You will also observe the following output in the LogCat window:
01-16 02:56:29.051: DEBUG/Downloading files(8844): 25% downloaded
01-16 02:56:34.071: DEBUG/Downloading files(8844): 50% downloaded
01-16 02:56:39.106: DEBUG/Downloading files(8844): 75% downloaded
01-16 02:56:44.173: DEBUG/Downloading files(8844): 100% downloaded](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-361-320.jpg)
![350 ❘ chApter 10 develoPinG android ServiceS
When the intent is received, it invokes an instance of the BroadcastReceiver class that you have defined:
privateBroadcastReceiverintentReceiver=newBroadcastReceiver(){
@Override
publicvoidonReceive(Contextcontext,Intentintent){
Toast.makeText(getBaseContext(),“Filedownloaded!”,
Toast.LENGTH_LONG).show();
}
};
}
NOTE Chapter 8 discusses the BroadcastReceiver class in more detail.
In this case, you displayed the message “File downloaded!” Of course, if you need to pass some data
from the service to the activity, you can make use of the Intent object. The next section discusses this.
Binding ActivitieS to ServiceS
So far, you have seen how services are created and how they are called and terminated when they
are done with their task. All the services that you have seen are simple — either they start with a
counter and increment at regular intervals, or they download a fi xed set of fi les from the Internet.
However, real-world services are usually much more sophisticated, requiring the passing of data
so that they can do the job correctly for you.
Using the service demonstrated earlier that downloads a set of fi les, suppose you now want to let the
Do
calling activity determine what fi les to download, instead of hardcoding them in the service. Here is
what you need to do.
First, in the calling activity, you create an Intent object, specifying the service name:
ButtonbtnStart=(Button)findViewById(R.id.btnStartService);
btnStart.setOnClickListener(newView.OnClickListener(){
publicvoidonClick(Viewv){
Intent intent = new Intent(getBaseContext(), MyService.class);
}
});
You then create an array of URL objects and assign it to the Intent object through its putExtra()
method. Finally, you start the service using the Intent object:
ButtonbtnStart=(Button)findViewById(R.id.btnStartService);
btnStart.setOnClickListener(newView.OnClickListener(){
publicvoidonClick(Viewv){
Intentintent=newIntent(getBaseContext(),MyService.class);
try {
URL[] urls = new URL[] {](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-372-320.jpg)
![Binding Activities to Services ❘ 351
new URL(“http://www.amazon.com/somefiles.pdf”),
new URL(“http://www.wrox.com/somefiles.pdf”),
new URL(“http://www.google.com/somefiles.pdf”),
new URL(“http://www.learn2develop.net/somefiles.pdf”)};
intent.putExtra(“URLs”, urls);
} catch (MalformedURLException e) {
e.printStackTrace();
}
startService(intent);
}
});
Note that the URL array is assigned to the Intent object as an Object array.
On the service’s end, you need to extract the data passed in through the Intent object in the
onStartCommand() method:
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
// We want this service to continue running until it is explicitly
// stopped, so return sticky.
Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show();
Object[] objUrls = (Object[]) intent.getExtras().get(“URLs”);
URL[] urls = new URL[objUrls.length];
for (int i=0; i<objUrls.length-1; i++) {
urls[i] = (URL) objUrls[i];
}
new DoBackgroundTask().execute(urls);
return START_STICKY;
}
The preceding first extracts the data using the getExtras() method to return a Bundle object. It
then uses the get() method to extract out the URL array as an Object array. Because in Java you can-
not directly cast an array from one type to another, you have to create a loop and cast each member
of the array individually. Finally, you execute the background task by passing the URL array into
the execute() method.
This is one way in which your activity can pass values to the service. As you can see, if you have
relatively complex data to pass to the service, you have to do some additional work to ensure that
the data is passed correctly. A better way to pass data is to bind the activity directly to the service so
that the activity can call any public members and methods on the service directly. The following Try
It Out shows you how to bind an activity to a service.
Try It Out Accessing Members of a Property Directly through Binding
1
. Using the same project created earlier, add the following statements in bold to the MyService.java file:
package net.learn2develop.Services;
import java.net.URL;
import java.util.Timer;](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-373-320.jpg)
![352 ❘ Chapter 10 Developing Android Services
import java.util.TimerTask;
import android.app.Service;
import android.content.Intent;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.Toast;
import android.os.IBinder;
import android.os.Binder;
public class MyService extends Service {
int counter = 0;
URL[] urls;
static final int UPDATE_INTERVAL = 1000;
private Timer timer = new Timer();
private final IBinder binder = new MyBinder();
public class MyBinder extends Binder {
MyService getService() {
return MyService.this;
}
}
@Override
public IBinder onBind(Intent arg0) {
//return null;
return binder;
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
// We want this service to continue running until it is explicitly
// stopped, so return sticky.
Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show();
new DoBackgroundTask().execute(urls);
return START_STICKY;
}
@Override
public void onDestroy() {
...
}
private int DownloadFile(URL url) {
...
}
private class DoBackgroundTask extends AsyncTask<URL, Integer, Long> {
...
}
}](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-374-320.jpg)
![Binding Activities to Services ❘ 353
2
. In the MainActivity.java file, add the following statements in bold:
package net.learn2develop.Services;
import java.net.MalformedURLException;
import java.net.URL;
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import android.os.IBinder;
import android.content.ServiceConnection;
public class MainActivity extends Activity {
IntentFilter intentFilter;
private MyService serviceBinder;
Intent i;
private ServiceConnection connection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
//---called when the connection is made---
serviceBinder = ((MyService.MyBinder)service).getService();
try {
URL[] urls = new URL[] {
new URL(“http://www.amazon.com/somefiles.pdf”),
new URL(“http://www.wrox.com/somefiles.pdf”),
new URL(“http://www.google.com/somefiles.pdf”),
new URL(“http://www.learn2develop.net/somefiles.pdf”)};
//---assign the URLs to the service through the serviceBinder object---
serviceBinder.urls = urls;
} catch (MalformedURLException e) {
e.printStackTrace();
}
startService(i);
}
public void onServiceDisconnected(ComponentName className) {
//---called when the service disconnects---
serviceBinder = null;
}
};
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-375-320.jpg)
![Binding Activities to Services ❘ 355
In the onStartCommand() method, you then call the execute() method using the urls array, which you
declared as a public member in your service:
public class MyService extends Service {
int counter = 0;
URL[] urls;
...
...
...
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
// We want this service to continue running until it is explicitly
// stopped, so return sticky.
Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show();
new DoBackgroundTask().execute(urls);
return START_STICKY;
}
This URL array can be set directly from your activity, which you did next.
In the MainActivity.java file, you first declared an instance of your service and an Intent object:
private MyService serviceBinder;
Intent i;
The serviceBinder object will be used as a reference to the service, which you accessed directly.
You then created an instance of the ServiceConnection class so that you could monitor the state of the
service:
private ServiceConnection connection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
//---called when the connection is made---
serviceBinder = ((MyService.MyBinder)service).getService();
try {
URL[] urls = new URL[] {
new URL(“http://www.amazon.com/somefiles.pdf”),
new URL(“http://www.wrox.com/somefiles.pdf”),
new URL(“http://www.google.com/somefiles.pdf”),
new URL(“http://www.learn2develop.net/somefiles.pdf”)};
//---assign the URLs to the service through the serviceBinder object---
serviceBinder.urls = urls;
} catch (MalformedURLException e) {
e.printStackTrace();
}
startService(i);
}
public void onServiceDisconnected(ComponentName className) {
//---called when the service disconnects---
serviceBinder = null;
}
};](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-377-320.jpg)
![356 ❘ Chapter 10 Developing Android Services
You need to implement two methods: onServiceConnected() and onServiceDisconnected().
The onServiceConnected() method is called when the activity is connected to the service; the
onServiceDisconnected()method is called when the service is disconnected from the activity.
In the onServiceConnected() method, when the activity is connected to the service, you obtained an
instance of the service by using the getService() method of the service argument and then assigning
it to the serviceBinder object. The serviceBinder object is a reference to the service, and all the mem-
bers and methods in the service can be accessed through this object. Here, you created an URL array
and then directly assigned it to the public member in the service:
URL[] urls = new URL[] {
new URL(“http://www.amazon.com/somefiles.pdf”),
new URL(“http://www.wrox.com/somefiles.pdf”),
new URL(“http://www.google.com/somefiles.pdf”),
new URL(“http://www.learn2develop.net/somefiles.pdf”)};
//---assign the URLs to the service through the serviceBinder object---
serviceBinder.urls = urls;
You then started the service using an Intent object:
startService(i);
Before you can start the service, you have to bind the activity to the service. This you did in the
onClick() method of the Start Service button:
Button btnStart = (Button) findViewById(R.id.btnStartService);
btnStart.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
i = new Intent(MainActivity.this, MyService.class);
bindService(i, connection, Context.BIND_AUTO_CREATE);
}
});
The bindService() method enables your activity to be connected to the service. It takes three arguments:
an Intent object, a ServiceConnection object, and a flag to indicate how the service should be bound.
Summary
In this chapter, you learned how to create a service in your Android project to execute long-running
tasks. You have seen the many approaches you can use to ensure that the background task is exe-
cuted in an asynchronous fashion, without tying up the main calling activity. You have also learned
how an activity can pass data into a service, and how you can alternatively bind to an activity so
that it can access a service more directly.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-378-320.jpg)
![368 ❘ chApter 11 PUBliShinG android aPPlicationS
(continued)
If you try to install an APK fi le onto a device that already has the APK fi le, it will
display the following error message:
Failure[INSTALL_FAILED_ALREADY_EXISTS]
Figure 11-11 shows an APK fi le successfully installed onto a real device.
Figure 11-11
When you inspect the Launcher on the Android device/emulator, you will be able to see the LBS icon
(on the left of Figure 11-12). If you select Settings➪ Applications➪ Manage Applications on your
Android device/emulator, you will see the “Where Am I” application (on the right in Figure 11-12).
Figure 11-12
Besides using the adb.exe tool to install applications, you can also use it to remove an installed appli-
cation. To do so, you can use the shell option to remove an application from its installed folder:
adb shell rm /data/app/net.learn2develop.LBS.apk
Another way to deploy an application is to use the DDMS tool in Eclipse (see Figure 11-13). With an
emulator (or device) selected, use the File Explorer in DDMS to go to the /data/app folder and use
the “Push a fi le onto the device” button to copy the APK fi le onto the device.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-390-320.jpg)
![Chapter 9 Answers ❘ 413
Chapter 6 Answers
1. The former allows the data to be shared among all the activities in an application, whereas
the latter is accessible only to the activity that created it.
2. The method name is getExternalStorageDirectory().
3. The permission is WRITE_EXTERNAL_STORAGE.
Chapter 7 Answers
1. The code is as follows:
Cursor c = managedQuery(
allContacts,
projection,
ContactsContract.Contacts.DISPLAY_NAME + “ LIKE ?”,
new String[] {“%jack%”} ,
ContactsContract.Contacts.DISPLAY_NAME + “ ASC”);
2. The methods are getType(), onCreate(), query(), insert(), delete(), and update().
3. The code is as follows:
<provider android:name=”BooksProvider”
android:authorities=”net.learn2develop.provider.Books” />
Chapter 8 Answers
1. You can either programmatically send a SMS message from within your Android application
or invoke the built-in Messaging application to send it on your application’s behalf.
2. The two permissions are SEND_SMS and RECEIVE_SMS.
3. The Broadcast receiver should fire a new intent to be received by the activity. The activity
should implement another BroadcastReceiver to listen for this new intent.
4. The permission is INTERNET.
Chapter 9 Answers
1. The likely reasons are as follows:
➤➤ No Internet connection
➤➤ Incorrect placement of the <uses-library> element in the AndroidManifest.xml file
➤➤ Missing INTERNET permission in the AndroidManifest.xml file
2. Geocoding is the act of converting an address into its coordinates (latitude and longitude).
Reverse geocoding converts a pair of location coordinates into an address.](https://image.slidesharecdn.com/beginningandroidapplicationdevelopmentwei-menglee-120617094530-phpapp01/85/Beginning-android-application-development-wei-meng-lee-435-320.jpg)
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- 2. Do
- 3. Beginning Android™ Application Development Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Chapter 1 Getting Started with Android Programming. . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 2 Activities and Intents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Chapter 3 Getting to Know the Android User Interface. . . . . . . . . . . . . . . . . . . . . . . 81 . Chapter 4 Designing Your User Interface Using Views. . . . . . . . . . . . . . . . . . . . . . . 125 Chapter 5 Displaying Pictures and Menus with Views. . . . . . . . . . . . . . . . . . . . . . . 169 . Chapter 6 Data Persistence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Chapter 7 Content Providers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Chapter 8 Messaging and Networking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 Chapter 9 Location-Based Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 Chapter 10 Developing Android Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331 Chapter 11 Publishing Android Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 Appendix A Using Eclipse for Android Development . . . . . . . . . . . . . . . . . . . . . . . . . . 381 Appendix B Using the Android Emulator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393 Appendix C Answers to Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415 .
- 5. Beginning Android™ Application Development Wei-Meng Lee
- 6. Beginning Android™ Application Development Published by Wiley Publishing, Inc. 10475 Crosspoint Boulevard Indianapolis, IN 46256 www.wiley.com Copyright © 2011 by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada ISBN: 978-1-118-01711-1 ISBN: 978-1-118-08729-9 (ebk) ISBN: 978-1-118-08749-7 (ebk) ISBN: 978-1-118-08780-0 (ebk) Manufactured in the United States of America 10 9 8 7 6 5 4 3 2 1 No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permissions. Limit of Liability/Disclaimer of Warranty: The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation warranties of fitness for a particular purpose. No warranty may be created or extended by sales or promotional materials. The advice and strategies contained herein may not be suitable for every situation. This work is sold with the understanding that the publisher is not engaged in rendering legal, accounting, or other professional services. If professional assistance is required, the services of a competent professional person should be sought. Neither the publisher nor the author shall be liable for dam- ages arising herefrom. The fact that an organization or Web site is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Web site may provide or recommendations it may make. Further, readers should be aware that Internet Web sites listed in this work may have changed or disappeared between when this work was written and when it is read. For general information on our other products and services please contact our Customer Care Department within the United States at (877) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Library of Congress Control Number: 2011921777 Trademarks: Wiley, the Wiley logo, Wrox, the Wrox logo, Wrox Programmer to Programmer, and related trade dress are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates, in the United States and other coun- tries, and may not be used without written permission. Android is a trademark of Google, Inc. All other trademarks are the property of their respective owners. Wiley Publishing, Inc., is not associated with any product or vendor mentioned in this book.
- 7. To my family: Thanks for the understanding and support while I worked on getting this book ready! I love you all! —Wei-Meng Lee
- 8. Credits Executive Editor Vice President and Robert Elliott Executive Group Publisher Richard Swadley Senior Project Editor Ami Frank Sullivan Vice President and Executive Publisher Technical Editor Barry Pruett Kunal Mittal Associate Publisher Production Editor Jim Minatel Kathleen Wisor Project Coordinator, Cover Copy Editor Katie Crocker Luann Rouff Compositor Editorial Director James D. Kramer, Robyn B. Siesky Happenstance Type-O-Rama Editorial Manager Proofreader Mary Beth Wakefield Nancy Carrasco Freelancer Editorial Manager Indexer Rosemarie Graham Robert Swanson Associate Director of Marketing Cover Designer David Mayhew Michael E. Trent Production Manager Cover Image Tim Tate © Viktoriya Sukhanova/istockphoto.com
- 9. About the Author Wei-Meng Lee is a technologist and founder of Developer Learning Solutions (www.learn2develop.net), a technology company specializing in hands-on training on the latest mobile technologies. Wei-Meng has many years of training experience, and his training courses place special emphasis on the learning- by-doing approach. This hands-on approach to learning programming makes understanding the subject much easier than reading books, tutorials, and documentation. Wei-Meng is also the author of Beginning iOS 4 Application Development (Wrox), along with sev- eral other Wrox titles. You can contact Wei-Meng at [email protected]. About the Technical Editor Kunal Mittal erves as an Executive Director of Technology at Sony Pictures Entertainment where s he is responsible for the SOA, Identity Management, and Content Management programs. Kunal is an entrepreneur who helps startups define their technology strategy, product roadmap, and develop- ment plans. He generally works in an Advisor or Consulting CTO capacity, and serves actively in the Project Management and Technical Architect functions. He has authored, and edited several books and articles on J2EE, Cloud Computing, and mobile tech- nologies. He holds a Master’s degree in Software Engineering and is an instrument-rated private pilot.
- 10. Acknowledgments Every time I finish a book project, I always tell myself that this will be the last book that I ever write. That’s because writing books is such a time-consuming and laborious effort. However, when you receive e‑mail messages from readers who want to thank you for helping them learn a new tech- nology, all the frustrations disappear. Sure enough, when I finished my previous book on iOS programming, I immediately signed on to do another book — this time about Android. Although you only see the author’s name on the book cover, a lot of people actually worked behind the scenes to make it possible. And now that the book is finally done, it is time to thank a number of those people. First, a huge thanks to Ami Sullivan, my editor, who is always a pleasure to work with. I cannot believe that we have already worked on three books together in such a short duration (only one year) and this is our fourth book! When I hear that Ami is going to be my editor, I know the project is in good hands. Thanks for the guidance, Ami; and thank you for your patience during those times when it seemed like the book was never going to be finished on schedule! I should not forget the heroes behind the scene: copy editor Luann Rouff and technical editor Kunal Mittal. They have been eagle-eye editing the book, making sure that every sentence makes sense — both grammatically as well as technically. Thanks, Luann and Kunal! I also want to take this chance to thank my editor at MobiForge.com, Ruadhan O'Donoghue, who has always been very supportive of my articles. He is always receptive of my ideas and has always been understanding when my schedule falls behind. Thanks for maintaining such a great site, Ruadhan! Last, but not least, I want to thank my parents, and my wife, Sze Wa, for all the support they have given me. They selflessly adjusted their schedules to accommodate mine when I was working on this book. My wife, as always, stayed up late with me on numerous nights as I furiously worked to meet the deadlines, and for this I am very grateful. Finally, to our lovely dog, Ookii, thanks for staying by our side. (For those readers who do not know who Ookii is, you can find two pictures of her in this book. I will leave finding them as an extra exercise for you!)
- 11. Contents Introduction xv Chapter 1: Getting Started with Android Programming 1 What Is Android? 2 Android Versions 2 Features of Android 3 Architecture of Android 3 Android Devices in the Market 4 The Android Market 6 Obtaining the Required Tools 6 Eclipse 7 Android SDK 7 Android Development Tools (ADT) 7 Creating Android Virtual Devices (AVDs) 11 Creating Your First Android Application 14 Anatomy of an Android Application 22 Summary 25 Chapter 2: Activities and Intents 27 Understanding Activities 27 Applying Styles and Themes to Activity 32 Hiding the Activity Title 33 Displaying a Dialog Window 34 Displaying a Progress Dialog 39 Linking Activities Using Intents 43 Resolving Intent Filter Collision 48 Returning Results from an Intent 50 Passing Data Using an Intent Object 54 Calling Built-In Applications Using Intents 56 Understanding the Intent Object 64 Using Intent Filters 65 Adding Categories 71 Displaying Notifications 73 Summary 78
- 12. CONTENTS Chapter 3: Getting to Know the Android User Interface 81 Understanding the Components of a Screen 81 Views and ViewGroups 82 LinearLayout 83 AbsoluteLayout 87 TableLayout 89 RelativeLayout 91 FrameLayout 93 ScrollView 95 Adapting to Display Orientation 97 Anchoring Views 98 Resizing and Repositioning 101 Managing Changes to Screen Orientation 104 Persisting State Information during Changes in Configuration 108 Detecting Orientation Changes 109 Controlling the Orientation of the Activity 110 Creating the User Interface Programmatically 111 Listening for UI Notifications 114 Overriding Methods Defined in an Activity 114 Registering Events for Views 119 Summary 122 Chapter 4: Designing Your User Interface Using Views 125 Basic Views 126 TextView View 126 Button, ImageButton, EditText, CheckBox, ToggleButton, RadioButton, and RadioGroup Views 127 ProgressBar View 135 AutoCompleteTextView View 141 Picker Views 144 TimePicker View 144 Displaying the TimePicker in a Dialog Window 147 DatePicker View 149 Displaying the DatePicker View in a Dialog Window 153 List Views 156 ListView View 156 Customizing the ListView 159 Using the Spinner View 162 Summary 166 x
- 13. CONTENTS Chapter 5: Displaying Pictures and Menus with Views 169 Using Image Views to Display Pictures 169 Gallery and ImageView Views 170 ImageSwitcher 177 GridView 181 Using Menus with Views 185 Creating the Helper Methods 186 Options Menu 188 Context Menu 190 Some Additional Views 193 AnalogClock and DigitalClock Views 194 WebView 194 Summary 200 Chapter 6: Data Persistence 203 Saving and Loading User Preferences 203 Using getSharedPreferences() 204 Using getPreferences() 208 Persisting Data to Files 209 Saving to Internal Storage 209 Saving to External Storage (SD Card) 214 Choosing the Best Storage Option 216 Using Static Resources 217 Creating and Using Databases 218 Creating the DBAdapter Helper Class 218 Using the Database Programmatically 224 Adding Contacts 224 Retrieving All the Contacts 225 Retrieving a Single Contact 226 Updating a Contact 227 Deleting a Contact 228 Upgrading the Database 230 Pre-Creating the Database 230 Bundling the Database with an Application 231 Summary 234 Chapter 7: Content Providers 237 Sharing Data in Android 237 Using a Content Provider 238 Predefined Query String Constants 243 xi
- 14. CONTENTS Projections 246 Filtering 246 Sorting 247 Creating Your Own Content Providers 247 Using the Content Provider 256 Summary 260 Chapter 8: Messaging and Networking 263 SMS Messaging 263 Sending SMS Messages Programmatically 264 Getting Feedback After Sending the Message 267 Sending SMS Messages Using Intent 269 Receiving SMS Messages 270 Updating an Activity from a BroadcastReceiver 273 Invoking an Activity from a BroadcastReceiver 277 Caveats and Warnings 280 Sending E‑Mail 281 Networking 284 Downloading Binary Data 286 Downloading Text Files 288 Accessing Web Services 291 Performing Asynchronous Calls 296 Summary 297 Chapter 9: Location-Based Services 301 Displaying Maps 302 Creating the Project 302 Obtaining the Maps API Key 303 Displaying the Map 305 Displaying the Zoom Control 308 Changing Views 310 Navigating to a Specific Location 312 Adding Markers 315 Getting the Location That Was Touched 318 Geocoding and Reverse Geocoding 320 Getting Location Data 322 Monitoring a Location 327 Summary 327 xii
- 15. CONTENTS Chapter 10: Developing Android Services 331 Creating Your Own Services 331 Performing Long-Running Tasks in a Service 336 Performing Repeated Tasks in a Service 341 Executing Asynchronous Tasks on Separate Threads Using IntentService 343 Communicating between a Service and an Activity 346 Binding Activities to Services 350 Summary 356 Chapter 11: Publishing Android Applications 359 Preparing for Publishing 359 Versioning 360 Digitally Signing Your Android Applications 362 Deploying APK Files 367 Using the adb.exe Tool 367 Using a Web Server 369 Publishing on the Android Market 372 Creating a Developer Profile 372 Submitting Your Apps 373 Summary 378 Appendix A: Using Eclipse for Android Development 3 81 Getting Around in Eclipse 381 Workspaces 381 Package Explorer 382 Using Projects from Other Workspaces 383 Editors 385 Perspectives 387 Auto Import of Namespaces 387 Code Completion 388 Refactoring 388 Debugging 389 Setting Breakpoints 389 Exceptions 390 Appendix B: Using the Android Emulator 393 Uses of the Android Emulator 393 Installing Custom AVDs 393 xiii
- 16. CONTENTS Emulating Real Devices 398 SD Card Emulation 399 Emulating Devices with Different Screen Sizes 401 Emulating Physical Capabilities 402 Sending SMS Messages to the Emulator 403 Making Phone Calls 406 Transferring Files into and out of the Emulator 407 Resetting the Emulator 409 Appendix C: Answers to Exercises 411 Chapter 1 Answers 411 Chapter 2 Answers 411 Chapter 3 Answers 412 Chapter 4 Answers 412 Chapter 5 Answers 412 Chapter 6 Answers 413 Chapter 7 Answers 413 Chapter 8 Answers 413 Chapter 9 Answers 413 Chapter 10 Answers 414 Chapter 11 Answers 414 Index 415 xiv
- 17. introduction i FirSt StArted plAying With the Android Sdk before it was offi cially released as version 1.0. Back then, the tools were unpolished, the APIs in the SDK were unstable, and the documentation was sparse. Fast forward two and a half years, Android is now a formidable mobile operating system, with a fol- lowing no less impressive than the iPhone. Having gone through all the growing pains of Android, I think now is the best time to start learning about Android programming — the APIs have stabilized, and the tools have improved. But one challenge remains: getting started is still an elusive goal for many. It was with this challenge in mind that I was motivated to write this book, one that could benefit begin- ning Android programmers and enable them to write progressively more sophisticated applications. As a book written to help jump-start beginning Android developers, it covers the necessary topics in a linear manner so that you can build on your knowledge without being overwhelmed by the details. I adopt the philosophy that the best way to learn is by doing — hence the numerous Try It Out sec- tions in each chapter, which fi rst show you how to build something and then explain how everything works. Although Android programming is a huge topic, my aim for this book is threefold: to get you started with the fundamentals, to help you understand the underlying architecture of the SDK, and to appre- ciate why things are done in certain ways. It is beyond the scope of any book to cover everything under the sun related to Android programming, but I am confident that after reading this book (and doing the exercises), you will be well equipped to tackle your next Android programming challenge. Who thiS Book iS For This book is targeted for the beginning Android developer who wants to start developing applications using Google’s Android SDK. To truly benefit from this book, you should have some background in programming and at least be familiar with object-oriented programming concepts. If you are totally new to Java — the language used for Android development — you might want to take a programming course in Java programming first, or grab one of many good books on Java programming. In my expe- rience, if you already know C# or VB.NET, learning Java is not too much of an effort; you should be comfortable just following along with the Try It Outs. For those totally new to programming, I know the lure of developing mobile apps and making some money is tempting. However, before attempting to try out the examples in this book, I think a better starting point would be to learn the basics of programming fi rst. NOTE All the examples discussed in this book were written and tested using version 2.3 of the Android SDK. While every effort is made to ensure that all the tools used in this book are the latest, it is always possible that by the time you read this book, a newer version of the tools may be available. If so, some of the instructions and/or screenshots may differ slightly. However, any variations should be manageable.
- 18. introduction What This Book Covers This book covers the fundamentals of Android programming using the Android SDK. It is divided into 11 chapters and three appendices. Chapter 1: Getting Started with Android Programming covers the basics of the Android OS and its current state. You will learn about the features of Android devices, as well as some of the popular devices in the market. You will then learn how to download and install all the required tools to develop Android applications and then test them on the Android Emulator. Chapter 2: Activities and Intents gets you acquainted with the two fundamental concepts in Android programming: activities and intents. Activities are the building blocks of an Android application. You will learn how to link activities together to form a complete Android application using intents, the glue to links activities and one of the unique characteristics of the Android OS. Chapter 3: Getting to Know the Android User Interface covers the various components that make up the UI of an Android application. You will learn about the various layouts you can use to build the UI of your application, and the numerous events that are associated with the UI when users interact with the application. Chapter 4: Designing Your User Interface Using Views walks you through the various basic views you can use to build your Android UI. You will learn three main groups of views: basic views, picker views, and list views. Chapter 5: Displaying Pictures and Menus with Views continues the exploration of views. Here, you will learn how to display images using the various image views, as well as display options and con- text menus in your application. This chapter ends with some additional cool views that you can use to spice up your application. Chapter 6: Data Persistence shows you how to save, or store, data in your Android application. In addition to learning the various techniques to store user data, you will also learn file manipulation and how to save files onto internal and external storage (SD card). In addition, you will learn how to create and use a SQLite database in your Android application. Chapter 7: Content Providers discusses how data can be shared among different applications on an Android device. You will learn how to use a content provider and then build one yourself. Chapter 8: Messaging and Networking explores two of the most interesting topics in mobile pro- gramming — sending SMS messages and network programming. You will learn how to programmat- ically send and receive SMS and e‑mail messages; and how to connect to web servers to download data. Finally, you will see how Web services can be consumed in an Android application. Chapter 9: Location-Based Services demonstrates how to build a location-based service application using Google Maps. You will also learn how to obtain geographical location data and then display the location on the map. Chapter 10: Developing Android Services shows you how you can write applications using services. Services are background applications that run without a UI. You will learn how to run your services asyn- chronously on a separate thread, and how your activities can communicate with them. xvi
- 19. introduction Chapter 11: Publishing Android Applications discusses the various ways you can publish your Android applications when you are ready. You will also learn about the steps to publishing and selling your appli- cations on the Android Market. Appendix A: Using Eclipse for Android Development provides a brief overview of the many features in Eclipse. Appendix B: Using the Android Emulator provides some tips and tricks on using the Android Emulator for testing your applications. Appendix C: Answers to Exercises contains the solutions to the end-of-chapter exercises found in every chapter. How This Book Is Structured This book breaks down the task of learning Android programming into several smaller chunks, enabling you to digest each topic before delving into a more advanced one. If you are a total beginner to Android programming, start with Chapter 1 first. Once you have familiar- ized yourself with the basics, head over to the appendixes to read more about Eclipse and the Android Emulator. When you are ready, continue with Chapter 2 and gradually move into more advanced topics. A feature of this book is that all the code samples in each chapter are independent of those discussed in previous chapters. That way, you have the flexibility to dive into the topics that interest you and start working on the Try It Out projects. What You Need to Use This Book All the examples in this book run on the Android Emulator (which is included as part of the Android SDK). However, to get the most out of this book, having a real Android device would be useful (though not absolutely necessary). Conventions To help you get the most from the text and keep track of what’s happening, a number of conventions are used throughout the book. Try It Out These Are Exercises or Examples for You to Follow The Try It Out sections appear once or more per chapter. These are exercises to work through as you follow the related discussion in the text. . 1 They consist of a set of numbered steps. 2 . Follow the steps with your copy of the project files. xvii
- 20. introduction How It Works After each Try It Out, the code you’ve typed is explained in detail. As for other conventions in the text: ➤➤ New terms and important words are highlighted in italics when first introduced. ➤➤ Keyboard combinations are treated like this: Ctrl+R. ➤➤ Filenames, URLs, and code within the text are treated like so: persistence.properties. ➤➤ Code is presented in two different ways: Weuseamonofonttypewithnohighlightingformostcodeexamples. We use bolding to emphasize code that is of particular importance in the present context. NOTE Notes, tips, hints, tricks, and asides to the current discussion look like this. Source code As you work through the examples in this book, you may choose either to type in all the code manu- ally or to use the source code fi les that accompany the book. All the source code used in this book is available for download at www.wrox.com. When at the site, simply locate the book’s title (use the Search box or one of the title lists) and click the Download Code link on the book’s detail page to obtain all the source code for the book. You’ll fi nd the fi lename of the project you need in a CodeNote such as this at the beginning of the Try it Out features: code snippet filename After you download the code, just decompress it with your favorite compression tool. Alternatively, go to the main Wrox code download page at www.wrox.com/dynamic/books/download.aspx to see the code available for this book and all other Wrox books. NOTE Because many books have similar titles, you may find it easiest to search by ISBN; this book’s ISBN is 978-1-118-01711-1. xviii
- 21. introduction errAtA We make every effort to ensure that there are no errors in the text or in the code. However, no one is perfect, and mistakes do occur. If you fi nd an error in one of our books, such as a spelling mistake or faulty piece of code, we would be very grateful for your feedback. By sending in errata, you may save another reader hours of frustration and at the same time help us provide even higher-quality information. To fi nd the errata page for this book, go to www.wrox.com and locate the title using the Search box or one of the title lists. Then, on the book details page, click the Book Errata link. On this page, you can view all errata that has been submitted for this book and posted by Wrox editors. A complete book list, including links to each book’s errata, is also available at www.wrox.com/misc-pages/booklist.shtml. If you don’t spot “your” error on the Book Errata page, go to www.wrox.com/contact/techsupport .shtml and complete the form there to send us the error you have found. We’ll check the informa- tion and, if appropriate, post a message to the book’s errata page and fi x the problem in subsequent editions of the book. p2p .Wrox .com For author and peer discussion, join the P2P forums at p2p.wrox.com. The forums are a web-based sys- tem for you to post messages relating to Wrox books and related technologies and to interact with other readers and technology users. The forums offer a subscription feature to e-mail you topics of interest of your choosing when new posts are made to the forums. Wrox authors, editors, other industry experts, and your fellow readers are present on these forums. At p2p.wrox.com, you will fi nd a number of different forums that will help you not only as you read Do this book but also as you develop your own applications. To join the forums, just follow these steps: 1 . Go to p2p.wrox.com and click the Register link. 2 . Read the terms of use and click Agree. 3 . Complete the required information to join as well as any optional information you want to provide and click Submit. 4 . You will receive an e-mail with information describing how to verify your account and com- plete the joining process. NOTE You can read messages in the forums without joining P2P, but in order to post your own messages, you must join. xix
- 22. introduction After you join, you can post new messages and respond to messages that other users post. You can read messages at any time on the Web. If you want to have new messages from a particular forum e‑mailed to you, click the Subscribe to This Forum icon by the forum name in the forum listing. For more information about how to use the Wrox P2P, be sure to read the P2P FAQs for answers to questions about how the forum software works, as well as for many common questions specific to P2P and Wrox books. To read the FAQs, click the FAQ link on any P2P page. xx
- 23. 1 getting Started with Android Programming WhAt you Will leArn in thiS chApter ➤➤ What is Android? ➤➤ Android versions and its feature set ➤➤ The Android architecture ➤➤ The various Android devices on the market ➤➤ The Android Market application store ➤➤ How to obtain the tools and SDK for developing Android applications ➤➤ How to develop your first Android application Welcome! The fact that you are holding this book in your hands (or are reading it on your lat- est mobile device) signifies that you are interested in learning how to write applications for the Android platform — and there’s no better time to do this than now! The mobile application market is exploding, and recent market research shows that Android has overtaken iPhone to occupy the second position in the U.S. smartphone market. The fi rst place honor currently goes to Research In Motion (RIM), with Apple’s iPhone taking third place. By the time you read this, chances are good that Android may have become the number one smartphone plat- form in the U.S., and that you may even be reading this on one of the latest Android devices. What propelled this relatively unknown operating system, which Google bought in 2005, to its popular status today? And what features does it offer? In this chapter you will learn what Android is, and what makes it so compelling to both developers and device manufacturers alike. You will also get started with developing your first Android application, and learn how to obtain all the necessary tools and set them up. By the end of this chapter, you will be equipped with the basic knowledge you need to explore more sophisticated techniques and tricks for developing your next killer Android application.
- 24. 2 ❘ Chapter 1 Getting Started with Android Programming What Is Android? Android is a mobile operating system that is based on a modified version of Linux. It was originally developed by a startup of the same name, Android, Inc. In 2005, as part of its strategy to enter the mobile space, Google purchased Android and took over its development work (as well as its develop- ment team). Google wanted Android to be open and free; hence, most of the Android code was released under the open-source Apache License, which means that anyone who wants to use Android can do so by downloading the full Android source code. Moreover, vendors (typically hardware manufacturers) can add their own proprietary extensions to Android and customize Android to differentiate their products from others. This simple development model makes Android very attractive and has thus piqued the interest of many vendors. This has been especially true for companies affected by the phe- nomenon of Apple’s iPhone, a hugely successful product that revolutionized the smartphone industry. Such companies include Motorola and Sony Ericsson, which for many years have been developing their own mobile operating systems. When the iPhone was launched, many of these manufacturers had to scramble to find new ways of revitalizing their products. These manufacturers see Android as a solution — they will continue to design their own hardware and use Android as the operating sys- tem that powers it. The main advantage of adopting Android is that it offers a unified approach to application development. Developers need only develop for Android, and their applications should be able to run on numerous different devices, as long as the devices are powered using Android. In the world of smartphones, appli- cations are the most important part of the success chain. Device manufacturers therefore see Android as their best hope to challenge the onslaught of the iPhone, which already commands a large base of applications. Android Versions Android has gone through quite a number of updates since its first release. Table 1-1 shows the vari- ous versions of Android and their codenames. Table 1-1: A Brief History of Android Versions Android Version Release Date Codename 1.1 9 February 2009 1.5 30 April 2009 Cupcake 1.6 15 September 2009 Donut 2.0/2.1 26 October 2009 Eclair 2.2 20 May 2010 Froyo 2.3 6 December 2010 Gingerbread 3.0 Unconfirmed at the time of writing Honeycomb
- 25. What Is Android? ❘ 3 Features of Android As Android is open source and freely available to manufacturers for customization, there are no fixed hardware and software configurations. However, Android itself supports the following features: ➤➤ Storage — Uses SQLite, a lightweight relational database, for data storage. Chapter 6 discusses data storage in more detail. ➤➤ Connectivity — Supports GSM/EDGE, IDEN, CDMA, EV-DO, UMTS, Bluetooth (includes A2DP and AVRCP), WiFi, LTE, and WiMAX. Chapter 8 discusses networking in more detail. ➤➤ Messaging — Supports both SMS and MMS. Chapter 8 discusses messaging in more detail. ➤➤ Web browser — Based on the open-source WebKit, together with Chrome’s V8 JavaScript engine ➤➤ Media support — Includes support for the following media: H.263, H.264 (in 3GP or MP4 container), MPEG-4 SP, AMR, AMR-WB (in 3GP container), AAC, HE-AAC (in MP4 or 3GP container), MP3, MIDI, Ogg Vorbis, WAV, JPEG, PNG, GIF, and BMP ➤➤ Hardware support — Accelerometer Sensor, Camera, Digital Compass, Proximity Sensor, and GPS ➤➤ Multi-touch — Supports multi-touch screens ➤➤ Multi-tasking — Supports multi-tasking applications ➤➤ Flash support — Android 2.3 supports Flash 10.1. ➤➤ Tethering — Supports sharing of Internet connections as a wired/wireless hotspot Architecture of Android In order to understand how Android works, take a look at Figure 1-1, which shows the various layers that make up the Android operating system (OS). APPLICATIONS Home Contacts Phone Browser ... APPLICATION FRAMEWORK Activity Manager Window Manager Content Providers View System Package Manager Telephony Manager Resource Manager Location Manager Notification Manager LIBRARIES ANDROID RUNTIME Surface Manager Media Framework SQLite Core Libraries OpenGL / ES FreeType WebKit Dalvik Virtual Machine SGL SSL Iibc LINUX KERNEL Display Driver Camera Driver Flash Memory Driver Binder (IPC) Driver Keypad Driver WiFi Driver Audio Drivers Power Management Figure 1-1
- 26. 4 ❘ Chapter 1 Getting Started with Android Programming The Android OS is roughly divided into five sections in four main layers: ➤➤ Linux kernel — This is the kernel on which Android is based. This layer contains all the low- level device drivers for the various hardware components of an Android device. ➤➤ Libraries — These contain all the code that provides the main features of an Android OS. For example, the SQLite library provides database support so that an application can use it for data storage. The WebKit library provides functionalities for web browsing. ➤➤ Android runtime — At the same layer as the libraries, the Android runtime provides a set of core libraries that enable developers to write Android apps using the Java programming language. The Android runtime also includes the Dalvik virtual machine, which enables every Android appli- cation to run in its own process, with its own instance of the Dalvik virtual machine (Android applications are compiled into the Dalvik executables). Dalvik is a specialized virtual machine designed specifically for Android and optimized for battery-powered mobile devices with limited memory and CPU. ➤➤ Application framework — Exposes the various capabilities of the Android OS to application developers so that they can make use of them in their applications. ➤➤ Applications — At this top layer, you will find applications that ship with the Android device (such as Phone, Contacts, Browser, etc.), as well as applications that you download and install from the Android Market. Any applications that you write are located at this layer. Android Devices in the Market Android devices come in all shapes and sizes. As of late November 2010, the Android OS can be seen powering the following types of devices: ➤➤ Smartphones ➤➤ Tablets ➤➤ E-reader devices ➤➤ Netbooks ➤➤ MP4 players ➤➤ Internet TVs Chances are good that you own at least one of the preceding devices. Figure 1-2 shows (clockwise) the Samsung Galaxy S, the HTC Desire HD, and the LG Optimus One smartphones. Another popular category of devices that manufacturers are rushing out is the tablet. Tablet sizes typically start at seven inches, measured diagonally. Figure 1-3 shows the Figure 1-2 Samsung Galaxy Tab and the Dell Streak, which is a five- inch phone tablet.
- 27. What Is Android? ❘ 5 Besides smartphones and tablets, Android is also beginning to appear in dedicated devices, such as e-book readers. Figure 1-4 shows the Barnes and Noble’s NOOKcolor, which is a color e-Book reader running the Android OS. Figure 1-3 Figure 1-4 In addition to these popular mobile devices, Android is also slowly finding its way into your living room. People of Lava, a Swedish company, has developed an Android-based TV, call the Scandinavia Android TV (see Figure 1-5). Google has also ventured into a proprietary smart TV platform based on Android and co-developed with companies such as Intel, Sony, and Logitech. Figure 1-6 shows Sony’s Google TV. Figure 1-5 Figure 1-6
- 28. 6 ❘ chApter 1 GettinG Started with android ProGramminG the Android market As mentioned earlier, one of the main factors determining the success of a smartphone platform is the applications that support it. It is clear from the success of the iPhone that applications play a very vital role in determining whether a new platform swims or sinks. In addition, making these applica- tions accessible to the general user is extremely important. As such, in August 2008, Google announced the Android Market, an online application store for Android devices, and made it available to users in October 2008. Using the Market application that is preinstalled on their Android device, users can simply download third-party applications directly onto their devices. Both paid and free applications are supported on the Android Market, though paid applications are available only to users in certain countries due to legal issues. Similarly, in some countries, users can buy paid applications from the Android Market, but develop- ers cannot sell in that country. As an example, at the time of writing, users in India can buy apps from the Android Market, but developers in India cannot sell apps on the Android Market. The reverse may also be true; for example, users in South Korea cannot buy apps, but developers in South Korea can sell apps on the Android Market. Chapter 11 discusses more about the Android Market and how you can sell your own applications in it. oBtAining the reQuired toolS Now that you know what Android is and its feature set, you are probably anxious to get your hands dirty and start writing some applications! Before you write your fi rst app, however, you need to download the required tools and SDKs. For Android development, you can use a Mac, a Windows PC, or a Linux machine. All the tools needed are free and can be downloaded from the Web. Most of the examples provided in this book should work fi ne with the Android emulator, with the exception of a few examples that require access to the hard- ware. For this book, I will be using a Windows 7 computer to demonstrate all the code samples. If you are using a Mac or Linux computer, the screenshots should look similar; some minor differences may be present, but you should be able to follow along without problems. So, let the fun begin! jAvA jdk The Android SDK makes use of the Java SE Development Kit (JDK). Hence, if your computer does not have the JDK installed, you should start by downloading the JDK from www.oracle.com/technetwork/java/javase/downloads/index.html and install- ing it prior to moving to the next section.
- 29. Obtaining the Required Tools ❘ 7 Eclipse The first step towards developing any applications is obtaining the integrated development environment (IDE). In the case of Android, the recommended IDE is Eclipse, a multi-language software development environment featuring an extensible plug-in system. It can be used to develop various types of applica- tions, using languages such as Java, Ada, C, C++, COBOL, Python, etc. For Android development, you should download the Eclipse IDE for Java EE Developers (www.eclipseorg/downloads/packages/eclipse-ide-java-ee- . developers/heliossr1). Six editions are available: Windows (32 and 64-bit), Mac OS X (Cocoa 32 and 64), and Linux (32 and 64-bit). Simply select the rel- evant one for your operating system. All the examples in this book were tested using the 32-bit version of Eclipse for Windows. Once the Eclipse IDE is downloaded, unzip its content (the eclipse folder) into a folder, say C:Android. Figure 1-7 shows the content of the eclipse folder. Android SDK The next important piece of software you need to download is, of course, the Android SDK. The Android SDK contains a debugger, libraries, an emulator, documentation, sample code, and tutorials. You can download the Android SDK from http://developer.android.com/sdk/ index.html. Figure 1-7 Once the SDK is downloaded, unzip its content (the android-sdk-windows folder) into the C:Android folder, or whatever name you have given to the folder you just created. Android Development Tools (ADT) The Android Development Tools (ADT) plug-in for Eclipse is an extension to the Eclipse IDE that supports the creation and debugging of Android applications. Using the ADT, you will be able to do the following in Eclipse: ➤➤ Create new Android application projects. ➤➤ Access the tools for accessing your Android emulators and devices. ➤➤ Compile and debug Android applications. ➤➤ Export Android applications into Android Packages (APK). ➤➤ Create digital certificates for code-signing your APK. To install the ADT, first launch Eclipse by double-clicking on the eclipse.exe file located in the eclipse folder.
- 30. 8 ❘ Chapter 1 Getting Started with Android Programming When Eclipse is first started, you will be prompted for a folder to use as your workspace. In Eclipse, a workspace is a folder where you store all your projects. Take the default suggested and click OK. Once Eclipse is up and running, select the Help ➪ Install New Software… menu item (see Figure 1-8). In the Install window that appears, type http://dl-ssl.google.com/android/eclipse in the text box (see Figure 1-9) and click Add…. After a while, you will see the Developer Tools item appear in the middle of the window (see Figure 1-10). Expand it, and it will reveal its content: Android DDMS, Android Development Tools, and Android Hierarchy Viewer. Check all of them and click Next. Figure 1-8 Figure 1-9
- 31. Obtaining the Required Tools ❘ 9 Figure 1-10 When you see the installation details, as shown in Figure 1-11, click Next. Figure 1-11
- 32. 10 ❘ chApter 1 GettinG Started with android ProGramminG You will be asked to review the licenses for the tools. Check the option to accept the license agree- ments (see Figure 1-12). Click Finish to continue. Figure 1-12 Eclipse will now proceed to download the tools from the Internet and install them (see Figure 1-13). This will take some time, so be patient. Figure 1-13 NOTE If you have any problems downloading the ADT, check out Google’s help at http://developer.android.com/sdk/eclipse-adt.html#installing. Once the ADT is installed, you will be prompted to restart Eclipse. After doing so, go to Window ➪ Preferences (see Figure 1-14).
- 33. Obtaining the Required Tools ❘ 11 Figure 1-14 In the Preferences window that appears, select Android. You will see an error message saying that the SDK has not been set up (see Figure 1-15). Click OK to dismiss it. Figure 1-15 Enter the location of the Android SDK folder. In this example, it would be C:Android android-sdk-windows. Click OK. Creating Android Virtual Devices (AVDs) The next step is to create AVD to be used for testing your Android applications. AVD stands for Android Virtual Devices. An AVD is an emulator instance that enables you to model an actual device.
- 34. 12 ❘ chApter 1 GettinG Started with android ProGramminG Each AVD consists of a hardware profile, a mapping to a system image, as well as emulated storage, such as a secure digital (SD) card. You can create as many AVDs as you want in order to test your applications with several different configurations. This testing is important to confi rm the behavior of your application when it is run on different devices with varying capabilities. NOTE Appendix B will discuss some of the capabilities of the Android Emulator. To create an AVD, go to Windows ➪ Android SDK and AVD Manager. Select the Available packages option in the left pane and expand the package name shown in the right pane. Figure 1-16 shows the various packages available for you to create AVDs to emulate the differ- ent versions of an Android device. Figure 1-16 Check the relevant tools, documentation, and platforms you need for your project. Once you have selected the items you want, click the Install Selected button to download them. Because it takes a while to download from Google’s server, it is a good idea to download only whatever you need immediately, and download the rest when you have more time.
- 35. Obtaining the Required Tools ❘ 13 NOTE For a start, you should at least select the latest SDK platform. At the time of writing, the latest SDK platform is SDK Platform Android 2.3, API 9, revision 1. Each version of the Android OS is identified by an API level number. For example, Android 2.3 is level 9 (API 9), while Android 2.2 is level 8 (API 8), and so on. For each level, two platforms are available. For example, level 9 offers the following: ➤➤ SDK Platform Android 2.3 ➤➤ Google APIs by Google Inc. The key difference between the two is that the Google APIs platform contains the Google Maps library. Therefore, if the application you are writing requires Google Maps, you need to create an AVD using the Google APIs platform (more on this in Chapter 9, “Location Based Services.” Click the Virtual Devices item in the left pane of the window. Then click the New… button located in the right pane of the window. In the Create new Android Virtual Device (AVD) window, enter the items as shown in Figure 1-17. Click the Create AVD button when you are done. Figure 1-17
- 36. 14 ❘ chApter 1 GettinG Started with android ProGramminG In this case, you have created an AVD (put simply, an Android emulator) that emulates an Android device running version 2.3 of the OS. In addition to what you have created, you also have the option to emulate the device with an SD card and different screen densities and resolutions. NOTE Appendix B explains how to emulate the different types of Android devices. It is preferable to create a few AVDs with different API levels so that your application can be tested on different devices. The example shown in Figure 1-18 shows the many AVDs created to test your applications on a wide variety of different Android platforms. Figure 1-18 creating your First Android Application With all the tools and the SDK downloaded and installed, it is now time to start your engine! As in all programming books, the fi rst example uses the ubiquitous Hello World application. This will enable you to have a detailed look at the various components that make up an Android project. So, without any further ado, let’s dive straight in! try it out Creating Your First Android Application codefile HelloWorld.zip available for download at Wrox.com 1 . Using Eclipse, create a new project by selecting File ➪ Project… (see Figure 1-19).
- 37. Obtaining the Required Tools ❘ 15 Figure 1-19 NOTE After you have created your first Android application, subsequent Android projects can be created by selecting File ➪ New ➪ Android Project. 2 . Expand the Android folder and select Android Project (see Figure 1-20). Figure 1-20
- 38. 16 ❘ chApter 1 GettinG Started with android ProGramminG 3 . Name the Android project as shown in Figure 1-21 and then click Finish. Figure 1-21 NOTE You need to have at least a period (.) in the package name. The rec- ommended convention for the package name is to use your domain name in reverse order, followed by the project name. For example, my company’s domain name is learn2develop.net, hence my package name would be net.learn2develop.HelloWorld. 4 . The Eclipse IDE should now look like Figure 1-22. 5 . In the Package Explorer (located on the left of the Eclipse IDE), expand the HelloWorld project by clicking on the various arrows displayed to the left of each item in the project. In the res/layout folder, double-click the main.xml file (see Figure 1-23).
- 39. Obtaining the Required Tools ❘ 17 Figure 1-22 Figure 1-23 6 . The main.xml file defines the user interface (UI) of your application. The default view is the Layout view, which lays out the activity graphically. To modify the UI, click the main.xml tab located at the bottom (see Figure 1-24).
- 40. 18 ❘ chApter 1 GettinG Started with android ProGramminG Figure 1-24 7 . Add the following code in bold to the main.xml file: <?xmlversion=”1.0”encoding=”utf-8”?> <LinearLayoutxmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent”> <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”@string/hello”/> <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”This is my first Android Application!” /> <Button android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”And this is a clickable button!” /> </LinearLayout> 8 . To save the changes made to your project, press Ctrl+s. 9 . You are now ready to test your application on the Android Emulator. Select the project name in Eclipse and press F11. You will be asked to select a way to debug the application. Select Android Application as shown in Figure 1-25 and click OK. NOTE Some Eclipse installations have an irritating bug: After creating a new proj- ect, Eclipse reports that it contains errors when you try to debug the application. This happens even when you have not modified any files or folders in the project. To solve this problem, simply delete the R.java file located under the gen/net .learn2develop.HelloWorld folder; Eclipse will automatically generate a new R.java file for you. Once this is done, the project shouldn’t contain any errors.
- 41. Obtaining the Required Tools ❘ 19 Figure 1-25 1 0. The Android Emulator will now be started (if the emulator is locked, you need to slide the unlock button to unlock it first). Figure 1-26 shows the application running on the Android Emulator. Figure 1-26 1 1. Click the Home button (the house icon in the lower-left corner above the keyboard) so that it now shows the Home screen (see Figure 1-27).
- 42. 20 ❘ Chapter 1 Getting Started with Android Programming Figure 1-27 1 2. Click the application Launcher icon to display the list of applications installed on the device. Note that the HelloWorld application is now installed in the application launcher (see Figure 1-28). Do Figure 1-28
- 43. Obtaining the Required Tools ❘ 21 Which Avd Will Be uSed to teSt your ApplicAtion? Recall that earlier you created a few AVDs using the AVD Manager. So which one will be launched by Eclipse when you run an Android application? Eclipse will check the target that you specified (when you created a new project), comparing it against the list of AVDs that you have created. The fi rst one that matches will be launched to run your application. If you have more than one suitable AVD running prior to debugging the application, Eclipse will display the Android Device Chooser window, which enables you to select the desired emulator/device to debug the application (see Figure 1-29). Figure 1-29 How It Works To create an Android project using Eclipse, you need to supply the information shown in Table 1-2. tABle 1-2: Project Files Created by Default propertieS deScription Project name The name of the project Application name A user-friendly name for your application Package name The name of the package . You should use a reverse domain name for this . Create Activity The name of the first activity in your application Min SDK Version The minimum version of the SDK that your project is targeting
- 44. 22 ❘ Chapter 1 Getting Started with Android Programming In Android, an Activity is a window that contains the user interface of your applications. An application can have zero or more activities; in this example, the application contains one activity: MainActivity. This MainActivity is the entry point of the application, which is displayed when the application is started. Chapter 2 discusses activities in more detail. In this simple example, you modified the main.xml file to display the string “This is my first Android Application!” and a button. The main.xml file contains the user interface of the activity, which is dis- played when MainActivity is loaded. When you debug the application on the Android Emulator, the application is automatically installed on the emulator. And that’s it — you have developed your first Android application! The next section unravels how all the various files in your Android project work together to make your application come alive. Anatomy of an Android Application Now that you have created your first Hello World Android application, it is time to dissect the innards of the Android project and examine all the parts that make everything work. First, note the various files that make up an Android project in the Package Explorer in Eclipse (see Figure 1-30). The various folders and their files are as follows: ➤➤ src — Contains the .java source files for your project. In this example, there is one file, MainActivity.java. The MainActivity.java file is the source file for your activity. You will write the code for your application in this file. ➤➤ Android 2.3 library — This item contains one file, android.jar, which contains all the class libraries needed for an Android application. ➤➤ gen — Contains the R.java file, a compiler-generated file that references all the resources found in your project. You should not modify this file. ➤➤ assets — This folder contains all the assets used by your Figure 1-30 application, such as HTML, text files, databases, etc. ➤➤ res — This folder contains all the resources used in your application. It also contains a few other subfolders: drawable-<resolution>, layout, and values. Chapter 3 talks more about how you can support devices with different screen resolutions and densities. ➤➤ AndroidManifest.xml — This is the manifest file for your Android application. Here you spec- ify the permissions needed by your application, as well as other features (such as intent-filters, receivers, etc.). Chapter 2 discusses the use of the AndroidManifest.xml file in more details.
- 45. Obtaining the Required Tools ❘ 23 The main.xml file defines the user interface for your activity. Observe the following in bold: <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”@string/hello” /> The @string in this case refers to the strings.xml file located in the res/values folder. Hence, @string/hello refers to the hello string defined in the strings.xml file, which is “Hello World, MainActivity!”: <?xml version=”1.0” encoding=”utf-8”?> <resources> <string name=”hello”>Hello World, MainActivity!</string> <string name=”app_name”>HelloWorld</string> </resources> It is recommended that you store all the string constants in your application in this strings.xml file and reference these strings using the @string identifier. That way, if you ever need to localize your application to another language, all you need to do is replace the strings stored in the strings.xml file with the targeted language and recompile your application. Observe the content of the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.HelloWorld” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”9” /> </manifest> The AndroidManifest.xml file contains detailed information about the application: ➤➤ It defines the package name of the application as net.learn2develop.HelloWorld. ➤➤ The version code of the application is 1. This value is used to identify the version number of your application. It can be used to programmatically determine whether an application needs to be upgraded. ➤➤ The version name of the application is 1.0. This string value is mainly used for display to the user. You should use the format: <major>.<minor>.<point> for this value. ➤➤ The application uses the image named icon.png located in the drawable folder.
- 46. 24 ❘ chApter 1 GettinG Started with android ProGramminG ➤➤ The name of this application is the string named app_name defined in the strings.xml file. ➤➤ There is one activity in the application represented by the MainActivity.java file. The label displayed for this activity is the same as the application name. ➤➤ Within the definition for this activity, there is an element named <intent-filter>: ➤➤ The action for the intent filter is named android.intent.action.MAIN to indicate that this activity serves as the entry point for the application. ➤➤ The category for the intent-filter is named android.intent.category.LAUNCHER to indicate that the application can be launched from the device’s Launcher icon. Chapter 2 discusses intents in more details. ➤➤ Finally, the android:minSdkVersion attribute of the <uses-sdk> element specifies the minimum version of the OS on which the application will run. As you add more fi les and folders to your project, Eclipse will automatically generate the content of R.java, which at the moment contains the following: packagenet.learn2develop.HelloWorld; publicfinalclassR{ publicstaticfinalclassattr{ } publicstaticfinalclassdrawable{ publicstaticfinalinticon=0x7f020000; } publicstaticfinalclasslayout{ publicstaticfinalintmain=0x7f030000; } publicstaticfinalclassstring{ publicstaticfinalintapp_name=0x7f040001; publicstaticfinalinthello=0x7f040000; } } You are not supposed to modify the content of the R.javafi le; Eclipse automatically generates the content for you when you modify your project. NOTE If you delete R.java manually, Eclipse will regenerate it for you imme- diately. Note that in order for Eclipse to generate the R.java file for you, the project must not contain any errors. If you realize that Eclipse has not regener- ated R.java after you have deleted it, check your project again. The code may contain syntax errors, or your XML files (such as AndroidManifest.xml, main.xml, etc.) may not be well-formed.
- 47. Summary ❘ 25 Finally, the code that connects the activity to the UI (main.xml) is the setContentView() method, which is in the MainActivity.java file: package net.learn2develop.HelloWorld; import android.app.Activity; import android.os.Bundle; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } } Here, R.layout.main refers to the main.xml file located in the res/layout folder. As you add additional XML files to the res/layout folder, the filenames will automatically be generated in the R.java file. The onCreate() method is one of many methods that are fired when an activity is loaded. Chapter 2 discusses the life cycle of an activity in more detail. Summary This chapter has provided a brief overview of Android, and highlighted some of its capabilities. If you have followed the sections on downloading the tools and SDK, you should now have a work- ing system — one that is capable of developing more interesting Android applications other than the Hello World application. In the next chapter, you will learn about the concepts of activities and intents, and the very important roles they play in Android. Exercises 1 . What is an AVD? 2 . What is the difference between the android:versionCode and android:versionName attributes in the AndroidManifest.xml file? 3. What is the use of the strings.xml file? Answers to the Exercises can be found in Appendix C.
- 48. 26 ❘ Chapter 1 Getting Started with Android Programming ⊲⊲ What You Learned In This Chapter Topic Key Concepts Android OS Android is an open-source mobile operating system based on the Linux operating system. It is available to anyone who wants to adapt it to run on their own devices. Languages used for You use the Java programming language to develop Android appli- Android application cations. Written applications are compiled into Dalvik executables, development which are then run on top of the Dalvik Virtual Machine. Android Market The Android Market hosts all the various Android applications written by third-party developers. Tools for Android Eclipse IDE, Android SDK, and the ADT Application Development Activity An activity is represented by a screen in your Android application. Each application can have zero or more activities. The Android manifest file The AndroidManifest.xml file contains detailed configuration infor- mation for your application. As your application gets more sophisti- cated, you will modify this file, and you will see the different information you can add to this file as you progress through the chapters.
- 49. 2 Activities and intents WhAt you Will leArn in thiS chApter ➤➤ What activities are ➤➤ How to apply styles and themes to activities ➤➤ How to display activities as dialog windows ➤➤ Understanding the concept of intents ➤➤ How to use the Intent object to link activities ➤➤ How intent filters help you to selectively connect to other activities ➤➤ How to display alerts to the user using notifications In Chapter 1, you learned that an activity is a window that contains the user interface of your applications. An application can have zero or more activities. Typically, applications have one or more activities, and the main aim of an activity is to interact with the user. From the moment an activity appears on the screen to the moment it is hidden, it goes through a number of stages, known as an activity’s life cycle. Understanding the life cycle of an activity is vital to ensuring that your application works correctly. In this chapter, you will learn more about how activities work and the things that you need to take note of when designing your Android application. Apart from activities, another unique concept in Android is that of an intent. An intent is basically the “glue” that enables different activities from different applications to work together seamlessly, ensuring that tasks can be performed as though they all belong to one single application. In the second part of this chapter, you will learn more about this very important concept and how you can use it to call built-in applications such as the Browser, Phone, Maps, and more. underStAnding ActivitieS This chapter begins by looking at how to create an activity. To create an activity, you create a Java class that extends the Activity base class: packagenet.learn2develop.Activities;
- 50. 28 ❘ Chapter 2 Activities and Intents import android.app.Activity; import android.os.Bundle; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } } Your activity class would then load its UI component using the XML file defined in your res/layout folder. In this example, you would load the UI from the main.xml file: setContentView(R.layout.main); Every activity you have in your application must be declared in your AndroidManifest.xml file, like this: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Activities” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”9” /> </manifest> The Activity base class defines a series of events that governs the life cycle of an activity. The Activity class defines the following events: ➤➤ onCreate() — Called when the activity is first created ➤➤ onStart() — Called when the activity becomes visible to the user ➤➤ onResume() — Called when the activity starts interacting with the user ➤➤ onPause() — Called when the current activity is being paused and the previous activity is being resumed ➤➤ onStop() — Called when the activity is no longer visible to the user ➤➤ onDestroy() — Called before the activity is destroyed by the system (either manually or by the system to conserve memory) ➤➤ onRestart() — Called when the activity has been stopped and is restarting again
- 51. Understanding Activities ❘ 29 By default, the activity created for you contains the onCreate() event. Within this event handler is the code that helps to display the UI elements of your screen. Figure 2-1 shows the life cycle of an activity and the various stages it goes through — from when the activity is started until it ends. Activity starts onCreate() User navigates back to the activity onStart() onRestart() onResume() Process is killed Activity is running The activity comes to the foreground Another activity comes in front of the activity Other applications onPause() need memory The activity comes to the The activity is no longer visible foreground onStop() onDestroy() Activity is shut down Image reproduced from work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License. See http://developer.android.com/reference/android/app/Activity.html Figure 2-1
- 52. 30 ❘ Chapter 2 Activities and Intents The best way to understand the various stages experienced by an activity is to create a new project, implement the various events, and then subject the activity to various user interactions. Try It Out Understanding the Life Cycle of an Activity codefile Activities.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it as shown in Figure 2-2. Figure 2-2 2 . In the MainActivity.java file, add the following statements in bold: package net.learn2develop.Activities; import android.app.Activity; import android.os.Bundle; import android.util.Log; public class MainActivity extends Activity { String tag = “Events”; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Log.d(tag, “In the onCreate() event”);
- 53. Understanding Activities ❘ 31 } public void onStart() { super.onStart(); Log.d(tag, “In the onStart() event”); } public void onRestart() { super.onRestart(); Log.d(tag, “In the onRestart() event”); } public void onResume() { super.onResume(); Log.d(tag, “In the onResume() event”); } public void onPause() { super.onPause(); Log.d(tag, “In the onPause() event”); } public void onStop() { super.onStop(); Log.d(tag, “In the onStop() event”); } public void onDestroy() { super.onDestroy(); Log.d(tag, “In the onDestroy() event”); } } 3 . Press F11 to debug the application on the Android Emulator. 4. When the activity is first loaded, you should see the following in the LogCat window (click on the Debug perspective; see also Figure 2-3): 12-28 13:45:28.115: DEBUG/Events(334): In the onCreate() event 12-28 13:45:28.115: DEBUG/Events(334): In the onStart() event 12-28 13:45:28.115: DEBUG/Events(334): In the onResume() event Figure 2-3
- 54. 32 ❘ chApter 2 activitieS and intentS 5 . When you now press the back button on the Android Emulator, observe that the following is printed: 12-2813:59:46.266:DEBUG/Events(334):IntheonPause()event 12-2813:59:46.806:DEBUG/Events(334):IntheonStop()event 12-2813:59:46.806:DEBUG/Events(334):IntheonDestroy()event 6 . Click the Home button and hold it there. Click the Activities icon and observe the following: 12-2814:00:54.115:DEBUG/Events(334):IntheonCreate()event 12-2814:00:54.156:DEBUG/Events(334):IntheonStart()event 12-2814:00:54.156:DEBUG/Events(334):IntheonResume()event 7 . Press the Phone button on the Android Emulator so that the activity is pushed to the background. Observe the output in the LogCat window: 12-2814:01:16.515:DEBUG/Events(334):IntheonPause()event 12-2814:01:17.135:DEBUG/Events(334):IntheonStop()event 8 . Notice that the onDestroy() event is not called, indicating that the activity is still in memory. Exit the phone dialer by pressing the Back button. The activity is now visible again. Observe the output in the LogCat window: 12-2814:02:17.255:DEBUG/Events(334):IntheonRestart()event 12-2814:02:17.255:DEBUG/Events(334):IntheonStart()event 12-2814:02:17.255:DEBUG/Events(334):IntheonResume()event The onRestart() event is now fi red, followed by the onStart() and onResume() events. How It Works As you can see from this simple experiment, an activity is destroyed when you press the Back button. This is crucial to know, as whatever state the activity is currently in will be lost; hence, you need to write additional code in your activity to preserve its state when it is destroyed (Chapter 3 will show you how). At this point, note that the onPause() event is called in both scenarios — when an activity is sent to the background, as well as when it is killed when the user presses the Back button. When an activity is started, the onStart() and onResume() events are always called, regardless of whether the activity is restored from the background or newly created. NOTE Even if an application has only one activity and the activity is killed, the application will still be running in memory. Applying Styles and themes to Activity By default, an activity occupies the entire screen. However, you can also apply a dialog theme to an activity so that it is displayed as a floating dialog. For example, you might want to customize your activ- ity to display as a pop-up, warning the user about some actions that they are going to perform. In this case, displaying the activity as a dialog is a good way to get their attention.
- 55. Understanding Activities ❘ 33 To apply a dialog theme to an activity, simply modify the <Activity> element in the AndroidManifest.xml file by adding the android:theme attribute: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Activities” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name” android:theme=”@android:style/Theme.Dialog” > <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”9” /> </manifest> Doing so will make the activity appear as a dialog, as shown in Figure 2-4. Hiding the Activity Title You can also hide the title of an activity if desired (such as when you just want to display a status update to the user). To do so, use the requestWindowFeature() method and pass it the Window.FEATURE_NO_ TITLE constant, like this: package net.learn2develop.Activities; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.view.Window; public class MainActivity extends Activity { String tag = “Events”; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //---hides the title bar--- requestWindowFeature(Window.FEATURE_NO_TITLE); setContentView(R.layout.main); Log.d(tag, “In the onCreate() event”); } } This will hide the title bar, as shown in Figure 2-5.
- 56. 34 ❘ Chapter 2 Activities and Intents Figure 2-4 Figure 2-5 Displaying a Dialog Window There are times where you need to display a dialog window to get a confirmation from the user. In this case, you can override the onCreateDialog() protected method defined in the base Activity class to display a dialog window. The following Try It Out shows you how. Try It Out Displaying a Dialog Window Using an Activity codefile Dialog.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it Dialog. . 2 Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”@string/hello” /> <Button android:id=”@+id/btn_dialog” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Click to display a dialog” /> </LinearLayout>
- 57. Understanding Activities ❘ 35 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Dialog; import android.app.Activity; import android.os.Bundle; import android.app.AlertDialog; import android.app.Dialog; import android.content.DialogInterface; import android.view.View; import android.widget.Button; import android.widget.Toast; public class MainActivity extends Activity { CharSequence[] items = { “Google”, “Apple”, “Microsoft” }; boolean[] itemsChecked = new boolean [items.length]; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button btn = (Button) findViewById(R.id.btn_dialog); btn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { showDialog(0); } }); } @Override protected Dialog onCreateDialog(int id) { switch (id) { case 0: return new AlertDialog.Builder(this) .setIcon(R.drawable.icon) .setTitle(“This is a dialog with some simple text...”) .setPositiveButton(“OK”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(getBaseContext(), “OK clicked!”, Toast.LENGTH_SHORT).show(); } }) .setNegativeButton(“Cancel”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(getBaseContext(), “Cancel clicked!”, Toast.LENGTH_SHORT).show(); } })
- 58. 36 ❘ Chapter 2 Activities and Intents .setMultiChoiceItems(items, itemsChecked, new DialogInterface.OnMultiChoiceClickListener() { @Override public void onClick(DialogInterface dialog, int which, boolean isChecked) { Toast.makeText(getBaseContext(), items[which] + (isChecked ? “ checked!”: “ unchecked!”), Toast.LENGTH_SHORT).show(); } } ) .create(); } return null; } } 4 . Press F11 to debug the application on the Android Emulator. Click the button to display the dialog (see Figure 2-6). Checking the various checkboxes will cause the Toast class to display the text of the item checked/unchecked. To dismiss the dialog, click the OK or Cancel button. Figure 2-6 How It Works To display a dialog, you first override the onCreateDialog() method in the Activity class: @Override protected Dialog onCreateDialog(int id) { //... }
- 59. Understanding Activities ❘ 37 This method is called when you call the showDialog() method: Button btn = (Button) findViewById(R.id.btn_dialog); btn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { showDialog(0); } }); The onCreateDialog() method is a callback for creating dialogs that are managed by the activity. When you call the showDialog() method, this callback will be invoked. The showDialog() method accepts an integer argument identifying a particular dialog to display. To create a dialog, you use the AlertDialog class’s Builder constructor. You set the various properties, such as icon, title, and buttons, as well as checkboxes: @Override protected Dialog onCreateDialog(int id) { switch (id) { case 0: return new AlertDialog.Builder(this) .setIcon(R.drawable.icon) .setTitle(“This is a dialog with some simple text...”) .setPositiveButton(“OK”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(getBaseContext(), “OK clicked!”, Toast.LENGTH_SHORT).show(); } }) .setNegativeButton(“Cancel”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(getBaseContext(), “Cancel clicked!”, Toast.LENGTH_SHORT).show(); } }) .setMultiChoiceItems(items, itemsChecked, new DialogInterface.OnMultiChoiceClickListener() { @Override public void onClick(DialogInterface dialog, int which, boolean isChecked) { Toast.makeText(getBaseContext(), items[which] + (isChecked ? “ checked!”: “ unchecked!”), Toast.LENGTH_SHORT).show(); } } ) .create(); } return null; }
- 60. 38 ❘ chApter 2 activitieS and intentS The preceding code sets two buttons: OK and Cancel, using the setPositiveButton() and setNegativeButton() methods, respectively. You also set a list of checkboxes for users to choose via the setMultiChoiceItems() method. For the setMultiChoiceItems() method, you passed in two arrays: one for the list of items to display and another to contain the value of each item to indicate if they are checked. When each item is checked, you use the Toast class to display a message (see Figure 2-7). Figure 2-7 the context oBject In Android, you will often encounter the Context class and its instances. Instances of the Context class are often used to provide reference to your application. For exam- ple, in this example, the fi rst parameter of the Toast class takes in a Context object. returnnewAlertDialog.Builder(this) .setIcon(R.drawable.icon) .setTitle(“Thisisadialogwithsomesimpletext...”) .setPositiveButton(“OK”,new DialogInterface.OnClickListener(){ publicvoidonClick(DialogInterfacedialog, intwhichButton) { Toast.makeText(getBaseContext(), “OKclicked!”,Toast.LENGTH_SHORT).show(); Do } }) ... But because the Toast() class is not used directly in the activity (it is used within the AlertDialog class), you need to return an instance of the Context class by using the getBaseContext() method. Another area where you will encounter the Context class is when creating a view dynamically in an activity. For example, you may want to dynamically create a TextView view from code. To do so, you instantiate the TextView class, like this: TextViewtv=newTextView(this); The constructor for the TextView class takes a Context object, and because the Activity class is a subclass of Context, you can use the this keyword to represent the Context object.
- 61. Understanding Activities ❘ 39 Displaying a Progress Dialog Besides the plain dialog that you created in the previous section, you can also create a progress dialog. A progress dialog is useful for showing the progress of some activities, such as the status of a download operation. The following Try It Out shows you how to display a progress dialog. Try It Out Displaying a Progress Dialog Window Using an Activity 1 . Using the same project created in the previous section, add the following statements in bold to the MainActivity.java file: package net.learn2develop.Dialog; import android.app.Activity; import android.app.AlertDialog; import android.app.Dialog; import android.content.DialogInterface; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.Toast; import android.app.ProgressDialog; import android.os.Handler; import android.os.Message; public class MainActivity extends Activity { CharSequence[] items = { “Google”, “Apple”, “Microsoft” }; boolean[] itemsChecked = new boolean [items.length]; private ProgressDialog _progressDialog; private int _progress = 0; private Handler _progressHandler; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button btn = (Button) findViewById(R.id.btn_dialog); btn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { showDialog(1); _progress = 0; _progressDialog.setProgress(0); _progressHandler.sendEmptyMessage(0); } }); _progressHandler = new Handler() {
- 62. 40 ❘ Chapter 2 Activities and Intents public void handleMessage(Message msg) { super.handleMessage(msg); if (_progress >= 100) { _progressDialog.dismiss(); } else { _progress++; _progressDialog.incrementProgressBy(1); _progressHandler.sendEmptyMessageDelayed(0, 100); } } }; } @Override protected Dialog onCreateDialog(int id) { switch (id) { case 0: return new AlertDialog.Builder(this) //... //... .create(); case 1: _progressDialog = new ProgressDialog(this); _progressDialog.setIcon(R.drawable.icon); _progressDialog.setTitle(“Downloading files...”); _progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); _progressDialog.setButton(DialogInterface.BUTTON_POSITIVE, “Hide”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(getBaseContext(), “Hide clicked!”, Toast.LENGTH_SHORT).show(); } }); _progressDialog.setButton(DialogInterface.BUTTON_NEGATIVE, “Cancel”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(getBaseContext(), “Cancel clicked!”, Toast.LENGTH_SHORT).show(); } }); return _progressDialog; } return null; } } 2 . Press F11 to debug the application on the Android Emulator. Click the button to display the prog- ress dialog (see Figure 2-8). Observe that the progress bar will count up to 100.
- 63. Understanding Activities ❘ 41 Figure 2-8 How It Works To create a progress dialog, you first create an instance of the ProgressDialog class and set its various properties, such as icon, title, and style: _progressDialog = new ProgressDialog(this); _progressDialog.setIcon(R.drawable.icon); _progressDialog.setTitle(“Downloading files...”); _progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); You then set the two buttons that you want to display inside the progress dialog: _progressDialog.setButton(DialogInterface.BUTTON_POSITIVE, “Hide”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(getBaseContext(), “Hide clicked!”, Toast.LENGTH_SHORT).show(); } }); _progressDialog.setButton(DialogInterface.BUTTON_NEGATIVE, “Cancel”, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { Toast.makeText(getBaseContext(), “Cancel clicked!”, Toast.LENGTH_SHORT).show();
- 64. 42 ❘ Chapter 2 Activities and Intents } }); return _progressDialog; } The preceding causes a progress dialog to appear (see Figure 2-9). Figure 2-9 To display the progress status in the progress dialog, you need to use a Handler object to run a back- ground thread: _progress = 0; _progressDialog.setProgress(0); _progressHandler.sendEmptyMessage(0); The background thread counts up to 100, with each count delayed by 100 milliseconds: _progressHandler = new Handler() { public void handleMessage(Message msg) { super.handleMessage(msg); if (_progress >= 100) { _progressDialog.dismiss(); } else { _progress++; _progressDialog.incrementProgressBy(1); _progressHandler.sendEmptyMessageDelayed(0, 100); } } }; When the count reaches 100, the progress dialog is dismissed.
- 65. Linking Activities Using intents ❘ 43 linking ActivitieS uSing intentS An Android application can contain zero or more activities. When your application has more than one activity, you may need to navigate from one activity to another. In Android, you navigate between activi- ties through what is known as an intent. The best way to understand this very important but somewhat abstract concept in Android is to experi- ence it firsthand and see what it helps you to achieve. The following Try It Out shows how to add another activity to an existing project and then navigate between the two activities. try it out Linking Activities with intents 1 . Using the Activities project created earlier, add the following statements in bold to the AndroidManifest.xml file: <?xmlversion=”1.0”encoding=”utf-8”?> <manifestxmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Activities” android:versionCode=”1” android:versionName=”1.0”> <applicationandroid:icon=”@drawable/icon”android:label=”@string/app_name”> <activityandroid:name=”.MainActivity” android:label=”@string/app_name” android:theme=”@android:style/Theme.Dialog” > <intent-filter> <actionandroid:name=”android.intent.action.MAIN”/> <categoryandroid:name=”android.intent.category.LAUNCHER”/> </intent-filter> </activity> <activity android:name=”.Activity2” android:label=”Activity 2”> <intent-filter> <action android:name=”net.learn2develop.ACTIVITY2” /> <category android:name=”android.intent.category.DEFAULT” /> </intent-filter> </activity> </application> <uses-sdkandroid:minSdkVersion=”9”/> NOTE You’ll need to remove the attribute that has strikethrough applied. 2 . Right click on the package name under the src folder and select New ➪ Class (see Figure 2-10). 3 . Name the new class file Activity2 (see Figure 2-11) and click Finish.
- 66. 44 ❘ Chapter 2 Activities and Intents 4 . Make a copy of the main.xml file by right-clicking on it and selecting Copy. Then, right-click on the res/layout folder and select Paste. Name the file activity2.xml. The res/layout folder will now contain the activity2.xml file (see Figure 2-12). Figure 2-10 Figure 2-11 Figure 2-12 5 . Modify the activity2.xml file as follows: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” >
- 67. Linking Activities Using Intents ❘ 45 <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”This is Activity 2!” /> </LinearLayout> 6 . In the Activity2.java file, add the following statements in bold: package net.learn2develop.Activities; import android.app.Activity; import android.os.Bundle; public class Activity2 extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity2); } } 7 . Modify the MainActivity.java file as shown in bold: package net.learn2develop.Activities; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.view.Window; import android.view.KeyEvent; import android.content.Intent; public class MainActivity extends Activity { String tag = “Events”; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //---hides the title bar--- //requestWindowFeature(Window.FEATURE_NO_TITLE); setContentView(R.layout.main); Log.d(tag, “In the onCreate() event”); } public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) { startActivity(new Intent(“net.learn2develop.ACTIVITY2”));
- 68. 46 ❘ Chapter 2 Activities and Intents } return false; } public void onStart() { //... } public void onRestart() { //... } public void onResume() { //... } public void onPause() { //... } public void onStop() { //... } public void onDestroy() { //... } } 8 . Press F11 to debug the application on the Android Emulator. When the first activity is loaded, click the center of the directional pad (see Figure 2-13; on a real device this can be achieved by pressing down the trackball). The second activity will now be loaded. Figure 2-13 How It Works As you have learned, an activity is made up of a UI component (for example, main.xml) and a class component (for example, MainActivity.java). Hence, if you want to add another activity to a project, you need to create these two components. In the AndroidManifest.xml file, specifically you have added the following: <activity android:name=”.Activity2” android:label=”Activity 2”>
- 69. Linking Activities Using Intents ❘ 47 <intent-filter> <action android:name=”net.learn2develop.ACTIVITY2” /> <category android:name=”android.intent.category.DEFAULT” /> </intent-filter> </activity> Here, you have added a new activity to the application. Note the following: ➤➤ The name of the new activity added is “Activity2”. ➤➤ The label for the activity is named “Activity 2”. ➤➤ The intent filter name for the activity is “net.learn2develop.ACTIVITY2”. Other activities that wish to call this activity will invoke it via this name. Ideally, you should use the reverse domain name of your company as the intent filter name in order to reduce the chances of another application having the same intent filter. The next section discusses what happens when two or more activities have the same intent filter. ➤➤ The category for the intent filter is “android.intent.category.DEFAULT”. You need to add this to the intent filter so that this activity can be started by another activity using the startActivity() method (more on this shortly). In the MainActivity.java file, you implemented the onKeyDown event handler. This event is fired when- ever the user presses one of the keys on the device. When the user presses the center key on the direc- tional pad (as represented by the KeyEvent.KEYCODE_DPAD_CENTER constant), you use the startActivity() method to display Activity2 by creating an instance of the Intent class and passing it the intent filter name of Activity2 (which is net.learn2develop.ACTIVITY2): public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) { startActivity(new Intent(“net.learn2develop.ACTIVITY2”)); } return false; } Activities in Android can be invoked by any application running on the device. For example, you can create a new Android project and then display Activity2 by using its net.learn2develop.ACTIVITY2 intent filter. This is one of the fundamental concepts in Android that enables an application to invoke another easily. If the activity that you want to invoke is defined within the same project, you can rewrite the preceding statement like this: startActivity(new Intent(this, Activity2.class)); However, this approach is applicable only when the activity you want to display is within the same project as the current activity.
- 70. 48 ❘ Chapter 2 Activities and Intents Resolving Intent Filter Collision In the previous section, you learned that the <intent-filter> element defines how your activity can be invoked by another activity. What happens if another activity (in either the same or a separate application) has the same filter name? For example, suppose your application has another activity named Activity3, with the following entry in the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Activities” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name” > <! -- android:theme=”@android:style/Theme.Dialog” -- > <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> <activity android:name=”.Activity2” android:label=”Activity 2”> <intent-filter> <action android:name=”net.learn2develop.ACTIVITY2” /> <category android:name=”android.intent.category.DEFAULT” /> </intent-filter> </activity> <activity android:name=”.Activity3” android:label=”Activity 3”> <intent-filter> <action android:name=”net.learn2develop.ACTIVITY2” /> <category android:name=”android.intent.category.DEFAULT” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”9” /> </manifest> If you call the startActivity() method with the following intent, then the Android OS will display a selection as shown in Figure 2-14: startActivity(new Intent(“net.learn2develop.ACTIVITY2”)); If you check the “Use by default for this action” item and then select an activity, then the next time the intent “net.learn2develop.ACTIVITY2” is called again, it will always launch the previous activ- ity that you have selected. To clear away this default, go to the Settings application in Android and select Applications ➪ Manage applications and select the application name (see Figure 2-15). When the details of the application are shown, scroll down to the bottom and click the Clear defaults button.
- 71. Linking Activities Using Intents ❘ 49 Figure 2-14 Figure 2-15
- 72. 50 ❘ Chapter 2 Activities and Intents Returning Results from an Intent The startActivity() method invokes another activity but does not return a result to the current activity. For example, you may have an activity that prompts the user for username and password. The information entered by the user in that activity needs to be passed back to the calling activity for further processing. If you need to pass data back from an activity, you should instead use the startActivityForResult() method. The following Try It Out demonstrates this. Try It Out Obtaining a Result from an Activity 1 . Using the same project created in the previous section, add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Please enter your name” /> <EditText android:id=”@+id/txt_username” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <Button android:id=”@+id/btn_OK” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”OK” /> </LinearLayout> 2 . Add the following statements in bold to Activity2.java: package net.learn2develop.Activities; import android.app.Activity; import android.os.Bundle; import android.content.Intent; import android.net.Uri; import android.view.View; import android.widget.Button; import android.widget.EditText; public class Activity2 extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity2); //---get the OK button--- Button btn = (Button) findViewById(R.id.btn_OK); //---event handler for the OK button---
- 73. Linking Activities Using Intents ❘ 51 btn.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { Intent data = new Intent(); //---get the EditText view--- EditText txt_username = (EditText) findViewById(R.id.txt_username); //---set the data to pass back--- data.setData(Uri.parse( txt_username.getText().toString())); setResult(RESULT_OK, data); //---closes the activity--- finish(); } }); } } 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Activities; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.view.Window; import android.view.KeyEvent; import android.widget.Toast; import android.content.Intent; public class MainActivity extends Activity { String tag = “Events”; int request_Code = 1; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //---hides the title bar--- //requestWindowFeature(Window.FEATURE_NO_TITLE); setContentView(R.layout.main); Log.d(tag, “In the onCreate() event”); } public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) { //startActivity(new Intent(“net.learn2develop.ACTIVITY2”)); //startActivity(new Intent(this, Activity2.class)); startActivityForResult(new Intent(
- 74. 52 ❘ Chapter 2 Activities and Intents “net.learn2develop.ACTIVITY2”), request_Code); } return false; } public void onActivityResult(int requestCode, int resultCode, Intent data) { if (requestCode == request_Code) { if (resultCode == RESULT_OK) { Toast.makeText(this,data.getData().toString(), Toast.LENGTH_SHORT).show(); } } } public void onStart() { //... } public void onRestart() { //... } public void onResume() { //... } public void onPause() { //... } public void onStop() { //... } public void onDestroy() { //... } } 4 . Press F11 to debug the application on the Android Emulator. When the first activity is loaded, click the center button on the directional pad. Activity2 will now be loaded. Enter your name (see Figure 2-16) and click the OK button. You will see that the first activity now displays the name you have entered using the Toast class. Figure 2-16
- 75. Linking Activities Using intents ❘ 53 How It Works To call an activity and wait for a result to be returned from it, you need to use the startActivityForResult() method, like this: startActivityForResult(new Intent( “net.learn2develop.ACTIVITY2”), request_Code); In addition to passing in an Intent object, you need to pass in request code as well. The request code is simply an integer value that identifies an activity you are calling. This is needed because when an activity returns a value, you must have a way to identify it. For example, you may be calling multiple activities at the same time and some activities may not return immediately (for example, waiting for a reply from a server). When an activity returns, you need this request code to determine which activity is actually returned. NOTE If the request code is set to -1, then calling it using the startActivityForResult() method is equivalent to calling it using the startActivity() method. That is, no result will be returned. In order for an activity to return a value to the calling activity, you use an Intent object to send data back via the setData() method: Intentdata=newIntent(); //---gettheEditTextview--- EditTexttxt_username= (EditText)findViewById(R.id.txt_username); //---setthedatatopassback--- data.setData(Uri.parse( txt_username.getText().toString())); setResult(RESULT_OK,data); //---closestheactivity--- finish(); The setResult() method sets a result code (either RESULT_OK or RESULT_CANCELLED) and the data (an Intent object) to be returned back to the calling activity. The finish() method closes the activity and returns control back to the calling activity. In the calling activity, you need to implement the onActivityResult() method, which is called whenever an activity returns: publicvoidonActivityResult(intrequestCode,intresultCode,Intentdata) { if(requestCode==request_Code){ if(resultCode==RESULT_OK){ Toast.makeText(this,data.getData().toString(),
- 76. 54 ❘ Chapter 2 Activities and Intents Toast.LENGTH_SHORT).show(); } } } Here, you check for the appropriate request code and display the result that is returned. The returned result is passed in via the data argument; and you obtain its details through the getData() method. Passing Data Using an Intent Object Besides returning data from an activity, it is also common to pass data to an activity. For example, in the previous example you may want to set some default text in the EditText view before the activ- ity is displayed. In this case, you can use the Intent object to pass the data to the target activity. The following Try It Out shows you how. Try It Out Passing Data to the Target Activity 1 . Using the same project created in the previous section, add the following statements in bold to the MainActivity.java file: public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) { //startActivity(new Intent(“net.learn2develop.ACTIVITY2”)); //startActivity(new Intent(this, Activity2.class)); /* startActivityForResult(new Intent( “net.learn2develop.ACTIVITY2”), request_Code); */ Intent i = new Intent(“net.learn2develop.ACTIVITY2”); Bundle extras = new Bundle(); extras.putString(“Name”, “Your name here”); i.putExtras(extras); startActivityForResult(i, 1); } return false; } 2 . Add the following statements in bold to Activity2.java: public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity2); String defaultName=””; Bundle extras = getIntent().getExtras(); if (extras!=null) {
- 77. Linking Activities Using intents ❘ 55 defaultName = extras.getString(“Name”); } //---get the EditText view--- EditText txt_username = (EditText) findViewById(R.id.txt_username); txt_username.setHint(defaultName); //---gettheOKbutton--- Buttonbtn=(Button)findViewById(R.id.btn_OK); //---eventhandlerfortheOKbutton--- btn.setOnClickListener(newView.OnClickListener() { //... }); } 3 . Press F11 to debug the application on the Android Emulator. When you click the center button of the directional keypad, notice that the EditText view in the target activity displays the hint text (see Figure 2-17). Do Figure 2-17 NOTE The hint text is placeholder text that is commonly found in EditText views. It is displayed when the view is empty, and it disappears as soon as the user types something into it. It is useful for displaying hints that tell users what type of information they should enter.
- 78. 56 ❘ Chapter 2 Activities and Intents How It Works To use the Intent object to carry data to the target activity, you made use of a Bundle object: Bundle extras = new Bundle(); extras.putString(“Name”, “Your name here”); i.putExtras(extras); A Bundle object is basically a dictionary object that enables you to set data in key/value pairs. In this case, you created a key named Name and assigned it a value of “Your name here”. The Bundle object is then added to the Intent object using the putExtras() method. In the target activity, you first use the getIntent() method to obtain the intent that started the activity. You then use the getExtras() method to obtain the Bundle object: Bundle extras = getIntent().getExtras(); if (extras!=null) { defaultName = extras.getString(“Name”); } The getString() method retrieves the Name key from the Bundle object. The string retrieved is then assigned to the EditText view using the setHint() method: //---get the EditText view--- EditText txt_username = (EditText) findViewById(R.id.txt_username); txt_username.setHint(defaultName); Calling Built-In Applications Using Intents Until this point, you have seen how to call activities within your own application. One of the key aspects of Android programming is using the intent to call activities from other applications. In par- ticular, your application can call the many built-in applications that are included with an Android device. For example, if your application needs to enable a user to call a particular person saved in the Contacts application, you can simply use an Intent object to bring up the Contacts application, from which the user can select the person to call. This enables your application to present a consis- tent user experience, and enables you to avoid building another application to retrieve all the con- tacts in the Contacts application. The following Try It Out demonstrates how to call some of the built-in applications commonly found on an Android device. Try It Out Calling Built-In Applications Using Intents codefile Intents.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it Intents.
- 79. Calling Built-In Applications Using Intents ❘ 57 2 . Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <Button android:id=”@+id/btn_webbrowser” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Web Browser” /> <Button android:id=”@+id/btn_makecalls” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Make Calls” /> <Button android:id=”@+id/btn_showMap” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Show Map” /> <Button android:id=”@+id/btn_chooseContact” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Choose Contact” /> </LinearLayout> 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Intents; import android.app.Activity; import android.os.Bundle; import android.content.Intent; import android.net.Uri; import android.provider.ContactsContract; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.Toast; public class MainActivity extends Activity { Button b1, b2, b3, b4; int request_Code = 1; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---Web browser button---
- 80. 58 ❘ Chapter 2 Activities and Intents b1 = (Button) findViewById(R.id.btn_webbrowser); b1.setOnClickListener(new OnClickListener() { public void onClick(View arg0){ Intent i = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“http://www.amazon.com”)); startActivity(i); } }); //---Make calls button--- b2 = (Button) findViewById(R.id.btn_makecalls); b2.setOnClickListener(new OnClickListener() { public void onClick(View arg0){ Intent i = new Intent(android.content.Intent.ACTION_DIAL, Uri.parse(“tel:+651234567”)); startActivity(i); } }); //---Show Map button--- b3 = (Button) findViewById(R.id.btn_showMap); b3.setOnClickListener(new OnClickListener() { public void onClick(View arg0){ Intent i = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“geo:37.827500,-122.481670”)); startActivity(i); } }); //---Choose Contact button--- b4 = (Button) findViewById(R.id.btn_chooseContact); b4.setOnClickListener(new OnClickListener() { public void onClick(View arg0){ Intent i = new Intent(android.content.Intent.ACTION_PICK); i.setType(ContactsContract.Contacts.CONTENT_TYPE); startActivityForResult(i,request_Code); } }); } public void onActivityResult(int requestCode, int resultCode, Intent data) { if (requestCode == request_Code) { if (resultCode == RESULT_OK) {
- 81. Calling Built-in Applications Using intents ❘ 59 Toast.makeText(this,data.getData().toString(), Toast.LENGTH_SHORT).show(); Intent i = new Intent( android.content.Intent.ACTION_VIEW, Uri.parse(data.getData().toString())); startActivity(i); } } } } 4 . Press F11 to debug the application on the Android Emulator. 5 . Click the Web Browser button to load the Browser application on the emulator (see Figure 2-18). Figure 2-18 6 . Click the Make Calls button and the Phone application will load (see Figure 2-19). 7 . Similarly, to load the Maps application, shown in Figure 2-20, click the Show Map button. NOTE In order to display the Maps application, you need to run the application on an AVD that supports the Google APIs. 8 . Click the Choose Contact application to show a list of contacts that you can select (see Figure 2-21). Selecting a contact will show details about that contact.
- 82. 60 ❘ Chapter 2 Activities and Intents Figure 2-19 Figure 2-20 Figure 2-21 How It Works In this example, you saw how you can use the Intent class to invoke some of the built-in applications in Android (such as Maps, Phone, Contacts, and Browser).
- 83. Calling Built-in Applications Using intents ❘ 61 In Android, intents usually come in pairs: action and data. The action describes what is to be performed, such as editing an item, viewing the content of an item, and so on. The data specifies what is affected, such as a person in the Contacts database. The data is specified as an Uri object. Some examples of action are as follows: ➤➤ ACTION_VIEW ➤➤ ACTION_DIAL ➤➤ ACTION_PICK Some examples of data include the following: ➤➤ http://www.google.com ➤➤ tel:+651234567 ➤➤ geo:37.827500,-122.481670 ➤➤ content://contacts NOTE The section “Using Intent Filters” will explain the type of data you can define for use in an activity. Collectively, the action and data pair describes the operation to be performed. For example, to dial a phone number, you would use the pair ACTION_DIAL/tel:+651234567. To display a list of contacts stored in your phone, you use the pair ACTION_VIEW/content://contacts. To pick a contact from the list of contacts, you use the pair ACTION_PICK/content://contacts. In the fi rst button, you create an Intent object and then pass two arguments to its constructor — the action and the data: Intenti=new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“http://www.amazon.com”)); startActivity(i); The action here is represented by the android.content.Intent.ACTION_VIEW constant. You use the parse() method of the Uri class to convert an URL string into an Uri object. The android.content.Intent.ACTION_VIEW constant actually refers to the “android.intent.action .VIEW” action, so the preceding could be rewritten as follows: Intenti=new Intent(“android.intent.action.VIEW”, Uri.parse(“http://www.amazon.com”)); startActivity(i); The preceding code snippet can also be rewritten like this: Intenti=new Intent(“android.intent.action.VIEW”);
- 84. 62 ❘ chApter 2 activitieS and intentS i.setData(Uri.parse(“http://www.amazon.com”)); startActivity(i); Here, you set the data separately using the setData() method. For the second button, you dial a specific number by passing in the telephone number in the data portion: Intent i = new Intent(android.content.Intent.ACTION_DIAL, Uri.parse(“tel:+651234567”)); startActivity(i); In this case, the dialer will display the number to be called. The user must still press the dial button to dial the number. If you want to directly call the number without user intervention, change the action as follows: Intenti=new Intent(android.content.Intent.ACTION_CALL, Uri.parse(“tel:+651234567”)); startActivity(i); NOTE If you want your application to directly call the specified number, you need to add the android.permission.CALL_PHONE permission to your application. If you simply want to display the dialer without specifying any number, simply omit the data portion, like this: Intenti=new Intent(android.content.Intent.ACTION_DIAL); startActivity(i); The third button displays a map using the ACTION_VIEW constant: Intenti=new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“geo:37.827500,-122.481670”)); startActivity(i); Here, instead of using “http” you use the “geo” scheme. The fourth button invokes the Contacts application to enable the user to pick a contact. Because you are asking the user to select a contact, you need the Contacts application to return a value; in this case, you need to set the type of data to indicate what kind of data needs to be returned: Intenti=new Intent(android.content.Intent.ACTION_PICK); i.setType(ContactsContract.Contacts.CONTENT_TYPE); startActivityForResult(i,request_Code); If you want to view and select only those contacts with a phone number, you could set the type as follows: i.setType( ContactsContract.CommonDataKinds.Phone.CONTENT_TYPE);
- 85. Calling Built-In Applications Using Intents ❘ 63 In this case, the contacts and their phone numbers are displayed (see Figure 2-22). Figure 2-22 Because you are expecting a result from the Contacts application, you invoke it using the startActivityForResult() method, passing in the Intent object and a request code. You need to implement the onActivityResult() method in order to obtain a result from the activity: public void onActivityResult(int requestCode, int resultCode, Intent data) { if (requestCode == request_Code) { if (resultCode == RESULT_OK) { Toast.makeText(this,data.getData().toString(), Toast.LENGTH_SHORT).show(); Intent i = new Intent( android.content.Intent.ACTION_VIEW, Uri.parse(data.getData().toString())); startActivity(i); } } } In the case of the Contacts application, when you choose a particular contact (using the ACTION_PICK constant), an URL containing the contact selected is returned, like this: content://com.android.contacts/contacts/loopup/0r1-1234567890/1
- 86. 64 ❘ Chapter 2 Activities and Intents Obtaining this URL is not very useful unless you know what to do with it. Therefore, in this case, you can create another Intent object to view it: Intent i = new Intent( android.content.Intent.ACTION_VIEW, Uri.parse(data.getData().toString())); startActivity(i); This will show details about the selected contact. Understanding the Intent Object So far, you have seen the use of the Intent object to call other activities. This is a good time to recap and gain a more detailed understanding of how the Intent object performs its magic. First, you see that you can call another activity by passing its action to the constructor of an Intent object: startActivity(new Intent(“net.learn2develop.ACTIVITY2”)); The action (in this example “net.learn2develop.ACTIVITY2”) is also known as the component name. This is used to identify the target activity/application that you want to invoke. You can also rewrite the component name by specifying the class name of the activity if it resides in your project, like this: startActivity(new Intent(this, Activity2.class)); You can also create an Intent object by passing in an action constant and data, such as the following: Intent i = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“http://www.amazon.com”)); startActivity(i); The action portion defines what you want to do, while the data portion contains the data for the tar- get activity to act upon. You can also pass the data to the Intent object using the setData() method: Intent i = new Intent(android.content.Intent.ACTION_VIEW); i.setData(Uri.parse(“http://www.amazon.com”)); In this example, you indicate that you want to view a web page with the specified URL. The Android OS will look for all activities that are able to satisfy your request. This process is known as intent resolution. The next section discusses in more detail how your activities can be the target of other activities. For some intents, there is no need to specify the data. For example, to select a contact from the Contacts application, you specify the action and then indicate the MIME type using the setType() method: Intent i = new Intent(android.content.Intent.ACTION_PICK); i.setType(ContactsContract.Contacts.CONTENT_TYPE);
- 87. Calling Built-In Applications Using Intents ❘ 65 The setType() method explicitly specifies the MIME data type to indicate the type of data to return. The MIME type for ContactsContract.Contacts.CONTENT_TYPE is “vnd.android.cursor .dir/contact”. Besides specifying the action, the data, and the type, an Intent object can also specify a category. A category groups activities into logical units so that Android can use it for further filtering. The next section discusses categories in more details. To summarize, an Intent object can contain the following information: ➤➤ Action ➤➤ Data ➤➤ Type ➤➤ Category Using Intent Filters Earlier, you saw how an activity can invoke another activity using the Intent object. In order for other activities to invoke your activity, you need to specify the action and category within the <intent-filter> element in the AndroidManifest.xml file, like this: <intent-filter> <action android:name=”net.learn2develop.ACTIVITY2” /> <category android:name=”android.intent.category.DEFAULT” /> </intent-filter> This is a very simple example in which one activity calls another using the “net.learn2develop .ACTIVITY2” action. The following Try It Out shows you a more sophisticated example. Try It Out Specifying Intent Filters in More Details 1 . Using the Intents project created earlier, add a new class to the project and name it MyBrowserActivity .java. Also add a new XML file to the res/layout folder and name it browser.xml (see Figure 2-23). Figure 2-23
- 88. 66 ❘ Chapter 2 Activities and Intents 2 . Add the following statements in bold to the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Intents” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> <activity android:name=”.MyBrowserActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.VIEW” /> <action android:name=”net.learn2develop.MyBrowser” /> <category android:name=”android.intent.category.DEFAULT” /> <data android:scheme=”http” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”9” /> <uses-permission android:name=”android.permission.CALL_PHONE” /> <uses-permission android:name=”android.permission.INTERNET” /> </manifest> 3 . Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <Button android:id=”@+id/btn_webbrowser” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Web Browser” /> <Button android:id=”@+id/btn_makecalls” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Make Calls” /> <Button android:id=”@+id/btn_showMap” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Show Map” /> <Button android:id=”@+id/btn_chooseContact”
- 89. Calling Built-In Applications Using Intents ❘ 67 android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Choose Contact” /> <Button android:id=”@+id/btn_launchMyBrowser” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Launch My Browser” /> </LinearLayout> 4 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Intents; import android.app.Activity; import android.content.Intent; import android.net.Uri; import android.os.Bundle; import android.provider.ContactsContract; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.Toast; public class MainActivity extends Activity { Button b1, b2, b3, b4, b5; int request_Code = 1; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---Web browser button--- b1 = (Button) findViewById(R.id.btn_webbrowser); b1.setOnClickListener(new OnClickListener() { //... }); //---Make calls button--- b2 = (Button) findViewById(R.id.btn_makecalls); b2.setOnClickListener(new OnClickListener() { //... }); //---Show Map button--- b3 = (Button) findViewById(R.id.btn_showMap); b3.setOnClickListener(new OnClickListener() { //...
- 90. 68 ❘ Chapter 2 Activities and Intents }); //---Choose Contact button--- b4 = (Button) findViewById(R.id.btn_chooseContact); b4.setOnClickListener(new OnClickListener() { //... }); b5 = (Button) findViewById(R.id.btn_launchMyBrowser); b5.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { Intent i = new Intent(“net.learn2develop.MyBrowser”); i.setData(Uri.parse(“http://www.amazon.com”)); startActivity(i); } }); } public void onActivityResult(int requestCode, int resultCode, Intent data) { //... } } 5 . Add the following statements in bold to the browser.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <WebView android:id=”@+id/WebView01” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> </LinearLayout> 6 . Add the following statements in bold to the MyBrowserActivity.java file: package net.learn2develop.Intents; import android.app.Activity; import android.net.Uri; import android.os.Bundle; import android.webkit.WebView; import android.webkit.WebViewClient; public class MyBrowserActivity extends Activity {
- 91. Calling Built-In Applications Using Intents ❘ 69 /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.browser); Uri url = getIntent().getData(); WebView webView = (WebView) findViewById(R.id.WebView01); webView.setWebViewClient(new Callback()); webView.loadUrl(url.toString()); } private class Callback extends WebViewClient { @Override public boolean shouldOverrideUrlLoading(WebView view, String url) { return(false); } } } 7 . Press F11 to debug the application on the Android Emulator. 8 . Click the Launch my Browser button and you should see the new activity displaying the Amazon.com web page (see Figure 2-24). Figure 2-24
- 92. 70 ❘ Chapter 2 Activities and Intents How It Works In this example, you created a new activity named MyBrowserActivity. You first needed to declare it in the AndroidManifest.xml file: <activity android:name=”.MyBrowserActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.VIEW” /> <action android:name=”net.learn2develop.MyBrowser” /> <category android:name=”android.intent.category.DEFAULT” /> <data android:scheme=”http” /> </intent-filter> </activity> In the <intent-filter> element, you declared it to have two actions, one category, and one data. This means that all other activities can invoke this activity using either the “android.intent.action.VIEW” or the “net.learn2develop.MyBrowser” action. For all activities that you want others to call using the start Activity() or startActivityForResult() methods, they need to have the “android.intent.category .DEFAULT” category. If not, your activity will not be callable by others. The <data> element specifies the type of data expected by the activity. In this case, it expects the data to start with the “http://” prefix. The preceding intent filter could also be rewritten as follows: <activity android:name=”.MyBrowserActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.VIEW” /> <category android:name=”android.intent.category.DEFAULT” /> <data android:scheme=”http” /> </intent-filter> <intent-filter> <action android:name=”net.learn2develop.MyBrowser” /> <category android:name=”android.intent.category.DEFAULT” /> <data android:scheme=”http” /> </intent-filter> </activity> Writing the intent filter this way makes it much more readable and logically groups the action, category, and data within an intent filter. If you now use the ACTION_VIEW action with the data shown here, Android will display a selection (as shown in Figure 2-25): Intent i = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“http://www.amazon.com”)); startActivity(i); You can choose between using the Browser application or the Intents application that you are currently building.
- 93. Calling Built-In Applications Using Intents ❘ 71 Figure 2-25 Adding Categories You can group your activities into categories by using the <category> element in the intent filter. Suppose you have added the following <category> element to the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Intents” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> <activity android:name=”.MyBrowserActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.VIEW” /> <action android:name=”net.learn2develop.MyBrowser” /> <category android:name=”android.intent.category.DEFAULT” /> <category android:name=”net.learn2develop.Apps” />
- 94. 72 ❘ Chapter 2 Activities and Intents <data android:scheme=”http” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”9” /> <uses-permission android:name=”android.permission.CALL_PHONE” /> <uses-permission android:name=”android.permission.INTERNET” /> </manifest> In this case, the following code will invoke the MyBrowerActivity activity: Intent i = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“http://www.amazon.com”)); i.addCategory(“net.learn2develop.Apps”); startActivity(i); You add the category to the Intent object using the addCategory() method. If you omit the addCategory() statement, the preceding code will still invoke the MyBrowerActivity activity because it will still match the default category “android.intent.category.DEFAULT”. However, if you specify a category that does not match the category defined in the intent filter, it will not work: Intent i = new Intent(“net.learn2develop.MyBrowser”, Uri.parse(“http://www.amazon.com”)); //---this category does not match any in the intent-filter--- i.addCategory(“net.learn2develop.OtherApps”); startActivity(i); The preceding category (“net.learn2develop.OtherApps”) does not match any in the intent filter, so a run-time exception will be raised. If you add the preceding category in the intent filter of MyBrowerActivity, then the preceding code will work: <intent-filter> <action android:name=”android.intent.action.VIEW” /> <action android:name=”net.learn2develop.MyBrowser” /> <category android:name=”android.intent.category.DEFAULT” /> <category android:name=”net.learn2develop.Apps” /> <category android:name=”net.learn2develop.OtherApps” /> <data android:scheme=”http” /> </intent-filter> You can add multiple categories to an Intent object; for example, the following statements add the “net.learn2develop.SomeOtherApps” category to the Intent object: Intent i = new Intent(“net.learn2develop.MyBrowser”, Uri.parse(“http://www.amazon.com”)); i.addCategory(“net.learn2develop.OtherApps”); i.addCategory(“net.learn2develop.SomeOtherApps”); startActivity(i);
- 95. Displaying Notifications ❘ 73 Because the intent filter does not define the “net.learn2develop.SomeOtherApps” category, the pre- ceding code will not be able to invoke the MyBrowerActivity activity. To fix this, you need to add the “net.learn2develop.SomeOtherApps” category to the intent filter again. From this example, it is evident that when using an Intent object with categories, all categories added to the Intent object must fully match those defined in the intent filter before an activity can be invoked. Displaying Notifications So far, you have been using the Toast class to display messages to the user. While the Toast class is a handy way to show users alerts, it is not persistent. It flashes on the screen for a few seconds and then disappears. If it contains important information, users may easily miss it if they are not looking at the screen. For messages that are important, you should use a more persistent method. In this case, you should use the NotificationManager to display a persistent message at the top of the device, commonly known as the status bar (sometimes also referred to as the notification bar). The following Try It Out demonstrates how. Try It Out Displaying Notifications on the Status Bar codefile Notifications.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it Notifications. 2 . Add a new class file named NotificationView.java to the src folder of the project (see Figure 2-26). In addition, add a new notification.xml file to the res/layout folder as well. Figure 2-26 3 . Populate the notification.xml file as follows: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent”
- 96. 74 ❘ Chapter 2 Activities and Intents android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Here are the details for the notification...” /> </LinearLayout> 4 . Populate the NotificationView.java file as follows: package net.learn2develop.Notifications; import android.app.Activity; import android.app.NotificationManager; import android.os.Bundle; public class NotificationView extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.notification); //---look up the notification manager service--- NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE); //---cancel the notification that we started nm.cancel(getIntent().getExtras().getInt(“notificationID”)); } } 5 . Add the following statements in bold to the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Notifications” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> <activity android:name=”.NotificationView” android:label=”Details of notification”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.DEFAULT” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”9” />
- 97. Displaying Notifications ❘ 75 <uses-permission android:name=”android.permission.VIBRATE” /> </manifest> 6 . Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <Button android:id=”@+id/btn_displaynotif” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Display Notification” /> </LinearLayout> 7 . Finally, add the following statements in bold to the MainActivity.java file: package net.learn2develop.Notifications; import android.app.Activity; import android.os.Bundle; import android.app.Notification; import android.app.NotificationManager; import android.app.PendingIntent; import android.content.Intent; import android.view.View; import android.widget.Button; public class MainActivity extends Activity { int notificationID = 1; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button button = (Button) findViewById(R.id.btn_displaynotif); button.setOnClickListener(new Button.OnClickListener() { public void onClick(View v) { displayNotification(); } }); } protected void displayNotification() { //---PendingIntent to launch activity if the user selects // this notification--- Intent i = new Intent(this, NotificationView.class); i.putExtra(“notificationID”, notificationID); PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, i, 0);
- 98. 76 ❘ Chapter 2 Activities and Intents NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE); Notification notif = new Notification( R.drawable.icon, “Reminder: Meeting starts in 5 minutes”, System.currentTimeMillis()); CharSequence from = “System Alarm”; CharSequence message = “Meeting with customer at 3pm...”; notif.setLatestEventInfo(this, from, message, pendingIntent); //---100ms delay, vibrate for 250ms, pause for 100 ms and // then vibrate for 500ms--- notif.vibrate = new long[] { 100, 250, 100, 500}; nm.notify(notificationID, notif); } } 8 . Press F11 to debug the application on the Android Emulator. 9. Click the Display Notification button (see the top left of Figure 2-27) and a notification will appear on the status bar. 10. Clicking and dragging the status bar down will reveal the notification (see the right of Figure 2-27). 11. Clicking on the notification will reveal the NotificationView activity. This also causes the notification to be dismissed from the status bar. Do Figure 2-27
- 99. Displaying Notifications ❘ 77 How It Works To display a notification, you first created an Intent object to point to the NotificationView class: //---PendingIntent to launch activity if the user selects // this notification--- Intent i = new Intent(this, NotificationView.class); i.putExtra(“notificationID”, notificationID); This intent will be used to launch another activity when the user selects a notification from the list of noti- fications. In this example, you added a key/value pair to the Intent object so that you can tag the notifica- tion ID, identifying the notification to the target activity. This ID will be used to dismiss the notifications later. You would also need to create a PendingIntent object. A PendingIntent object helps you to perform an action on your application’s behalf, often at a later time, regardless of whether your application is run- ning or not. In this case, you initialized it as follows: PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, i, 0); The getActivity() method retrieves a PendingIntent object and you set it using the following arguments: ➤➤ context — Application context ➤➤ request code — Request code for the intent ➤➤ intent — The intent for launching the target activity ➤➤ flags — The flags in which the activity is to be launched You then obtain an instance of the NotificationManager class and create an instance of the Notification class: NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE); Notification notif = new Notification( R.drawable.icon, “Reminder: Meeting starts in 5 minutes”, System.currentTimeMillis()); The Notification class enables you to specify the notification’s main information when the notification first appears on the status bar. The second argument to the Notification constructor sets the “ticker text” on the status bar (see Figure 2-28). Figure 2-28
- 100. 78 ❘ Chapter 2 Activities and Intents Next, you set the details of the notification using the setLatestEventInfo() method: CharSequence from = “System Alarm”; CharSequence message = “Meeting with customer at 3pm...”; notif.setLatestEventInfo(this, from, message, pendingIntent); //---100ms delay, vibrate for 250ms, pause for 100 ms and // then vibrate for 500ms--- notif.vibrate = new long[] { 100, 250, 100, 500}; The preceding also sets the notification to vibrate the phone. Finally, to display the notification you use the notify() method: nm.notify(notificationID, notif); When the user clicks on the notification, the NotificationView activity is launched. Here, you dismiss the notification by using the cancel() method of the NotificationManager object and passing it the ID of the notification (passed in via the Intent object): //---look up the notification manager service--- NotificationManager nm = (NotificationManager) getSystemService(NOTIFICATION_SERVICE); //---cancel the notification that we started nm.cancel(getIntent().getExtras().getInt(“notificationID”)); Summary This chapter first provided a detailed look at how activities work and the various forms in which you can display them. You also learned how to display dialog windows using activities. The second part of this chapter demonstrated a very important concept in Android — the intent. The intent is the “glue” that enables different activities to be connected, and is a vital concept to under- stand when developing for the Android platform. Exercises 1 . What will happen if you have two or more activities with the same intent filter action name? 2 . Write the code to invoke the built-in Browser application. 3. Which components can you specify in an intent filter? 4. What is the difference between the Toast and NotificationManager class? Answers to the Exercises can be found in Appendix C.
- 101. Summary ❘ 79 ⊲⊲ What You Learned In This Chapter Topic Key Concepts Creating an activity All activities must be declared in the AndroidManifest.xml file. Key life cycle of an activity When an activity is started, the onStart() and onResume() events are always called. When an activity is killed or sent to the background, the onPause() event is always called. Displaying an activity as a Use the showDialog() method and implement the onCreate dialog Dialog() method. Intent The “glue” that connects different activities Intent filter The “filter” that enables you to specify how your activities should be called Calling an activity Use the startActivity() or startActivityForResult() method. Passing data to an activity Use the Bundle object. Components in an Intent An Intent object can contain the following: action, data, type, and object category. Displaying notifications Use the NotificationManager class. PendingIntent object A PendingIntent object helps you to perform an action on your application’s behalf, often at a later time, regardless of whether or not your application is running.
- 103. 3 getting to Know the Android User interface WhAt you Will leArn in thiS chApter ➤➤ The various ViewGroups you can use to lay out your views ➤➤ How to adapt to changes in screen orientation ➤➤ How to manage screen orientation changes ➤➤ How to create the UI programmatically ➤➤ How to listen for UI notifications In Chapter 2, you learned about the Activity class and its life cycle. You learned that an activity is a means by which users interact with the application. However, an activity by itself does not have a presence on the screen. Instead, it has to draw the screen using Views and ViewGroups. In this chapter, you will learn the details about creating user interfaces in Android, how users inter- act with them. In addition, you will learn how to handle changes in screen orientation on your Android devices. underStAnding the componentS oF A Screen In Chapter 2, you saw that the basic unit of an Android application is an activity. An activity displays the user interface of your application, which may contain widgets like buttons, labels, text boxes, and so on. Typically, you defi ne your UI using an XML fi le (e.g., the main.xml fi le located in the res/layout folder), which may look like this: <?xmlversion=”1.0”encoding=”utf-8”?> <LinearLayoutxmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical”
- 104. 82 ❘ chApter 3 GettinG to Know the android USer interface android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”@string/hello” /> </LinearLayout> During run time, you load the XML UI in the onCreate() event handler in your Activity class, using the setContentView() method of the Activity class: @Override publicvoidonCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.main); } During compilation, each element in the XML fi le is compiled into its equivalent Android GUI class, with attributes represented by methods. The Android system then creates the UI of the activity when it is loaded. NOTE While it is always easier to build your UI using an XML file, sometimes you need to build your UI dynamically during run time (for example, when writing games). Hence, it is also possible to create your UI entirely using code. Later in this chapter you will see an example of how this can be done. views and viewgroups An activity contains Views and ViewGroups. A view is a widget that has an appearance on screen. Examples of views are buttons, labels, and text boxes. A view derives from the base class android .view.View. NOTE Chapters 4 and 5 discuss the various common views in Android. One or more views can be grouped together into a ViewGroup. A ViewGroup (which is itself a spe- cial type of view) provides the layout in which you can order the appearance and sequence of views. Examples of ViewGroups include LinearLayout and FrameLayout. A ViewGroup derives from the base class android.view.ViewGroup. Android supports the following ViewGroups: ➤➤ LinearLayout ➤➤ AbsoluteLayout
- 105. Understanding the Components of a Screen ❘ 83 ➤➤ TableLayout ➤➤ RelativeLayout ➤➤ FrameLayout ➤➤ ScrollView The following sections describe each of these ViewGroups in more detail. Note that in practice it is common to combine different types of layouts to create the UI you want. LinearLayout The LinearLayout arranges views in a single column or a single row. Child views can be arranged either vertically or horizontally. To see how LinearLayout works, consider the following elements typically contained in the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”@string/hello” /> </LinearLayout> In the main.xml file, observe that the root element is <LinearLayout> and it has a <TextView> ele- ment contained within it. The <LinearLayout> element controls the order in which the views con- tained within it appear. Each View and ViewGroup has a set of common attributes, some of which are described in Table 3-1. Table 3-1: Common Attributes Used in Views and ViewGroups Attribute Description layout_width Specifies the width of the View or ViewGroup layout_height Specifies the height of the View or ViewGroup layout_marginTop Specifies extra space on the top side of the View or ViewGroup layout_marginBottom Specifies extra space on the bottom side of the View or ViewGroup layout_marginLeft Specifies extra space on the left side of the View or ViewGroup layout_marginRight Specifies extra space on the right side of the View or ViewGroup continues
- 106. 84 ❘ chApter 3 GettinG to Know the android USer interface tABle 3-1 (continued) AttriBute deScription layout_gravity Specifies how child Views are positioned layout_weight Specifies how much of the extra space in the layout should be allocated to the View layout_x Specifies the x-coordinate of the View or ViewGroup layout_y Specifies the y-coordinate of the View or ViewGroup NOTE Some of these attributes are applicable only when a View is in a specific ViewGroup. For example, the layout_weight and layout_gravity attributes are applicable only when a View is in either a LinearLayout or a TableLayout. For example, the width of the <TextView> element fi lls the entire width of its parent (which is the screen in this case) using the fill_parent constant. Its height is indicated by the wrap_content con- stant, which means that its height is the height of its content (in this case, the text contained within it). If you don’t want to have the <TextView> view occupy the entire row, you can set its layout_width attribute to wrap_content, like this: <TextView android:layout_width=”wrap_content android:layout_height=”wrap_content” android:text=”@string/hello” /> This will set the width of the view to be equal to the width of the text contained within it. Consider the following layout: <?xmlversion=”1.0”encoding=”utf-8”?> <LinearLayoutxmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”105dp” android:layout_height=”wrap_content” android:text=”@string/hello” /> <Button android:layout_width=”160dp” android:layout_height=”wrap_content” android:text=”Button” /> </LinearLayout>
- 107. Understanding the Components of a Screen ❘ 85 unitS oF meASurement When specifying the size of an element on an Android UI, you should be aware of the following units of measurement: ➤➤ dp — Density-independent pixel. 160dp is equivalent to one inch of physical screen size. This is the recommended unit of measurement when specifying the dimension of views in your layout. You can specify either “dp” or “dip” when referring to a density-independent pixel. ➤➤ sp — Scale-independent pixel. This is similar to dpand is recommended for specifying font sizes. ➤➤ pt — Point. A point is defined to be 1/72 of an inch, based on the physical screen size. ➤➤ px — Pixel. Corresponds to actual pixels on the screen. Using this unit is not recommended, as your UI may not render correctly on devices with different screen sizes. Here, you set the width of both the TextView and Button views to an absolute value. In this case, the width for the TextView is set to 105 density-independent pixels wide, and the Button to 160 density- independent pixels wide. Figure 3-1 shows how the views look when viewed on an emulator with a resolution of 320×480. Figure 3-2 shows how the views look when viewed on a high-resolution (480×800) emulator. Figure 3-1 Figure 3-2 As you can see, in both emulators the widths of both views are the same with respect to the width of the emulator. This demonstrates the usefulness of using the dp unit, which ensures that even if the reso- lution of the target device is different, the size of the view relative to the device remains unchanged.
- 108. 86 ❘ Chapter 3 Getting to Know the Android User Interface The preceding example also specifies that the orientation of the layout is vertical: <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > The default orientation layout is horizontal, so if you omit the android:orientation attribute, the views will appear as shown in Figure 3-3. Figure 3-3 In LinearLayout, you can apply the layout_weight and layout_gravity attributes to views con- tained within it, as the following modifications to main.xml show: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”105dp” android:layout_height=”wrap_content” android:text=”@string/hello” /> <Button android:layout_width=”160dp” android:layout_height=”wrap_content” android:text=”Button”
- 109. Understanding the Components of a Screen ❘ 87 android:layout_gravity=”right” android:layout_weight=”0.2” /> <EditText android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:textSize=”18sp” android:layout_weight=”0.8” /> </LinearLayout> Figure 3-4 shows that the button is aligned to the right of its parent (which is the LinearLayout) using the layout_gravity attribute. At the same time, you use the layout_weight attribute to spec- ify the ratio in which the Button and EditText views occupy the remaining space on the screen. The total value for the layout_weight attribute must be equal to 1. Figure 3-4 AbsoluteLayout The AbsoluteLayout enables you to specify the exact location of its children. Consider the following UI defined in main.xml: <?xml version=”1.0” encoding=”utf-8”?> <AbsoluteLayout android:layout_width=”fill_parent” android:layout_height=”fill_parent” xmlns:android=”http://schemas.android.com/apk/res/android”
- 110. 88 ❘ Chapter 3 Getting to Know the Android User Interface > <Button android:layout_width=”188dp” android:layout_height=”wrap_content” android:text=”Button” android:layout_x=”126px” android:layout_y=”361px” /> <Button android:layout_width=”113dp” android:layout_height=”wrap_content” android:text=”Button” android:layout_x=”12px” android:layout_y=”361px” /> </AbsoluteLayout> Figure 3-5 shows the two Button views located at their specified positions using the android_layout_x and android_layout_y attributes. Figure 3-5 However, there is a problem with the AbsoluteLayout when the activity is viewed on a high-resolu- tion screen (see Figure 3-6). For this reason, the AbsoluteLayout has been deprecated since Android 1.5 (although it is still supported in the current version). You should avoid using the AbsoluteLayout in your UI, as it is not guaranteed to be supported in future versions of Android. You should instead use the other layouts described in this chapter.
- 111. Understanding the Components of a Screen ❘ 89 Figure 3-6 TableLayout The TableLayout groups views into rows and columns. You use the <TableRow> element to designate a row in the table. Each row can contain one or more views. Each view you place within a row forms a cell. The width of each column is determined by the largest width of each cell in that column. Consider the content of main.xml shown here: <?xml version=”1.0” encoding=”utf-8”?> <TableLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:layout_height=”fill_parent” android:layout_width=”fill_parent” > <TableRow> <TextView android:text=”User Name:” android:width =”120px” /> <EditText android:id=”@+id/txtUserName” android:width=”200px” /> </TableRow>
- 112. 90 ❘ Chapter 3 Getting to Know the Android User Interface <TableRow> <TextView android:text=”Password:” /> <EditText android:id=”@+id/txtPassword” android:password=”true” /> </TableRow> <TableRow> <TextView /> <CheckBox android:id=”@+id/chkRememberPassword” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Remember Password” /> </TableRow> <TableRow> <Button android:id=”@+id/buttonSignIn” android:text=”Log In” /> </TableRow> </TableLayout> Figure 3-7 shows what the preceding looks like when rendered on the Android Emulator. Figure 3-7 Note that in the preceding example, there are two columns and four rows in the TableLayout. The cell directly under the Password TextView is populated with an <TextView/> empty element. If you don’t do this, the Remember Password checkbox will appear under the Password TextView, as shown in Figure 3-8.
- 113. Understanding the Components of a Screen ❘ 91 Figure 3-8 RelativeLayout The RelativeLayout enables you to specify how child views are positioned relative to each other. Consider the following main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <RelativeLayout android:id=”@+id/RLayout” android:layout_width=”fill_parent” android:layout_height=”fill_parent” xmlns:android=”http://schemas.android.com/apk/res/android” > <TextView android:id=”@+id/lblComments” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Comments” android:layout_alignParentTop=”true” android:layout_alignParentLeft=”true” /> <EditText android:id=”@+id/txtComments” android:layout_width=”fill_parent” android:layout_height=”170px” android:textSize=”18sp” android:layout_alignLeft=”@+id/lblComments” android:layout_below=”@+id/lblComments” android:layout_centerHorizontal=”true” /> <Button android:id=”@+id/btnSave”
- 114. 92 ❘ Chapter 3 Getting to Know the Android User Interface android:layout_width=”125px” android:layout_height=”wrap_content” android:text=”Save” android:layout_below=”@+id/txtComments” android:layout_alignRight=”@+id/txtComments” /> <Button android:id=”@+id/btnCancel” android:layout_width=”124px” android:layout_height=”wrap_content” android:text=”Cancel” android:layout_below=”@+id/txtComments” android:layout_alignLeft=”@+id/txtComments” /> </RelativeLayout> Notice that each view embedded within the RelativeLayout has attributes that enable it to align with another view. These attributes are as follows: ➤➤ layout_alignParentTop ➤➤ layout_alignParentLeft ➤➤ layout_alignLeft ➤➤ layout_alignRight ➤➤ layout_below ➤➤ layout_centerHorizontal The value for each of these attributes is the ID for the view that you are referencing. The preceding XML UI creates the screen shown in Figure 3-9. Figure 3-9
- 115. Understanding the Components of a Screen ❘ 93 Framelayout The FrameLayout is a placeholder on screen that you can use to display a single view. Views that you add to a FrameLayout are always anchored to the top left of the layout. Consider the following con- tent in main.xml: <?xmlversion=”1.0”encoding=”utf-8”?> <RelativeLayout android:id=”@+id/RLayout” android:layout_width=”fill_parent” android:layout_height=”fill_parent” xmlns:android=”http://schemas.android.com/apk/res/android” > <TextView android:id=”@+id/lblComments” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Thisismylovelydog,Ookii” android:layout_alignParentTop=”true” android:layout_alignParentLeft=”true” /> <FrameLayout android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:layout_alignLeft=”@+id/lblComments” android:layout_below=”@+id/lblComments” android:layout_centerHorizontal=”true” > <ImageView android:src=“@drawable/ookii” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> </FrameLayout> </RelativeLayout> Here, you have a FrameLayout within a RelativeLayout. Within the FrameLayout, you embed an ImageView. The UI is shown in Figure 3-10. NOTE This example assumes that the res/drawable-mdpi folder has an image named ookii.png. If you add another view (such as a Button view) within the FrameLayout, the view will overlap the previous view (see Figure 3-11): <?xmlversion=”1.0”encoding=”utf-8”?> <RelativeLayout android:id=”@+id/RLayout” android:layout_width=”fill_parent” android:layout_height=”fill_parent”
- 116. 94 ❘ Chapter 3 Getting to Know the Android User Interface xmlns:android=”http://schemas.android.com/apk/res/android” > <TextView android:id=”@+id/lblComments” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”This is my lovely dog, Ookii” android:layout_alignParentTop=”true” android:layout_alignParentLeft=”true” /> <FrameLayout android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:layout_alignLeft=”@+id/lblComments” android:layout_below=”@+id/lblComments” android:layout_centerHorizontal=”true” > <ImageView android:src = “@drawable/ookii” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> <Button android:layout_width=”124dp” android:layout_height=”wrap_content” android:text=”Print Picture” /> </FrameLayout> </RelativeLayout> Figure 3-10
- 117. Understanding the Components of a Screen ❘ 95 Figure 3-11 NOTE You can add multiple views to a FrameLayout, but each will be stacked on top of the previous one. This is useful in cases where you want to animate series of images, with only one visible at a time. Scrollview A ScrollView is a special type of FrameLayout in that it enables users to scroll through a list of views that occupy more space than the physical display. The ScrollView can contain only one child view or ViewGroup, which normally is a LinearLayout. NOTE Do not use a ListView (discussed in Chapter 4) together with the ScrollView. The ListView is designed for showing a list of related information and is optimized for dealing with large lists. The following main.xml content shows a ScrollView containing a LinearLayout, which in turn contains some Button and EditText views: <?xmlversion=”1.0”encoding=”utf-8”?> <ScrollView android:layout_width=”fill_parent”
- 118. 96 ❘ Chapter 3 Getting to Know the Android User Interface android:layout_height=”fill_parent” xmlns:android=”http://schemas.android.com/apk/res/android” > <LinearLayout android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:orientation=”vertical” > <Button android:id=”@+id/button1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Button 1” /> <Button android:id=”@+id/button2” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Button 2” /> <Button android:id=”@+id/button3” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Button 3” /> <EditText android:id=”@+id/txt” android:layout_width=”fill_parent” android:layout_height=”300px” /> <Button android:id=”@+id/button4” Do android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Button 4” /> <Button android:id=”@+id/button5” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Button 5” /> </LinearLayout> </ScrollView> Figure 3-12 shows the ScrollView enabling the users to drag the screen upward to reveal the views located at the bottom of the screen.
- 119. Adapting to Display Orientation ❘ 97 Figure 3-12 AdApting to diSplAy orientAtion One of the key features of modern smartphones is their ability to switch screen orientation, and Android is no exception. Android supports two screen orientations: portrait and landscape. By default, when you change the display orientation of your Android device, the current activity that is displayed will automatically redraw its content in the new orientation. This is because the onCreate() event of the activity is fi red whenever there is a change in display orientation. NOTE When you change the orientation of your Android device, your current activity is actually destroyed and then re-created. However, when the views are redrawn, they may be drawn in their original locations (depending on the layout selected). Figure 3-13 shows one of the examples illustrated earlier displayed in both por- trait and landscape mode. As you can observe in landscape mode, a lot of empty space on the right of the screen could be used. Furthermore, any additional views at the bottom of the screen would be hidden when the screen ori- entation is set to landscape.
- 120. 98 ❘ Chapter 3 Getting to Know the Android User Interface Figure 3-13 In general, you can employ two techniques to handle changes in screen orientation: ➤➤ Anchoring — The easiest way is to “anchor” your views to the four edges of the screen. When the screen orientation changes, the views can anchor neatly to the edges. ➤➤ Resizing and repositioning — Whereas anchoring and centralizing are simple techniques to ensure that views can handle changes in screen orientation, the ultimate technique is resizing each and every view according to the current screen orientation. Anchoring Views Anchoring could be easily achieved by using RelativeLayout. Consider the following main.xml containing five Button views embedded within the <RelativeLayout> element: <?xml version=”1.0” encoding=”utf-8”?> <RelativeLayout android:layout_width=”fill_parent” android:layout_height=”fill_parent” xmlns:android=”http://schemas.android.com/apk/res/android” > <Button android:id=”@+id/button1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Top Left Button” android:layout_alignParentLeft=”true” android:layout_alignParentTop=”true” />
- 121. Adapting to Display Orientation ❘ 99 <Button android:id=”@+id/button2” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Top Right Button” android:layout_alignParentTop=”true” android:layout_alignParentRight=”true” /> <Button android:id=”@+id/button3” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Bottom Left Button” android:layout_alignParentLeft=”true” android:layout_alignParentBottom=”true” /> <Button android:id=”@+id/button4” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Bottom Right Button” android:layout_alignParentRight=”true” android:layout_alignParentBottom=”true” /> <Button android:id=”@+id/button5” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Middle Button” android:layout_centerVertical=”true” android:layout_centerHorizontal=”true” /> </RelativeLayout> Observe the following attributes found in the various Button views: ➤➤ layout_alignParentLeft — Aligns the view to the left of the parent view ➤➤ layout_alignParentRight — Aligns the view to the right of the parent view ➤➤ layout_alignParentTop — Aligns the view to the top of the parent view ➤➤ layout_alignParentBottom — Aligns the view to the bottom of the parent view ➤➤ layout_centerVertical — Centers the view vertically within its parent view ➤➤ layout_centerHorizontal — Centers the view horizontally within its parent view Figure 3-14 shows the activity when viewed in portrait mode. When the screen orientation changes to landscape mode, the four buttons are aligned to the four edges of the screen, and the center button is centered in the middle of the screen with its width fully stretched (see Figure 3-15).
- 122. 100 ❘ Chapter 3 Getting to Know the Android User Interface Figure 3-14 Figure 3-15
- 123. Adapting to Display Orientation ❘ 101 Resizing and Repositioning Apart from anchoring your views to the four edges of the screen, an easier way to customize the UI based on screen orientation is to create a separate res/layout folder containing the XML files for the UI of each orientation. To support land- scape mode, you can create a new folder in the res folder and name it as layout-land (representing landscape). Figure 3-16 shows the new folder containing the file main.xml. Basically, the main.xml file contained within the layout folder defines the UI for the activity in portrait mode, whereas the main.xml file in the layout-land Figure 3-16 folder defines the UI in landscape mode. The following shows the content of main.xml under the layout folder: <?xml version=”1.0” encoding=”utf-8”?> <RelativeLayout android:layout_width=”fill_parent” android:layout_height=”fill_parent” xmlns:android=”http://schemas.android.com/apk/res/android” > <Button android:id=”@+id/button1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Top Left Button” android:layout_alignParentLeft=”true” android:layout_alignParentTop=”true” /> <Button android:id=”@+id/button2” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Top Right Button” android:layout_alignParentTop=”true” android:layout_alignParentRight=”true” /> <Button android:id=”@+id/button3” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Bottom Left Button” android:layout_alignParentLeft=”true” android:layout_alignParentBottom=”true” /> <Button android:id=”@+id/button4” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Bottom Right Button” android:layout_alignParentRight=”true” android:layout_alignParentBottom=”true” />
- 124. 102 ❘ Chapter 3 Getting to Know the Android User Interface <Button android:id=”@+id/button5” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Middle Button” android:layout_centerVertical=”true” android:layout_centerHorizontal=”true” /> </RelativeLayout> The following shows the content of main.xml under the layout-land folder (the statements in bold are the additional views to display in landscape mode): <?xml version=”1.0” encoding=”utf-8”?> <RelativeLayout android:layout_width=”fill_parent” android:layout_height=”fill_parent” xmlns:android=”http://schemas.android.com/apk/res/android” > <Button android:id=”@+id/button1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Top Left Button” android:layout_alignParentLeft=”true” android:layout_alignParentTop=”true” /> <Button android:id=”@+id/button2” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Top Right Button” android:layout_alignParentTop=”true” android:layout_alignParentRight=”true” /> <Button android:id=”@+id/button3” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Bottom Left Button” android:layout_alignParentLeft=”true” android:layout_alignParentBottom=”true” /> <Button android:id=”@+id/button4” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Bottom Right Button” android:layout_alignParentRight=”true” android:layout_alignParentBottom=”true” /> <Button android:id=”@+id/button5” android:layout_width=”fill_parent”
- 125. Adapting to Display Orientation ❘ 103 android:layout_height=”wrap_content” android:text=”Middle Button” android:layout_centerVertical=”true” android:layout_centerHorizontal=”true” /> <Button android:id=”@+id/button6” android:layout_width=”180px” android:layout_height=”wrap_content” android:text=”Top Middle Button” android:layout_centerVertical=”true” android:layout_centerHorizontal=”true” android:layout_alignParentTop=”true” /> <Button android:id=”@+id/button7” android:layout_width=”180px” android:layout_height=”wrap_content” android:text=”Bottom Middle Button” android:layout_centerVertical=”true” android:layout_centerHorizontal=”true” android:layout_alignParentBottom=”true” /> </RelativeLayout> When the activity is loaded in portrait mode, it will show five buttons, as shown in Figure 3-17. Figure 3-17
- 126. 104 ❘ Chapter 3 Getting to Know the Android User Interface When the activity is loaded in landscape mode, there are now seven buttons (see Figure 3-18), proving that different XML files are loaded when the device is in a different orientation. Figure 3-18 Using this method, when the orientation of the device changes, Android will automatically load the appropriate XML file for your activity depending on the current screen orientation. Managing Changes to Screen Orientation Now that you have looked at how to implement the two techniques for adapting to screen orienta- tion changes, let’s explore what happens to an activity’s state when the device changes orientation. The following Try It Out demonstrates the behavior of an activity when the device changes orientation. Try It Out Understanding Activity Behavior When Orientation Changes codefile Orientations.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it Orientations. 2 . Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android”
- 127. Managing Changes to Screen Orientation ❘ 105 android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <EditText android:id=”@+id/txtField1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <EditText android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> </LinearLayout> 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Orientations; import android.app.Activity; import android.os.Bundle; import android.util.Log; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Log.d(“StateInfo”, “onCreate”); } @Override public void onStart() { Log.d(“StateInfo”, “onStart”); super.onStart(); } @Override public void onResume() { Log.d(“StateInfo”, “onResume”); super.onResume(); } @Override public void onPause() { Log.d(“StateInfo”, “onPause”); super.onPause(); } @Override public void onStop() { Log.d(“StateInfo”, “onStop”); super.onStop(); }
- 128. 106 ❘ Chapter 3 Getting to Know the Android User Interface @Override public void onDestroy() { Log.d(“StateInfo”, “onDestroy”); super.onDestroy(); } @Override public void onRestart() { Log.d(“StateInfo”, “onRestart”); super.onRestart(); } } 4 . Press F11 to debug the application on the Android Emulator. 5. Enter some text into the two EditText views (see Figure 3-19). 6. Change the orientation of the Android Emulator by pressing Ctrl+F11. Figure 3-20 shows the emu- lator in landscape mode. Note that the text in the first EditText view is still visible, while the second EditText view is now empty. 7. Observe the output in the LogCat window (you need to switch to the Debug perspective in Eclipse). You should see something like this: 01-05 13:32:30.266: DEBUG/StateInfo(5477): onCreate 01-05 13:32:30.296: DEBUG/StateInfo(5477): onStart 01-05 13:32:30.296: DEBUG/StateInfo(5477): onResume ... 01-05 13:35:20.106: DEBUG/StateInfo(5477): onPause 01-05 13:35:20.106: DEBUG/StateInfo(5477): onStop 01-05 13:35:20.106: DEBUG/StateInfo(5477): onDestroy 01-05 13:35:20.246: DEBUG/StateInfo(5477): onCreate 01-05 13:35:20.256: DEBUG/StateInfo(5477): onStart 01-05 13:35:20.256: DEBUG/StateInfo(5477): onResume How It Works From the output shown in the LogCat window, it is apparent that when the device changes orientation, the activity is destroyed: 01-05 13:35:20.106: DEBUG/StateInfo(5477): onPause 01-05 13:35:20.106: DEBUG/StateInfo(5477): onStop 01-05 13:35:20.106: DEBUG/StateInfo(5477): onDestroy It is then re-created: 01-05 13:35:20.246: DEBUG/StateInfo(5477): onCreate 01-05 13:35:20.256: DEBUG/StateInfo(5477): onStart 01-05 13:35:20.256: DEBUG/StateInfo(5477): onResume It is important that you understand this behavior because you need to ensure that you take the neces- sary steps to preserve the state of your activity before it changes orientation. For example, you may have variables containing values needed for some calculations in the activity. For any activity, you should save whatever state you need to save in the onPause() event, which is fired every time the activity changes ori- entation. The following section demonstrates the different ways to save this state information.
- 129. Managing Changes to Screen Orientation ❘ 107 Figure 3-19 Figure 3-20
- 130. 108 ❘ Chapter 3 Getting to Know the Android User Interface Another important behavior to understand is that only views that are named (via the android:id attri- bute) in an activity will have their state persisted when the activity they are contained in is destroyed. For example, the user may change orientation while entering some text into an EditText view. When this happens, any text inside the EditText view will be persisted and restored automatically when the activity is re-created. In contrast, if you do not name the EditText view using the android:id attribute, the activity will not be able to persist the text currently contained within it. Persisting State Information during Changes in Configuration So far, you have learned that changing screen orientation destroys an activity and re-creates it. Keep in mind that when an activity is re-created, the current state of the activity may be lost. When an activity is killed, it will fire one or more of the following two events: ➤➤ onPause() — This event is always fired whenever an activity is killed or pushed into the background. ➤➤ onSaveInstanceState() — This event is also fired whenever an activity is about to be killed or put into the background (just like the onPause() event). However, unlike the onPause() event, the onSaveInstanceState event is not fired when an activity is being unloaded from the stack (for example, when the user pressed the Back button), because there is no need to restore its state later. In short, to preserve the state of an activity, you could always implement the onPause() event, and then use your own ways to preserve the state of your activity, such as using a database, internal or external file storage, etc. If you simply want to preserve the state of an activity so that it can be restored later when the activity is re-created (such as when the device changes orientation), a much simpler way would be to imple- ment the onSaveInstanceState() method, as it provides a Bundle object as an argument so that you can use it to save your activity’s state. The following code shows that you can save the string ID into the Bundle object during the onSaveInstanceState event: @Override public void onSaveInstanceState(Bundle outState) { //---save whatever you need to persist--- outState.putString(“ID”, “1234567890”); super.onSaveInstanceState(outState); } When an activity is re-created, the onCreate() event is first fired, followed by the onRestoreInstanceState() event, which enables you to retrieve the state that you saved previously in the onSaveInstanceState event through the Bundle object in its argument: @Override public void onRestoreInstanceState(Bundle savedInstanceState) { super.onRestoreInstanceState(savedInstanceState); //---retrieve the information persisted earlier--- String ID = savedInstanceState.getString(“ID”); }
- 131. Managing Changes to Screen Orientation ❘ 109 Although you can use the onSaveInstanceState() event to save state information, note the limitation that you can only save your state information into a Bundle object. If you need to save more complex data structures, then this is not an adequate solution. Another event handler that you can use is the onRetainNonConfigurationInstance() event. This event is fi red when an activity is about to be destroyed due to a configuration change. You can save your current data by returning it in this event, like this: @Override publicObjectonRetainNonConfigurationInstance(){ //---savewhateveryouwanthere;ittakesinanObjecttype--- return(“Sometexttopreserve”); } NOTE When screen orientation changes, this change is part of what is known as a configuration change. A configuration change will cause your current activ- ity to be destroyed. Note that this event returns an Object type, which pretty much allows you to return any data type. To extract the saved data, you can extract it in the onCreate() event, using the getLastNonConfigurationInstance() method, like this: @Override publicvoidonCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.main); Log.d(“StateInfo”,“onCreate”); String str = (String) getLastNonConfigurationInstance(); } detecting orientation changes Sometimes you need to know the device’s current orientation during run time. To determine that, you can use the WindowManager class. The following code snippet demonstrates how you can pro- grammatically detect the current orientation of your activity: import android.util.Log; import android.view.Display; import android.view.WindowManager; //... publicvoidonCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.main); //---getthecurrentdisplayinfo--- WindowManager wm = getWindowManager(); Display d = wm.getDefaultDisplay(); if (d.getWidth() > d.getHeight())
- 132. 110 ❘ Chapter 3 Getting to Know the Android User Interface { //---landscape mode--- Log.d(“Orientation”, “Landscape mode”); } else { //---portrait mode--- Log.d(“Orientation”, “Portrait mode”); } } The getDefaultDisplay() method returns a Display object representing the screen of the device. You can then get its width and height and deduce the current orientation. Controlling the Orientation of the Activity Occasionally you might want to ensure that your application is only displayed in a certain orienta- tion. For example, you may be writing a game that should only be viewed in landscape mode. In this case, you can programmatically force a change in orientation using the setRequestOrientation() method of the Activity class: import android.content.pm.ActivityInfo; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---change to landscape mode--- setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE); } To change to portrait mode, use the ActivityInfo.SCREEN_ORIENTATION_PORTRAIT constant: setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT); Besides using the setRequestOrientation() method, you can also use the android:screenOrientation attribute on the <activity> element in AndroidManifest.xml as follows to constrain the activity to a certain orientation: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Orientations” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name” android:screenOrientation=”landscape” > <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter>
- 133. Creating the User Interface Programmatically ❘ 111 </activity> </application> <uses-sdk android:minSdkVersion=”9” /> </manifest> The preceding example constrains the activity to a certain orientation (landscape in this case) and pre- vents the activity from being destroyed; that is, the activity will not be destroyed and the onCreate() event will not be fired again when the orientation of the device changes. Following are two other values that you can specify in the android:screenOrientation attribute: ➤➤ portrait — Portrait mode ➤➤ sensor — Based on the accelerometer Creating the User Interface Programmatically So far, all the UIs you have seen in this chapter are created using XML. As mentioned earlier, besides using XML you can also create the UI using code. This approach is useful if your UI needs to be dynami- cally generated during run time. For example, suppose you are building a cinema ticket reservation sys- tem and your application will display the seats of each cinema using buttons. In this case, you would need to dynamically generate the UI based on the cinema selected by the user. The following Try It Out demonstrates the code needed to dynamically build the UI in your activity. Try It Out Creating the UI via Code codefile UICode.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it UICode. 2 . In the MainActivity.java file, add the following statements in bold: package net.learn2develop.UICode; import android.app.Activity; import android.os.Bundle; import android.view.ViewGroup.LayoutParams; import android.widget.Button; import android.widget.LinearLayout; import android.widget.TextView; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //setContentView(R.layout.main); //---param for views--- LayoutParams params =
- 134. 112 ❘ Chapter 3 Getting to Know the Android User Interface new LinearLayout.LayoutParams( LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT); //---create a layout--- LinearLayout layout = new LinearLayout(this); layout.setOrientation(LinearLayout.VERTICAL); //---create a textview--- TextView tv = new TextView(this); tv.setText(“This is a TextView”); tv.setLayoutParams(params); //---create a button--- Button btn = new Button(this); btn.setText(“This is a Button”); btn.setLayoutParams(params); //---adds the textview--- layout.addView(tv); //---adds the button--- layout.addView(btn); //---create a layout param for the layout--- LinearLayout.LayoutParams layoutParam = new LinearLayout.LayoutParams( LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT ); this.addContentView(layout, layoutParam); } } 3 . Press F11 to debug the application on the Android Emulator. Figure 3-21 shows the activity created. How It Works In this example, you first commented out the setContentView() statement so that it does not load the UI from the main.xml file. You then created a LayoutParams object to specify the layout parameter that can be used by other views (which you will create next): //---param for views--- LayoutParams params = new LinearLayout.LayoutParams( LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT); You also created a LinearLayout object to contain all the views in your activity: //---create a layout--- LinearLayout layout = new LinearLayout(this); layout.setOrientation(LinearLayout.VERTICAL);
- 135. Creating the User Interface Programmatically ❘ 113 Figure 3-21 Next, you created a TextView and a Button view: //---create a textview--- TextView tv = new TextView(this); tv.setText(“This is a TextView”); tv.setLayoutParams(params); //---create a button--- Button btn = new Button(this); btn.setText(“This is a Button”); btn.setLayoutParams(params); You then added them to the LinearLayout object: //---adds the textview--- layout.addView(tv); //---adds the button--- layout.addView(btn); You also created a LayoutParams object to be used by the LinearLayout object: //---create a layout param for the layout--- LinearLayout.LayoutParams layoutParam = new LinearLayout.LayoutParams( LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT );
- 136. 114 ❘ Chapter 3 Getting to Know the Android User Interface Finally, you added the LinearLayout object to the activity: this.addContentView(layout, layoutParam); As you can see, using code to create the UI is quite a laborious affair. Hence, dynamically generate your UI using code only when necessary. Listening for UI Notifications Users interact with your UI at two levels: the activity level and the views level. At the activity level, the Activity class exposes methods that you can override. Some common methods that you can override in your activities include the following: ➤➤ onKeyDown — Called when a key was pressed and not handled by any of the views contained within the activity ➤➤ onKeyUp — Called when a key was released and not handled by any of the views contained within the activity ➤➤ onMenuItemSelected — Called when a panel’s menu item has been selected by the user (cov- ered in Chapter 5) ➤➤ onMenuOpened — Called when a panel’s menu is opened by the user (covered in Chapter 5) Overriding Methods Defined in an Activity To understand how activities interact with the user, let’s start off by overriding some of the methods defined in the activity’s base class and learn how they are handled when the user interacts with the Do activity. Try It Out Overriding Activity Methods codefile UIActivity.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it UIActivity. 2 . Add the following statements in bold: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:orientation=”vertical” xmlns:android=”http://schemas.android.com/apk/res/android” > <TextView android:layout_width=”214dp”
- 137. Listening for UI Notifications ❘ 115 android:layout_height=”wrap_content” android:text=”Your Name” /> <EditText android:id=”@+id/txt1” android:layout_width=”214dp” android:layout_height=”wrap_content” /> <Button android:id=”@+id/btn1” android:layout_width=”106dp” android:layout_height=”wrap_content” android:text=”OK” /> <Button android:id=”@+id/btn2” android:layout_width=”106dp” android:layout_height=”wrap_content” android:text=”Cancel” /> </LinearLayout> 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.UIActivity; import android.app.Activity; import android.os.Bundle; import android.view.KeyEvent; import android.widget.Toast; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { switch (keyCode) { case KeyEvent.KEYCODE_DPAD_CENTER: Toast.makeText(getBaseContext(), “Center was clicked”, Toast.LENGTH_LONG).show(); break; case KeyEvent.KEYCODE_DPAD_LEFT: Toast.makeText(getBaseContext(), “Left arrow was clicked”,
- 138. 116 ❘ Chapter 3 Getting to Know the Android User Interface Toast.LENGTH_LONG).show(); break; case KeyEvent.KEYCODE_DPAD_RIGHT: Toast.makeText(getBaseContext(), “Right arrow was clicked”, Toast.LENGTH_LONG).show(); break; case KeyEvent.KEYCODE_DPAD_UP: Toast.makeText(getBaseContext(), “Up arrow was clicked”, Toast.LENGTH_LONG).show(); break; case KeyEvent.KEYCODE_DPAD_DOWN: Toast.makeText(getBaseContext(), “Down arrow was clicked”, Toast.LENGTH_LONG).show(); break; } return false; } } 4 . Press F11 to debug the application on the Android Emulator. 5. When the activity is loaded, type some text into it, as shown on the left of Figure 3-22. Next, click the down arrow key on the directional pad. Observe the message shown on the screen, as shown in the black area on the right of Figure 3-22. Figure 3-22 How It Works When the activity is loaded, the cursor will be blinking in the EditText view, as it has the focus.
- 139. Listening for UI Notifications ❘ 117 In the MainActivitiy class, you override the onKeyDown() method of the base Activity class, like this: @Override public boolean onKeyDown(int keyCode, KeyEvent event) { switch (keyCode) { case KeyEvent.KEYCODE_DPAD_CENTER: //... break; case KeyEvent.KEYCODE_DPAD_LEFT: //... break; case KeyEvent.KEYCODE_DPAD_RIGHT: //... break; case KeyEvent.KEYCODE_DPAD_UP: //... break; case KeyEvent.KEYCODE_DPAD_DOWN: //... break; } return false; } In Android, whenever you press any keys on your device, the view that currently has the focus will try to handle the event generated. In this case, when the EditText has the focus and you press a key, the EditText view will handle the event and display the character you have just pressed in the view. However, if you press the up or down directional arrow key, the EditText view does not handle this, and instead passes the event to the activity. In this case, the onKeyDown() method is called. In this case, you checked the key that was pressed and displayed a message indicating the key pressed. Observe that the focus is now also transferred to the next view, which is the OK button. Interestingly, if the EditText view already has some text in it and the cursor is at the end of the text (see Figure 3-23), then clicking the left arrow key does not fire the onKeyDown() event; it simply moves the cursor one character to the left. This is because the EditText view has already handled the event. If you press the right arrow key instead, then the onKeyDown() method will be called (because now the EditText view will not be handling the event). The same applies when the cursor is at the beginning of the EditText view. Clicking the left arrow will fire the onKeyDown() event, whereas clicking the Figure 3-23 right arrow will simply move the cursor one character to the right. With the OK button in focus, press the center button in the directional pad. Observe that the message “Center was clicked” is not displayed. This is because the Button view itself is handling the click event. Hence the event is not caught by the onKeyDown() method. However, if none of the views is in focus at the moment (you can achieve this by clicking on the background of the screen), then pressing the center key will show the “Center was clicked” message (see Figure 3-24).
- 140. 118 ❘ Chapter 3 Getting to Know the Android User Interface Figure 3-24 Note that the onKeyDown() method returns a boolean result. You should return true when you want to tell the system that you are done with the event and that the system should not proceed further with it. For example, consider the case when you return true after each key has been matched: @Override public boolean onKeyDown(int keyCode, KeyEvent event) { switch (keyCode) { case KeyEvent.KEYCODE_DPAD_CENTER: Toast.makeText(getBaseContext(), “Center was clicked”, Toast.LENGTH_LONG).show(); return true; case KeyEvent.KEYCODE_DPAD_LEFT: Toast.makeText(getBaseContext(), “Left arrow was clicked”, Toast.LENGTH_LONG).show(); return true; case KeyEvent.KEYCODE_DPAD_RIGHT: Toast.makeText(getBaseContext(), “Right arrow was clicked”, Toast.LENGTH_LONG).show(); return true; case KeyEvent.KEYCODE_DPAD_UP: Toast.makeText(getBaseContext(), “Up arrow was clicked”, Toast.LENGTH_LONG).show();
- 141. Listening for UI Notifications ❘ 119 return true; case KeyEvent.KEYCODE_DPAD_DOWN: Toast.makeText(getBaseContext(), “Down arrow was clicked”, Toast.LENGTH_LONG).show(); return true; } return false; } If you test this, you will see that now you cannot navigate between the views using the arrow keys. Registering Events for Views Views can fire events when users interact with them. For example, when a user touches a Button view, you need to service the event so that the appropriate action can be performed. To do so, you need to explicitly register events for views. Using the same example discussed in the previous section, recall that the activity has two Button views; therefore, you can register the button click events using an anonymous class as shown here: package net.learn2develop.UIActivity; import android.app.Activity; import android.os.Bundle; import android.view.KeyEvent; import android.view.View; import android.widget.Toast; import android.view.View.OnClickListener; import android.widget.Button; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---the two buttons are wired to the same event handler--- Button btn1 = (Button)findViewById(R.id.btn1); btn1.setOnClickListener(btnListener); Button btn2 = (Button)findViewById(R.id.btn2); btn2.setOnClickListener(btnListener); } //---create an anonymous class to act as a button click listener--- private OnClickListener btnListener = new OnClickListener() { public void onClick(View v)
- 142. 120 ❘ Chapter 3 Getting to Know the Android User Interface { Toast.makeText(getBaseContext(), ((Button) v).getText() + “ was clicked”, Toast.LENGTH_LONG).show(); } }; @Override public boolean onKeyDown(int keyCode, KeyEvent event) { switch (keyCode) { //... //... } return false; } } If you now press either the OK button or the Cancel button, the appropriate message will be dis- played (see Figure 3-25), proving that the event is wired up properly. Figure 3-25 Besides defining an anonymous class for the event handler, you can also define an anonymous inner class to handle an event. The following example shows how you can handle the onFocusChange() event for the EditText view: import android.widget.EditText; public class MainActivity extends Activity {
- 143. Listening for UI Notifications ❘ 121 /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---the two buttons are wired to the same event handler--- Button btn1 = (Button)findViewById(R.id.btn1); btn1.setOnClickListener(btnListener); Button btn2 = (Button)findViewById(R.id.btn2); btn2.setOnClickListener(btnListener); EditText txt1 = (EditText)findViewById(R.id.txt1); //---create an anonymous inner class to act as an onfocus listener--- txt1.setOnFocusChangeListener(new View.OnFocusChangeListener() { @Override public void onFocusChange(View v, boolean hasFocus) { Toast.makeText(getBaseContext(), ((EditText) v).getId() + “ has focus - “ + hasFocus, Toast.LENGTH_LONG).show(); } }); } As shown in Figure 3-26, when the EditText view receives the focus, a message is printed on the screen. Figure 3-26
- 144. 122 ❘ Chapter 3 Getting to Know the Android User Interface Summary In this chapter, you have learned how user interfaces are created in Android. You have also learned about the different layouts that you can use to position the views in your Android UI. Because Android devices support more than one screen orientation, you need to take special care to ensure that your UI can adapt to changes in screen orientation. Exercises 1 . What is the difference between the dp unit and the px unit? Which one should you use to specify the dimension of a view? 2 . Why is the AbsoluteLayout not recommended for use? . 3 What is the difference between the onPause()event and the onSaveInstanceState() event? 4. Name the three events you can override to save an activity’s state. Answers to Exercises can be found in Appendix C.
- 145. Summary ❘ 123 ⊲⊲ What You Learned In This Chapter Topic Key Concepts LinearLayout Arranges views in a single column or single row AbsoluteLayout Enables you to specify the exact location of its children TableLayout Groups views into rows and columns RelativeLayout Enables you to specify how child views are positioned relative to each other FrameLayout A placeholder on screen that you can use to display a single view ScrollView A special type of FrameLayout in that it enables users to scroll through a list of views that occupy more space than the physical display allows Unit of Measure Use the dp for specifying the dimension of views and sp for font size Two ways to adapt Anchoring, and resizing and repositioning to changes in orientation Using different Use the layout folder for portrait UI, and layout-land for landscape UI. XML files for dif- ferent orientations Three ways to per- Use the onPause() event. sist activity state Use the onSaveInstanceState() event. Use the onRetainNonConfigurationInstance() event. Getting the dimen- Use the WindowManager class’s getDefaultDisplay() method. sion of the current device Constraining Use the setRequestOrientation() method, or the the activity’s android:screenOrientation attribute in the AndroidManifest.xml file. orientation
- 147. 4 Designing Your User interface Using Views WhAt you Will leArn in thiS chApter ➤➤ How to use the basic views in Android to design your user interface ➤➤ How to use the picker views to display lists of items ➤➤ How to use the list views to display lists of items In the previous chapter, you learned about the various layouts that you can use to position your views in an activity. You also learned about the techniques you can use to adapt to differ- ent screen resolutions and sizes. In this chapter, you will take a look at the various views that you can use to design the user interface for your applications. In particular, you will learn about the following view groups: ➤➤ Basic views — Commonly used views such as the TextView, EditText, and Button views ➤➤ Picker views — Views that enable users to select from a list, such as the TimePicker and DatePicker views ➤➤ List views — Views that display a long list of items, such as the ListView and the SpinnerView views Subsequent chapters will cover the other views not covered in this chapter, such as the date and time picker views and other views for displaying graphics, etc.
- 148. 126 ❘ chApter 4 deSiGninG YoUr USer interface USinG viewS BASic vieWS To get started, let’s explore some of the basic views that you can use to design the UI of your Android applications: ➤➤ TextView ➤➤ EditText ➤➤ Button ➤➤ ImageButton ➤➤ CheckBox ➤➤ ToggleButton ➤➤ RadioButton ➤➤ RadioGroup These basic views enable you to display text information, as well as perform some basic selection. The following sections explore all these views in more detail. textview view When you create a new Android project, Eclipse always creates the main.xml fi le (located in the res/ layout folder), which contains a <TextView> element: <?xmlversion=”1.0”encoding=”utf-8”?> <LinearLayoutxmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”@string/hello” /> </LinearLayout> The TextView view is used to display text to the user. This is the most basic view and one that you will frequently use when you develop Android applications. If you need to allow users to edit the text displayed, you should use the subclass of TextView, EditText, which is discussed in the next section. NOTE In some other platforms, the TextView is commonly known as the label view. Its sole purpose is to display text on the screen.
- 149. Basic Views ❘ 127 Button, imageButton, edittext, checkBox, toggleButton, radioButton, and radiogroup views Besides the TextView view, which you will likely use the most often, there are some other basic controls that you will find yourself frequently using: Button, ImageButton, EditText, CheckBox, ToggleButton, RadioButton, and RadioGroup: ➤➤ Button — Represents a push-button widget ➤➤ ImageButton — Similar to the Button view, except that it also displays an image ➤➤ EditText — A subclass of the TextView view, except that it allows users to edit its text content ➤➤ CheckBox — A special type of button that has two states: checked or unchecked ➤➤ RadioGroup and RadioButton — The RadioButton has two states: either checked or unchecked. Once a RadioButton is checked, it cannot be unchecked. A RadioGroup is used to group together one or more RadioButton views, thereby allowing only one RadioButton to be checked within the RadioGroup. ➤➤ ToggleButton — Displays checked/unchecked states using a light indicator The following Try It Out provides details about how these views work. try it out Using the Basic Views codefile BasicViews1.zip available for download at Wrox.com 1 . Using Eclipse, create an Android project and name it as shown in Figure 4-1. NOTE For subsequent projects that you will create in this book, the various fields for the project will adopt the following values: ➤➤ Application Name: <project name> ➤➤ Package name: net.learn2develop.<project name> ➤➤ Create Activity: MainActivity ➤➤ Min SDK Version: 9 2 . Modify the main.xml file located in the res/layout folder by adding the following elements shown in bold: <?xmlversion=”1.0”encoding=”utf-8”?> <LinearLayoutxmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent”
- 150. 128 ❘ Chapter 4 Designing Your User Interface Using Views android:layout_height=”fill_parent”> <Button android:id=”@+id/btnSave” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Save” /> <Button android:id=”@+id/btnOpen” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Open” /> <ImageButton android:id=”@+id/btnImg1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:src=”@drawable/icon” /> <EditText android:id=”@+id/txtName” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <CheckBox android:id=”@+id/chkAutosave” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Autosave” /> <CheckBox android:id=”@+id/star” style=”?android:attr/starStyle” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> <RadioGroup android:id=”@+id/rdbGp1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:orientation=”vertical” > <RadioButton android:id=”@+id/rdb1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Option 1” /> <RadioButton android:id=”@+id/rdb2” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Option 2” /> </RadioGroup> <ToggleButton android:id=”@+id/toggle1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> </LinearLayout> 3 . To see the views in action, debug the project in Eclipse by selecting the project name and pressing F11. Figure 4-2 shows the various views displayed in the Android Emulator.
- 151. Basic Views ❘ 129 Figure 4-1 Figure 4-2
- 152. 130 ❘ Chapter 4 Designing Your User Interface Using Views 4 . Click on the various views and note how they vary in their look and feel. Figure 4-3 shows the fol- lowing changes to the view: ➤➤ The first CheckBox view (Autosave) is checked. ➤➤ The second CheckBox View (star) is checked. ➤➤ The second RadioButton (Option 2) is selected. ➤➤ The ToggleButton is turned on. Figure 4-3 How It Works So far, all the views are relatively straightforward — they are listed using the <LinearLayout> element, so they are stacked on top of each other when they are displayed in the activity. For the first Button, the layout_width attribute is set to fill_parent so that its width occupies the entire width of the screen: <Button android:id=”@+id/btnSave” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Save” /> For the second Button, the layout_width attribute is set to wrap_content so that its width will be the width of its content — specifically, the text that it is displaying (i.e.,“Open”): <Button android:id=”@+id/btnOpen” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Open” />
- 153. Basic Views ❘ 131 The ImageButton displays a button with an image. The image is set through the src attribute. In this case, you simply use the image used for the application icon: <ImageButton android:id=”@+id/btnImg1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:src=”@drawable/icon” /> The EditText view displays a rectangular region where the user can enter some text. You set the layout _height to wrap_content so that if the user enters a long string of text, its height will automatically be adjusted to fit the content (see Figure 4-4). <EditText android:id=”@+id/txtName” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> Figure 4-4 The CheckBox displays a checkbox that users can tap to check or uncheck it: <CheckBox android:id=”@+id/chkAutosave” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Autosave” /> If you do not like the default look of the CheckBox, you can apply a style attribute to it to display it as some other image, such as a star: <CheckBox android:id=”@+id/star” style=”?android:attr/starStyle” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> The format for the value of the style attribute is as follows: ?[package:][type:]name. The RadioGroup encloses two RadioButtons. This is important because radio buttons are usually used to present multiple options to the user for selection. When a RadioButton in a RadioGroup is selected, all other RadioButtons are automatically unselected: <RadioGroup android:id=”@+id/rdbGp1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:orientation=”vertical” > <RadioButton android:id=”@+id/rdb1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Option 1” />
- 154. 132 ❘ Chapter 4 Designing Your User Interface Using Views <RadioButton android:id=”@+id/rdb2” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Option 2” /> </RadioGroup> Notice that the RadioButtons are listed vertically, one on top of another. If you want to list them hori- zontally, you need to change the orientation attribute to horizontal. You would also need to ensure that the layout_width attribute of the RadioButtons are set to wrap_content: <RadioGroup android:id=”@+id/rdbGp1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:orientation=”horizontal” > <RadioButton android:id=”@+id/rdb1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Option 1” /> <RadioButton android:id=”@+id/rdb2” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”Option 2” /> </RadioGroup> Figure 4-5 shows the RadioButtons displayed horizontally. Figure 4-5 The ToogleButton displays a rectangular button that users can toggle on and off by clicking it: <ToggleButton android:id=”@+id/toggle1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> One thing that has been consistent throughout this example is that each view has the id attribute set to a particular value, such as in the case of the Button: <Button android:id=”@+id/btnSave” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Save” /> The id attribute is an identifier for a view so that it may later be retrieved using the View.findViewById() or Activity.findViewById() methods.
- 155. Basic Views ❘ 133 Now that you have seen how the various views look for an activity, the following Try It Out demon- strates how you can programmatically control them Try It Out Handling View Events 1 . Using the same project created in the previous Try It Out, modify the MainActivity.java file by adding the following statements in bold: package net.learn2develop.BasicViews1; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.CheckBox; import android.widget.RadioButton; import android.widget.RadioGroup; import android.widget.Toast; import android.widget.ToggleButton; import android.widget.RadioGroup.OnCheckedChangeListener; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---Button view--- Button btnOpen = (Button) findViewById(R.id.btnOpen); btnOpen.setOnClickListener(new View.OnClickListener() { Do public void onClick(View v) { DisplayToast(“You have clicked the Open button”); } }); //---Button view--- Button btnSave = (Button) findViewById(R.id.btnSave); btnSave.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { DisplayToast(“You have clicked the Save button”); } }); //---CheckBox--- CheckBox checkBox = (CheckBox) findViewById(R.id.chkAutosave); checkBox.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { if (((CheckBox)v).isChecked()) DisplayToast(“CheckBox is checked”); else
- 156. 134 ❘ Chapter 4 Designing Your User Interface Using Views DisplayToast(“CheckBox is unchecked”); } }); //---RadioButton--- RadioGroup radioGroup = (RadioGroup) findViewById(R.id.rdbGp1); radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() { public void onCheckedChanged(RadioGroup group, int checkedId) { RadioButton rb1 = (RadioButton) findViewById(R.id.rdb1); if (rb1.isChecked()) { DisplayToast(“Option 1 checked!”); } else { DisplayToast(“Option 2 checked!”); } } }); //---ToggleButton--- ToggleButton toggleButton = (ToggleButton) findViewById(R.id.toggle1); toggleButton.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { if (((ToggleButton)v).isChecked()) DisplayToast(“Toggle button is On”); else DisplayToast(“Toggle button is Off”); } }); } private void DisplayToast(String msg) { Toast.makeText(getBaseContext(), msg, Toast.LENGTH_SHORT).show(); } } 2 . Press F11 to debug the project on the Android Emulator. 3. Click on the various views and observe the message displayed in the Toast window. How It Works To handle the events fired by each view, you first have to programmatically locate the view that you cre- ated during the onCreate() event. You do so using the Activity.findViewById() method, supplying it with the ID of the view: //---Button view--- Button btnOpen = (Button) findViewById(R.id.btnOpen); The setOnClickListener() method registers a callback to be invoked later when the view is clicked: btnOpen.setOnClickListener(new View.OnClickListener() {
- 157. Basic Views ❘ 135 public void onClick(View v) { DisplayToast(“You have clicked the Open button”); } }); The onClick() method is called when the view is clicked. For the CheckBox, to determine its state you have to typecast the argument of the onClick() method to a CheckBox and then check its isChecked() method to see if it is checked: //---CheckBox--- CheckBox checkBox = (CheckBox) findViewById(R.id.chkAutosave); checkBox.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { if (((CheckBox)v).isChecked()) DisplayToast(“CheckBox is checked”); else DisplayToast(“CheckBox is unchecked”); } }); For RadioButton, you need to use the setOnCheckedChangeListener() method on the RadioGroup to register a callback to be invoked when the checked RadioButton changes in this group: //---RadioButton--- RadioGroup radioGroup = (RadioGroup) findViewById(R.id.rdbGp1); radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() { public void onCheckedChanged(RadioGroup group, int checkedId) { RadioButton rb1 = (RadioButton) findViewById(R.id.rdb1); if (rb1.isChecked()) { DisplayToast(“Option 1 checked!”); } else { DisplayToast(“Option 2 checked!”); } } }); When a RadioButton is selected, the onCheckedChanged() method is fired. Within it, you locate individ- ual RadioButtons and then call their isChecked() method to determine which RadioButton is selected. Alternatively, the onCheckedChanged() method contains a second argument that contains a unique iden- tifier of the RadioButton selected. ProgressBar View The ProgressBar view provides visual feedback of some ongoing tasks, such as when you are per- forming a task in the background. For example, you might be downloading some data from the Web and need to update the user about the status of the download. In this case, the ProgressBar view is a good choice for this task.
- 158. 136 ❘ Chapter 4 Designing Your User Interface Using Views Try It Out Using the ProgressBar View codefile BasicViews2.zip available for download at Wrox.com 1 . Using Eclipse, create an Android project and name it as BasicViews2. 2 . Modify the main.xml file located in the res/layout folder by adding the following code in bold: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <ProgressBar android:id=”@+id/progressbar” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> </LinearLayout> 3 . In the MainActivity.java file, add the following statements in bold: package net.learn2develop.BasicViews2; import android.app.Activity; import android.os.Bundle; import android.os.Handler; import android.widget.ProgressBar; public class MainActivity extends Activity { private static int progress; private ProgressBar progressBar; private int progressStatus = 0; private Handler handler = new Handler(); /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); progress = 0; progressBar = (ProgressBar) findViewById(R.id.progressbar); //---do some work in background thread--- new Thread(new Runnable() { public void run() { //---do some work here--- while (progressStatus < 10) { progressStatus = doSomeWork();
- 159. Basic Views ❘ 137 } //---hides the progress bar--- handler.post(new Runnable() { public void run() { //---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE--- progressBar.setVisibility(8); } }); } //---do some long lasting work here--- private int doSomeWork() { try { //---simulate doing some work--- Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } return ++progress; } }).start(); } } 4 . Press F11 to debug the project on the Android Emulator. Figure 4-6 shows the ProgressBar animating. After about five seconds, it will disappear. Figure 4-6
- 160. 138 ❘ Chapter 4 Designing Your User Interface Using Views How It Works The default mode of the ProgressBar view is indeterminate — that is, it shows a cyclic animation. This mode is useful for tasks that do not have a clear indication of when they will be completed, such as when you are sending some data to a web service and waiting for the server to respond. If you simply put the <ProgressBar> element in your main.xml file, it will display a spinning icon continuously. It is your responsibility to stop it when your background task has completed. The code that you have added in the Java file shows how you can spin off a background thread to simu- late performing some long-running tasks. To do so, you use the Thread class together with a Runnable object. The run() method starts the execution of the thread, which in this case calls the doSomeWork() method to simulate doing some work. When the simulated work is done (after about five seconds), you use a Handler object to send a message to the thread to dismiss the ProgressBar: //---do some work in background thread--- new Thread(new Runnable() { public void run() { //---do some work here--- while (progressStatus < 10) { progressStatus = doSomeWork(); } //---hides the progress bar--- handler.post(new Runnable() { public void run() { //---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE--- progressBar.setVisibility(8); } }); } //---do some long lasting work here--- private int doSomeWork() { try { //---simulate doing some work--- Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } return ++progress; } }).start(); When the task is completed, you hide the ProgressBar by setting its Visibility property to GONE (value 8). The difference between the INVISIBLE and GONE constants is that the INVISIBLE constant simply hides the ProgressBar (the region occupied by the ProgressBar is still taking up space in the activity). The GONE con- stant removes the ProgressBar view from the activity and does not take up any space on it.
- 161. Basic Views ❘ 139 The next Try It Out shows how you can change the look of the ProgressBar. Try It Out Customizing the ProgressBar View 1 . Using the same project created in the previous Try It Out, modify the main.xml file as shown here: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <ProgressBar android:id=”@+id/progressbar” android:layout_width=”wrap_content” android:layout_height=”wrap_content” style=”?android:attr/progressBarStyleHorizontal” /> </LinearLayout> 2 . Modify the MainActivity.java file by adding the following statements in bold: /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); progress = 0; progressBar = (ProgressBar) findViewById(R.id.progressbar); progressBar.setMax(200); //---do some work in background thread--- new Thread(new Runnable() { public void run() { //---do some work here--- while (progressStatus < 100) { progressStatus = doSomeWork(); //---Update the progress bar--- handler.post(new Runnable() { public void run() { progressBar.setProgress(progressStatus); } }); } //---hides the progress bar--- handler.post(new Runnable() { public void run()
- 162. 140 ❘ Chapter 4 Designing Your User Interface Using Views { //---0 - VISIBLE; 4 - INVISIBLE; 8 - GONE--- progressBar.setVisibility(8); } }); } //---do some long lasting work here--- private int doSomeWork() { try { //---simulate doing some work--- Thread.sleep(50); } catch (InterruptedException e) { e.printStackTrace(); } return ++progress; } }).start(); } 3 . Press F11 to debug the project on the Android Emulator. 4. Figure 4-7 shows the ProgressBar displaying the progress. The ProgressBar disappears when the progress reaches 50%. Figure 4-7
- 163. Basic Views ❘ 141 How It Works To make the ProgressBar display horizontally, simply set its style attribute to ?android:attr/progress BarStyleHorizontal: <ProgressBar android:id=”@+id/progressbar” android:layout_width=”wrap_content” android:layout_height=”wrap_content” style=”?android:attr/progressBarStyleHorizontal” /> To display the progress, call its setProgress() method, passing in an integer indicating its progress: //---Update the progress bar--- handler.post(new Runnable() { public void run() { progressBar.setProgress(progressStatus); } }); In this example, you set the range of the ProgressBar from 0 to 200 (via the setMax() method). Hence, the ProgressBar will stop and then disappear when it is halfway through (since you only continue to call the doSomeWork() method as long as the progressStatus is less than 100). To ensure that the ProgressBar disappears only when the progress reaches 100%, either set the maximum value to 100, or modify the while loop to stop when the progressStatus reaches 200, like this: //---do some work here--- while (progressStatus < 200) AutoCompleteTextView View The AutoCompleteTextView is a view that is similar to EditText (in fact it is a subclass of EditText), except that it shows a list of completion suggestions automatically while the user is typing. The fol- lowing Try It Out shows how to use the AutoCompleteTextView to automatically help users complete the text entry. Try It Out Using the AutoCompleteTextView codefile BasicViews3.zip available for download at Wrox.com 1 . Using Eclipse, create an Android project and name it BasicViews3. 2 . Modify the main.xml file located in the res/layout folder as shown here in bold: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent”
- 164. 142 ❘ Chapter 4 Designing Your User Interface Using Views android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Name of President” /> <AutoCompleteTextView android:id=”@+id/txtCountries” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> </LinearLayout> 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.BasicViews3; import android.app.Activity; import android.os.Bundle; import android.widget.ArrayAdapter; import android.widget.AutoCompleteTextView; public class MainActivity extends Activity { String[] presidents = { “Dwight D. Eisenhower”, “John F. Kennedy”, “Lyndon B. Johnson”, “Richard Nixon”, “Gerald Ford”, “Jimmy Carter”, “Ronald Reagan”, “George H. W. Bush”, “Bill Clinton”, “George W. Bush”, “Barack Obama” }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, presidents); AutoCompleteTextView textView = (AutoCompleteTextView) findViewById(R.id.txtCountries); textView.setThreshold(3); textView.setAdapter(adapter); } }
- 165. Basic Views ❘ 143 4 . Press F11 to debug the application on the Android Emulator. As shown in Figure 4-8, a list of matching names appears as you type into the AutoCompleteTextView. Figure 4-8 How It Works In the MainActivity class, you first create a String array containing a list of presidents’ names: String[] presidents = { “Dwight D. Eisenhower”, “John F. Kennedy”, “Lyndon B. Johnson”, “Richard Nixon”, “Gerald Ford”, “Jimmy Carter”, “Ronald Reagan”, “George H. W. Bush”, “Bill Clinton”, “George W. Bush”, “Barack Obama” }; The ArrayAdapter object manages the array of strings that will be displayed by the AutoCompleteTextView. In the preceding example, you set the AutoCompleteTextView to display in the simple_dropdown_item_ 1line mode: ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, presidents);
- 166. 144 ❘ Chapter 4 Designing Your User Interface Using Views The setThreshold() method sets the minimum number of characters the user must type before the sug- gestions appear as a drop-down menu: textView.setThreshold(3); The list of suggestions to display for the AutoCompleteTextView is obtained from the ArrayAdapter object: textView.setAdapter(adapter); Picker Views Selecting the date and time is one of the common tasks you need to perform in a mobile application. Android supports this functionality through the TimePicker and DatePicker views. The following sections show how to make use of these views in your activity. TimePicker View The TimePicker view enables users to select a time of the day, in either 24-hour mode or AM/PM mode. The following Try It Out shows you how to use it. Try It Out Using the TimePicker Wiew codefile BasicViews4.zip available for download at Wrox.com 1 . Using Eclipse, create an Android project and name it BasicViews4. 2 . Modify the main.xml file located in the res/layout folder by adding the following lines in bold: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TimePicker android:id=”@+id/timePicker” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> <Button android:id=”@+id/btnSet” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”I am all set!” /> </LinearLayout> 3 . Press F11 to debug the application on the Android Emulator. Figure 4-9 shows the TimePicker in action. Besides clicking on the plus (+) and minus (-) buttons, you can use the numeric keypad on the device to change the hour and minute, and click the AM button to toggle between AM and PM.
- 167. Picker Views ❘ 145 Figure 4-9 4 . Back in Eclipse, add the following statements in bold to the MainActivity.java file: package net.learn2develop.BasicViews4; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.TimePicker; import android.widget.Toast; public class MainActivity extends Activity { TimePicker timePicker; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); timePicker = (TimePicker) findViewById(R.id.timePicker); timePicker.setIs24HourView(true); //---Button view--- Button btnOpen = (Button) findViewById(R.id.btnSet); btnOpen.setOnClickListener(new View.OnClickListener() {
- 168. 146 ❘ Chapter 4 Designing Your User Interface Using Views public void onClick(View v) { Toast.makeText(getBaseContext(), “Time selected:” + timePicker.getCurrentHour() + “:” + timePicker.getCurrentMinute(), Toast.LENGTH_SHORT).show(); } }); } } 5 . Press F11 to debug the application on the Android Emulator. This time, the TimePicker will be displayed in the 24-hour format. Clicking the Button will display the time that you have set in the TimePicker (see Figure 4-10). Figure 4-10 How It Works The TimePicker displays a standard UI to enable users to set a time. By default, it displays the time in the AM/PM format. If you wish to display the time in the 24-hour format, you can use the setIs24Houriew() method. V To programmatically get the time set by the user, use the getCurrentHour() and getCurrentMinute() methods: Toast.makeText(getBaseContext(), “Time selected:” + timePicker.getCurrentHour() + “:” + timePicker.getCurrentMinute(), Toast.LENGTH_SHORT).show();
- 169. Picker Views ❘ 147 NOTE The getCurrentHour() method always returns the hour in 24-hour format, i.e., a value from 0 to 23. Displaying the TimePicker in a Dialog Window While you can display the TimePicker in an activity, a better way is to display it in a dialog window, so that once the time is set, it disappears and doesn’t take up any space in an activity. The following Try It Out shows how to do just that. try it out Using a Dialog to Display the TimePicker View 1 . Using the same project created in the previous Try It Out, modify the MainActivity.java file as shown here: packagenet.learn2develop.BasicViews4; importandroid.app.Activity; importandroid.os.Bundle; importandroid.view.View; importandroid.widget.Button; importandroid.widget.TimePicker; importandroid.widget.Toast; import android.app.Dialog; import android.app.TimePickerDialog; publicclassMainActivityextendsActivity{ TimePickertimePicker; int hour, minute; static final int TIME_DIALOG_ID = 0; /**Calledwhentheactivityisfirstcreated.*/ @Override publicvoidonCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.main); showDialog(TIME_DIALOG_ID); timePicker=(TimePicker)findViewById(R.id.timePicker); timePicker.setIs24HourView(true); //---Buttonview--- ButtonbtnOpen=(Button)findViewById(R.id.btnSet); btnOpen.setOnClickListener(newView.OnClickListener(){ publicvoidonClick(Viewv){ Toast.makeText(getBaseContext(), “Timeselected:”+ timePicker.getCurrentHour().toString()+
- 170. 148 ❘ Chapter 4 Designing Your User Interface Using Views “:” + timePicker.getCurrentMinute().toString(), Toast.LENGTH_SHORT).show(); } }); } @Override protected Dialog onCreateDialog(int id) { switch (id) { case TIME_DIALOG_ID: return new TimePickerDialog( this, mTimeSetListener, hour, minute, false); } return null; } private TimePickerDialog.OnTimeSetListener mTimeSetListener = new TimePickerDialog.OnTimeSetListener() { public void onTimeSet( TimePicker view, int hourOfDay, int minuteOfHour) { hour = hourOfDay; minute = minuteOfHour; Toast.makeText(getBaseContext(), “You have selected : “ + hour + “:” + minute, Toast.LENGTH_SHORT).show(); } }; } 2 . Press F11 to debug the application on the Android Emulator. When the activity is loaded, you can see the TimePicker displayed in a dialog window (see Figure 4-11). Set a time and then click the Set button. You will see the Toast window displaying the time that you just set. How It Works To display a dialog window, you use the showDialog() method, passing it an ID to identify the source of the dialog: showDialog(TIME_DIALOG_ID); When the showDialog() method is called, the onCreateDialog() method will be called: @Override protected Dialog onCreateDialog(int id) { switch (id) { case TIME_DIALOG_ID: return new TimePickerDialog( this, mTimeSetListener, hour, minute, false); } return null; }
- 171. Picker Views ❘ 149 Figure 4-11 Here, you create a new instance of the TimePickerDialog class, passing it the current context, the callback, the initial hour and minute, as well as whether the TimePicker should be displayed in 24-hour format. When the user clicks the Set button in the TimePicker dialog window, the onTimeSet() method will be called: private TimePickerDialog.OnTimeSetListener mTimeSetListener = new TimePickerDialog.OnTimeSetListener() { public void onTimeSet( TimePicker view, int hourOfDay, int minuteOfHour) { hour = hourOfDay; minute = minuteOfHour; Toast.makeText(getBaseContext(), “You have selected : “ + hour + “:” + minute, Toast.LENGTH_SHORT).show(); } }; Here, the onTimeSet() method will contain the hour and minute set by the user via the hourOfDay and minuteOfHour arguments, respectively. DatePicker View Another view that is similar to the TimePicker is the DatePicker. Using the DatePicker, you can enable users to select a particular date on the activity. The following Try It Out shows you how to use the DatePicker.
- 172. 150 ❘ Chapter 4 Designing Your User Interface Using Views Try It Out Using the DatePicker View 1 . Using the same project created in the previous Try It Out, modify the main.xml file as shown here: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <DatePicker android:id=”@+id/datePicker” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> <TimePicker android:id=”@+id/timePicker” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> <Button android:id=”@+id/btnSet” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:text=”I am all set!” /> </LinearLayout> 2 . Press F11 to debug the application on the Android Emulator. Figure 4-12 shows the DatePicker and TimePicker views. Figure 4-12
- 173. Picker Views ❘ 151 3 . Back in Eclipse, add in the following statements in bold to the MainActivity.java file: package net.learn2develop.BasicViews4; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.Toast; import android.app.Dialog; import android.app.TimePickerDialog; import android.widget.TimePicker; import android.widget.DatePicker; public class MainActivity extends Activity { TimePicker timePicker; DatePicker datePicker; int hour, minute; static final int TIME_DIALOG_ID = 0; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //showDialog(TIME_DIALOG_ID); timePicker = (TimePicker) findViewById(R.id.timePicker); timePicker.setIs24HourView(true); datePicker = (DatePicker) findViewById(R.id.datePicker); //---Button view--- Button btnOpen = (Button) findViewById(R.id.btnSet); btnOpen.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { Toast.makeText(getBaseContext(), “Date selected:” + datePicker.getMonth() + 1 + “/” + datePicker.getDayOfMonth() + “/” + datePicker.getYear() + “n” + “Time selected:” + timePicker.getCurrentHour() + “:” + timePicker.getCurrentMinute(), Toast.LENGTH_SHORT).show(); } }); } @Override
- 174. 152 ❘ Chapter 4 Designing Your User Interface Using Views protected Dialog onCreateDialog(int id) { switch (id) { case TIME_DIALOG_ID: return new TimePickerDialog( this, mTimeSetListener, hour, minute, false); } return null; } private TimePickerDialog.OnTimeSetListener mTimeSetListener = new TimePickerDialog.OnTimeSetListener() { public void onTimeSet( TimePicker view, int hourOfDay, int minuteOfHour) { hour = hourOfDay; minute = minuteOfHour; Toast.makeText(getBaseContext(), “You have selected : “ + hour + “:” + minute, Toast.LENGTH_SHORT).show(); } }; } 4 . Press F11 to debug the application on the Android Emulator. Once the date is set, clicking the Button will display the date set (see Figure 4-13). Do Figure 4-13
- 175. Picker Views ❘ 153 How It Works Like the TimePicker, you call the getMonth(), getDayOfMonth(), and getYear() methods to get the month, day, and year, respectively: “Date selected:” + datePicker.getMonth() + 1 + “/” + datePicker.getDayOfMonth() + “/” + datePicker.getYear() + “n” + Note that the getMonth()method returns 0 for January, 1 for February, and so on. Hence, you need to add a one to the result of this method to get the month number. Displaying the DatePicker View in a Dialog Window Like the TimePicker, you can also display the DatePicker in a dialog window. The following Try It Out shows you how. Try It Out Using a Dialog to Display the DatePicker View 1 . Using the same project created in the previous Try It Out, add the following statements in bold to the MainActivity.java file: package net.learn2develop.BasicViews4; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.Toast; import android.app.Dialog; import android.app.TimePickerDialog; import android.widget.TimePicker; import android.widget.DatePicker; import android.app.DatePickerDialog; import java.util.Calendar; public class MainActivity extends Activity { TimePicker timePicker; DatePicker datePicker; int hour, minute; int yr, month, day; static final int TIME_DIALOG_ID = 0; static final int DATE_DIALOG_ID = 1; /** Called when the activity is first created. */
- 176. 154 ❘ Chapter 4 Designing Your User Interface Using Views @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //showDialog(TIME_DIALOG_ID); //---get the current date--- Calendar today = Calendar.getInstance(); yr = today.get(Calendar.YEAR); month = today.get(Calendar.MONTH); day = today.get(Calendar.DAY_OF_MONTH); showDialog(DATE_DIALOG_ID); timePicker = (TimePicker) findViewById(R.id.timePicker); timePicker.setIs24HourView(true); datePicker = (DatePicker) findViewById(R.id.datePicker); //---Button view--- Button btnOpen = (Button) findViewById(R.id.btnSet); btnOpen.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { Toast.makeText(getBaseContext(), “Date selected:” + datePicker.getMonth() + “/” + datePicker.getDayOfMonth() + “/” + datePicker.getYear() + “n” + “Time selected:” + timePicker.getCurrentHour() + “:” + timePicker.getCurrentMinute(), Toast.LENGTH_SHORT).show(); } }); } @Override protected Dialog onCreateDialog(int id) { switch (id) { case TIME_DIALOG_ID: return new TimePickerDialog( this, mTimeSetListener, hour, minute, false); case DATE_DIALOG_ID: return new DatePickerDialog( this, mDateSetListener, yr, month, day); } return null; } private DatePickerDialog.OnDateSetListener mDateSetListener = new DatePickerDialog.OnDateSetListener() { public void onDateSet( DatePicker view, int year, int monthOfYear, int dayOfMonth) {
- 177. Picker Views ❘ 155 yr = year; month = monthOfYear; day = dayOfMonth; Toast.makeText(getBaseContext(), “You have selected : “ + (month + 1) + “/” + day + “/” + year, Toast.LENGTH_SHORT).show(); } }; private TimePickerDialog.OnTimeSetListener mTimeSetListener = new TimePickerDialog.OnTimeSetListener() { public void onTimeSet( TimePicker view, int hourOfDay, int minuteOfHour) { hour = hourOfDay; minute = minuteOfHour; Toast.makeText(getBaseContext(), “You have selected : “ + hour + “:” + minute, Toast.LENGTH_SHORT).show(); } }; } 2 . Press F11 to debug the application on the Android Emulator. When the activity is loaded, you can see the DatePicker displayed in a dialog window (see Figure 4-14). Set a date and then click the Set button. The Toast window will display the date you have just set. Figure 4-14
- 178. 156 ❘ Chapter 4 Designing Your User Interface Using Views How It Works The DatePicker works exactly like the TimePicker. When a date is set, it fires the onDateSet() method, where you can obtain the date set by the user: public void onDateSet( DatePicker view, int year, int monthOfYear, int dayOfMonth) { yr = year; month = monthOfYear; day = dayOfMonth; Toast.makeText(getBaseContext(), “You have selected : “ + (month + 1) + “/” + day + “/” + year, Toast.LENGTH_SHORT).show(); } Note that you have to initialize the three variables — yr, month, and day — before showing the dialog: //---get the current date--- Calendar today = Calendar.getInstance(); yr = today.get(Calendar.YEAR); month = today.get(Calendar.MONTH); day = today.get(Calendar.DAY_OF_MONTH); showDialog(DATE_DIALOG_ID); If you don’t, you will get an illegal argument exception error during run time (“current should be >= start and <= end”) when you create an instance of the DatePickerDialog class. List Views List views are views that enable you to display a long list of items. In Android, there are two types of list views: ListView and SpinnerView. Both are useful for displaying long lists of items. The fol- lowing Try It Outs show them in action. ListView View The ListView displays a list of items in a vertically scrolling list. The following Try It Out demon- strates how to display a list of items using the ListView. Try It Out Displaying a Long List of Items Using the ListView 1 . Using Eclipse, create an Android project and name it BasicView5. codefile BasicViews5.zip available for download at Wrox.com
- 179. List Views ❘ 157 2 . Modify the MainActivity.java file by inserting the statements shown here in bold: package net.learn2develop.BasicViews5; import android.app.Activity; import android.os.Bundle; import android.app.ListActivity; import android.view.View; import android.widget.ArrayAdapter; import android.widget.ListView; import android.widget.Toast; public class MainActivity extends ListActivity { String[] presidents = { “Dwight D. Eisenhower”, “John F. Kennedy”, “Lyndon B. Johnson”, “Richard Nixon”, “Gerald Ford”, “Jimmy Carter”, “Ronald Reagan”, “George H. W. Bush”, “Bill Clinton”, “George W. Bush”, “Barack Obama” }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //setContentView(R.layout.main); setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, presidents)); } public void onListItemClick( ListView parent, View v, int position, long id) { Toast.makeText(this, “You have selected “ + presidents[position], Toast.LENGTH_SHORT).show(); } } 3 . Press F11 to debug the application on the Android Emulator. Figure 4-15 shows the activity dis- playing the list of presidents’ names.
- 180. 158 ❘ Chapter 4 Designing Your User Interface Using Views Figure 4-15 4 . Click on an item. A message containing the item selected will be displayed. How It Works The first thing to notice in this example is that the MainActivity class extends the ListActivity class. The ListActivity class extends the Activity class and it displays a list of items by binding to a data source. Also, note that there is no need to modify the main.xml file to include the ListView; the ListActivity class itself contains a ListView. Hence, in the onCreate() method, there is no need to call the setContentiew() method to load the UI from the main.xml file: V //---no need to call this--- //setContentView(R.layout.main); In the onCreate() method, you use the setListAdapter() method to programmatically fill the entire screen of the activity with a ListView. The ArrayAdapter object manages the array of strings that will be displayed by the ListView. In the preceding example, you set the ListView to display in the simple_ list_item_1 mode: setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, presidents)); The onListItemClick() method is fired whenever an item in the ListView has been clicked: public void onListItemClick( ListView parent, View v, int position, long id)
- 181. List Views ❘ 159 { Toast.makeText(this, “You have selected “ + presidents[position], Toast.LENGTH_SHORT).show(); } Here, you simply display the name of the president selected using the Toast class. Customizing the ListView The ListView is a versatile control that you can further customize. The following Try It Out shows how you can allow multiple items in the ListView to be selected and how you can enable filtering support. Try It Out Customizing the ListView 1 . Using the same project created in the previous section, add the following statements in bold to the MainActivity.java file: /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); ListView lstView = getListView(); //lstView.setChoiceMode(0); //CHOICE_MODE_NONE //lstView.setChoiceMode(1); //CHOICE_MODE_SINGLE lstView.setChoiceMode(2); //CHOICE_MODE_MULTIPLE lstView.setTextFilterEnabled(true); setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_checked, presidents)); } public void onListItemClick( ListView parent, View v, int position, long id) { //---toggle the check displayed next to the item--- parent.setItemChecked(position, parent.isItemChecked(position)); Toast.makeText(this, “You have selected “ + presidents[position], Toast.LENGTH_SHORT).show(); } 2 . Press F11 to debug the application on the Android Emulator. You can now click on each item to display the check icon next to it (see Figure 4-16).
- 182. 160 ❘ Chapter 4 Designing Your User Interface Using Views Figure 4-16 How It Works To programmatically get a reference to the ListView object, you use the getListView() method, which fetches the ListActivity’s list view. You need to do this so that you can programmatically modify the behavior of the ListView. In this case, you used the setChoiceMode() method to tell the ListView how it should handle a user’s click. For this example, you set it to 2, which means that the user can select multiple items: //lstView.setChoiceMode(0); //CHOICE_MODE_NONE //lstView.setChoiceMode(1); //CHOICE_MODE_SINGLE lstView.setChoiceMode(2); //CHOICE_MODE_MULTIPLE A very cool feature of the ListView is its support for filtering. When you enable filtering through the setTextFilterEnabled() method, users will be able to type on the keypad and the ListView will auto- matically filter to match what you have typed: lstView.setTextFilterEnabled(true); Figure 4-17 shows the list filtering in action. Here, all items in the list that contain the word “john” will appear in the result list. To display the check icon displayed next to each item, use the setItemChecked() method: //---toggle the check displayed next to the item--- parent.setItemChecked(position, parent.isItemChecked(position)); The preceding statement will toggle the check icon for each item when you click on it.
- 183. List Views ❘ 161 Figure 4-17 While this example shows that the list of presidents’ names is stored in an array, in a real-life appli- cation it is recommended that you either retrieve them from a database or at least store them in the strings.xml file. The following Try It Out shows you how. Try It Out Storing Items in the strings.xml File 1 . Using the same project created in the previous section, add the following lines in bold to the strings.xml file located in the res/values folder: <?xml version=”1.0” encoding=”utf-8”?> <resources> <string name=”hello”>Hello World, MainActivity!</string> <string name=”app_name”>BasicViews5</string> <string-array name=”presidents_array”> <item>Dwight D. Eisenhower</item> <item>John F. Kennedy</item> <item>Lyndon B. Johnson</item> <item>Richard Nixon</item> <item>Gerald Ford</item> <item>Jimmy Carter</item> <item>Ronald Reagan</item> <item>George H. W. Bush</item> <item>Bill Clinton</item> <item>George W. Bush</item> <item>Barack Obama</item> </string-array> </resources>
- 184. 162 ❘ Chapter 4 Designing Your User Interface Using Views 2 . Modify the MainActivity.java file as shown in bold: public class MainActivity extends ListActivity { String[] presidents; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); ListView lstView = getListView(); //lstView.setChoiceMode(0); //CHOICE_MODE_NONE //lstView.setChoiceMode(1); //CHOICE_MODE_SINGLE lstView.setChoiceMode(2); //CHOICE_MODE_MULTIPLE lstView.setTextFilterEnabled(true); presidents = getResources().getStringArray(R.array.presidents_array); setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_checked, presidents)); } public void onListItemClick( ListView parent, View v, int position, long id) { //... //... } }; 3 . Press F11 to debug the application on the Android Emulator. You should see the same list of names that appeared in the previous Try It Out. How It Works With the names now stored in the strings.xml file, you can retrieve it programmatically in this MainActivity.java file using the getResources() method: presidents = getResources().getStringArray(R.array.presidents_array); In general, you can programmatically retrieve resources bundled with your application using the getResources() method. Using the Spinner View The ListView displays a long list of items in an activity, but sometimes you may want your user interface to display other views, and hence you do not have the additional space for a full-screen view
- 185. List Views ❘ 163 like the ListView. In such cases, you should use the SpinnerView. The SpinnerView displays one item at a time from a list and enables users to choose among them. The following Try It Out shows how you can use the SpinnerView in your activity. Try It Out Using the SpinnerView to Display an Item at a Time 1 . Using Eclipse, create an Android project and name it as BasicViews6. codefile BasicViews6.zip available for download at Wrox.com 2 . Modify the main.xml file located in the res/layout folder as shown here: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <Spinner android:id=”@+id/spinner1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:drawSelectorOnTop=”true” /> </LinearLayout> 3 . Add the following lines in bold to the strings.xml file located in the res/values folder: <?xml version=”1.0” encoding=”utf-8”?> <resources> <string name=”hello”>Hello World, MainActivity!</string> <string name=”app_name”>BasicViews6</string> <string-array name=”presidents_array”> <item>Dwight D. Eisenhower</item> <item>John F. Kennedy</item> <item>Lyndon B. Johnson</item> <item>Richard Nixon</item> <item>Gerald Ford</item> <item>Jimmy Carter</item> <item>Ronald Reagan</item> <item>George H. W. Bush</item> <item>Bill Clinton</item> <item>George W. Bush</item> <item>Barack Obama</item> </string-array> </resources> 4 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.BasicViews6; import android.app.Activity;
- 186. 164 ❘ Chapter 4 Designing Your User Interface Using Views import android.os.Bundle; import android.view.View; import android.widget.AdapterView; import android.widget.AdapterView.OnItemSelectedListener; import android.widget.ArrayAdapter; import android.widget.Spinner; import android.widget.Toast; public class MainActivity extends Activity { String[] presidents; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); presidents = getResources().getStringArray(R.array.presidents_array); Spinner s1 = (Spinner) findViewById(R.id.spinner1); ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, presidents); s1.setAdapter(adapter); s1.setOnItemSelectedListener(new OnItemSelectedListener() { @Override public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) { int index = arg0.getSelectedItemPosition(); Toast.makeText(getBaseContext(), “You have selected item : “ + presidents[index], Toast.LENGTH_SHORT).show(); } @Override public void onNothingSelected(AdapterView<?> arg0) {} }); } } 5 . Press F11 to debug the application on the Android Emulator. Click on the SpinnerView and you will see a pop-up displaying the list of presidents’ names (see Figure 4-18). Clicking on an item will display a message showing you the item selected. How It Works The preceding example works very much like the ListView. One additional method you need to implement is the onNothingSelected() method. This method is fired when the user presses the Back button, which dismisses the list of items displayed. In this case, nothing is selected and you do not need to do anything.
- 187. List Views ❘ 165 Figure 4-18 Instead of displaying the items in the ArrayAdapter as a simple list, you can also display them using radio buttons. To do so, modify the second parameter in the constructor of the ArrayAdapter class: ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, presidents); This will cause the items to be displayed as a list of radio buttons (see Figure 4-19). Figure 4-19
- 188. 166 ❘ Chapter 4 Designing Your User Interface Using Views Summary This chapter provided a brief look at some of the commonly used views in an Android application. While it is not possible to exhaustively examine each view in detail, the views you learned about here should provide a good foundation for designing your Android application’s user interface, regardless of its requirements. Exercises 1 . How do you programmatically determine whether a RadioButton is checked? . 2 How do you access the string resource stored in the strings.xml file? . 3 Write the code snippet to obtain the current date. Answers to the Exercises can be found in Appendix C.
- 189. Summary ❘ 167 ⊲⊲ What You Learned In This Chapter Topic Key Concepts TextView <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”@string/hello” /> Button <Button android:id=”@+id/btnSave” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Save” /> ImageButton <ImageButton android:id=”@+id/btnImg1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:src=”@drawable/icon” /> EditText <EditText android:id=”@+id/txtName” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> CheckBox <CheckBox android:id=”@+id/chkAutosave” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Autosave” /> RadioGroup and RadioButton <RadioGroup android:id=”@+id/rdbGp1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:orientation=”vertical” > <RadioButton android:id=”@+id/rdb1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Option 1” /> <RadioButton android:id=”@+id/rdb2” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Option 2” /> </RadioGroup> ToggleButton <ToggleButton android:id=”@+id/toggle1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> ProgressBar <ProgressBar android:id=”@+id/progressbar” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> AutoCompleteTextBox <AutoCompleteTextView android:id=”@+id/txtCountries” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> continues
- 190. 168 ❘ Chapter 4 Designing Your User Interface Using Views (continued) Topic Key Concepts TimePicker <TimePicker android:id=”@+id/timePicker” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> DatePicker <DatePicker android:id=”@+id/datePicker” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> Spinner <Spinner android:id=”@+id/spinner1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:drawSelectorOnTop=”true” />
- 191. 5 Displaying Pictures and Menus with Views WhAt you Will leArn in thiS chApter ➤➤ How to use the Gallery, ImageSwitcher, GridView, and ImageView views to display images ➤➤ How to display options and context menus ➤➤ How to display time using the AnalogClock and DigitalClock views ➤➤ How to display Web content using the WebView In the previous chapter, you learned about the various views that you can use to build the user interface of your Android application. In this chapter, you continue your exploration of the other views that you can use to create robust and compelling applications. In particular, you shall turn your attention to views that enable you to display images. In addition, you will also learn how to create option and context menus in your Android application. This chap- ter ends with a discussion of some nice views that enable you to display the current time and Web content. uSing imAge vieWS to diSplAy pictureS So far, all the views you have seen until this point are used to display text information. For displaying images, you can use the ImageView, Gallery, ImageSwitcher, and GridView views. The following sections discuss each view in more detail.
- 192. 170 ❘ Chapter 5 Displaying Pictures and Menus with Views Gallery and ImageView Views The Gallery is a view that shows items (such as images) in a center-locked, horizontal scrolling list. Figure 5-1 shows how the Gallery view looks when it is displaying some images. Figure 5-1 The following Try It Out shows you how to use the Gallery view to display a set of images. Try It Out Using the Gallery View codefile Gallery.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project as shown in Figure 5-2. Figure 5-2
- 193. Using image Views to Display Pictures ❘ 171 2 . Modify the main.xml file as shown in bold: <?xmlversion=”1.0”encoding=”utf-8”?> <LinearLayoutxmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent”> <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Images of San Francisco” /> <Gallery android:id=”@+id/gallery1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <ImageView android:id=”@+id/image1” android:layout_width=”320px” android:layout_height=”250px” android:scaleType=”fitXY” /> </LinearLayout> 3 . Right-click on the res/values folder and select New ➪ File. Name the file attrs.xml. 4 . Populate the attrs.xml file as follows: <?xml version=”1.0” encoding=”utf-8”?> <resources> <declare-styleable name=”Gallery1”> <attr name=”android:galleryItemBackground” /> </declare-styleable> </resources> 5 . Prepare a series of images and name them pic1.png, pic2.png, and so on for each subsequent image (see Figure 5-3). NOTE You can download the series of images from this book’s support website at www.wrox.com. 6 . Drag and drop all the images into the res/drawable-mdpi folder (see Figure 5-4). When a dialog is displayed, check the copy option and click OK. NOTE This example assumes that this project will be tested on an AVD with medium DPI screen resolution. For a real-life project, you need to ensure that each drawable folder has a set of images (of different resolutions).
- 194. 172 ❘ Chapter 5 Displaying Pictures and Menus with Views Figure 5-3 Figure 5-4 7 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Gallery; import android.app.Activity; import android.os.Bundle; import android.content.Context; import android.content.res.TypedArray; Do import android.view.View; import android.view.ViewGroup; import android.widget.AdapterView; import android.widget.AdapterView.OnItemClickListener; import android.widget.BaseAdapter; import android.widget.Gallery; import android.widget.ImageView; import android.widget.Toast; public class MainActivity extends Activity { //---the images to display--- Integer[] imageIDs = { R.drawable.pic1, R.drawable.pic2, R.drawable.pic3, R.drawable.pic4, R.drawable.pic5, R.drawable.pic6, R.drawable.pic7 }; /** Called when the activity is first created. */ @Override
- 195. Using Image Views to Display Pictures ❘ 173 public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Gallery gallery = (Gallery) findViewById(R.id.gallery1); gallery.setAdapter(new ImageAdapter(this)); gallery.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { Toast.makeText(getBaseContext(), “pic” + (position + 1) + “ selected”, Toast.LENGTH_SHORT).show(); } }); } public class ImageAdapter extends BaseAdapter { private Context context; private int itemBackground; public ImageAdapter(Context c) { context = c; //---setting the style--- TypedArray a = obtainStyledAttributes(R.styleable.Gallery1); itemBackground = a.getResourceId( R.styleable.Gallery1_android_galleryItemBackground, 0); a.recycle(); } //---returns the number of images--- public int getCount() { return imageIDs.length; } //---returns the ID of an item--- public Object getItem(int position) { return position; } //---returns the ID of an item--- public long getItemId(int position) { return position; } //---returns an ImageView view--- public View getView(int position, View convertView, ViewGroup parent) { ImageView imageView = new ImageView(context); imageView.setImageResource(imageIDs[position]); imageView.setScaleType(ImageView.ScaleType.FIT_XY); imageView.setLayoutParams(new Gallery.LayoutParams(150, 120)); imageView.setBackgroundResource(itemBackground);
- 196. 174 ❘ Chapter 5 Displaying Pictures and Menus with Views return imageView; } } } 8 . Press F11 to debug the application on the Android Emulator. Figure 5-5 shows the Gallery view displaying the series of images. 9. You can swipe the images to view the entire series of images. Observe that as you click on an image, the Toast class will display its name (see Figure 5-6). Figure 5-5 Figure 5-6
- 197. Using Image Views to Display Pictures ❘ 175 1 0. To display the selected image in the ImageView, add the following statements in bold to the MainActivity.java file: /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Gallery gallery = (Gallery) findViewById(R.id.gallery1); gallery.setAdapter(new ImageAdapter(this)); gallery.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { Toast.makeText(getBaseContext(), “pic” + (position + 1) + “ selected”, Toast.LENGTH_SHORT).show(); //---display the images selected--- ImageView imageView = (ImageView) findViewById(R.id.image1); imageView.setImageResource(imageIDs[position]); } }); } 1 1. Press F11 to debug the application again. This time, you will see the image selected in the ImageView (see Figure 5-7). Figure 5-7
- 198. 176 ❘ Chapter 5 Displaying Pictures and Menus with Views How It Works You first add the Gallery and ImageView views to main.xml: <Gallery android:id=”@+id/gallery1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <ImageView android:id=”@+id/image1” android:layout_width=”320px” android:layout_height=”250px” android:scaleType=”fitXY” /> As mentioned earlier, the Gallery view is used to display the series of images in a horizontal scrolling list. The ImageView is used to display the image selected by the user. The list of images to be displayed is stored in the imageIDs array: //---the images to display--- Integer[] imageIDs = { R.drawable.pic1, R.drawable.pic2, R.drawable.pic3, R.drawable.pic4, R.drawable.pic5, R.drawable.pic6, R.drawable.pic7 }; You create the ImageAdapter class (which extends the BaseAdapter class) so that it can bind to the Gallery view with a series of ImageView views: Gallery gallery = (Gallery) findViewById(R.id.gallery1); gallery.setAdapter(new ImageAdapter(this)); gallery.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { Toast.makeText(getBaseContext(), “pic” + (position + 1) + “ selected”, Toast.LENGTH_SHORT).show(); //---display the images selected--- ImageView imageView = (ImageView) findViewById(R.id.image1); imageView.setImageResource(imageIDs[position]); } }); When an image in the Gallery view is selected (i.e., clicked), the position (0 for the first image, 1 for the second image, and so on) of the selected image is displayed and the image is displayed in the ImageView.
- 199. Using Image Views to Display Pictures ❘ 177 ImageSwitcher The previous section demonstrated how to use the Gallery view together with an ImageView to dis- play a series of thumbnail images so that when one is selected, the selected image is displayed in the ImageView. However, sometimes you don’t want an image to appear abruptly when the user selects it in the Gallery view — you might, for example, want to apply some animation to the image when it transits from one image to another. In this case, you need to use the ImageSwitcher together with the Gallery view. The following Try It Out shows you how. Try It Out Using the ImageSwitcher View codefile ImageSwitcher.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it as ImageSwitcher. . 2 Modify the main.xml file by adding the following statements in bold: <?xml version=”1.0” encoding=”utf-8”?> <RelativeLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:background=”#ff000000” > <Gallery android:id=”@+id/gallery1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <ImageSwitcher android:id=”@+id/switcher1” android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:layout_alignParentLeft=”true” android:layout_alignParentRight=”true” android:layout_alignParentBottom=”true” /> </RelativeLayout> 3 . Right-click on the res/values folder and select New ➪ File. Name the file attrs.xml. 4. Populate the attrs.xml file as follows: <?xml version=”1.0” encoding=”utf-8”?> <resources> <declare-styleable name=”Gallery1”> <attr name=”android:galleryItemBackground” /> </declare-styleable> </resources> 5 . Drag and drop a series of images into the res/drawable-mdpi folder When a dialog is displayed, check the copy option and click OK.
- 200. 178 ❘ Chapter 5 Displaying Pictures and Menus with Views 6 . Add the following bold statements to the MainActivity.java file: package net.learn2develop.ImageSwitcher; import android.app.Activity; import android.os.Bundle; import android.content.Context; import android.content.res.TypedArray; import android.view.View; import android.view.ViewGroup; import android.view.ViewGroup.LayoutParams; import android.view.animation.AnimationUtils; import android.widget.BaseAdapter; import android.widget.AdapterView; import android.widget.AdapterView.OnItemClickListener; import android.widget.Gallery; import android.widget.ViewSwitcher.ViewFactory; import android.widget.ImageSwitcher; import android.widget.ImageView; public class MainActivity extends Activity implements ViewFactory { //---the images to display--- Integer[] imageIDs = { R.drawable.pic1, R.drawable.pic2, R.drawable.pic3, R.drawable.pic4, R.drawable.pic5, R.drawable.pic6, R.drawable.pic7 }; private ImageSwitcher imageSwitcher; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); imageSwitcher = (ImageSwitcher) findViewById(R.id.switcher1); imageSwitcher.setFactory(this); imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this, android.R.anim.fade_in)); imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this, android.R.anim.fade_out)); Gallery gallery = (Gallery) findViewById(R.id.gallery1); gallery.setAdapter(new ImageAdapter(this)); gallery.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { imageSwitcher.setImageResource(imageIDs[position]);
- 201. Using Image Views to Display Pictures ❘ 179 } }); } public View makeView() { ImageView imageView = new ImageView(this); imageView.setBackgroundColor(0xFF000000); imageView.setScaleType(ImageView.ScaleType.FIT_CENTER); imageView.setLayoutParams(new ImageSwitcher.LayoutParams( LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT)); return imageView; } public class ImageAdapter extends BaseAdapter { private Context context; private int itemBackground; public ImageAdapter(Context c) { context = c; //---setting the style--- TypedArray a = obtainStyledAttributes(R.styleable.Gallery1); itemBackground = a.getResourceId( R.styleable.Gallery1_android_galleryItemBackground, 0); a.recycle(); } //---returns the number of images--- public int getCount() { return imageIDs.length; } //---returns the ID of an item--- public Object getItem(int position) { return position; } public long getItemId(int position) { return position; } //---returns an ImageView view--- public View getView(int position, View convertView, ViewGroup parent) { ImageView imageView = new ImageView(context); imageView.setImageResource(imageIDs[position]);
- 202. 180 ❘ Chapter 5 Displaying Pictures and Menus with Views imageView.setScaleType(ImageView.ScaleType.FIT_XY); imageView.setLayoutParams(new Gallery.LayoutParams(150, 120)); imageView.setBackgroundResource(itemBackground); return imageView; } } } 7 . Press F11 to debug the application on the Android Emulator. Figure 5-8 shows the Gallery and ImageSwitcher views, with both the collection of images as well as the image selected. Figure 5-8 How It Works The first thing you notice in this example is that the MainActivity not only extends Activity, but also implements ViewFactory. To use the ImageSwitcher view, you need to implement the ViewFactory inter- face, which creates the views for use with the ImageSwitcher view. For this, you need to implement the makeView() method: public View makeView() { ImageView imageView = new ImageView(this); imageView.setBackgroundColor(0xFF000000); imageView.setScaleType(ImageView.ScaleType.FIT_CENTER); imageView.setLayoutParams(new ImageSwitcher.LayoutParams( LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT)); return imageView; }
- 203. Using Image Views to Display Pictures ❘ 181 This method creates a new View to be added in the ImageSwitcher view. Like the Gallery example in the previous section, you also implemented an ImageAdapter class so that it can bind to the Gallery view with a series of ImageView views. In the onCreate() method, you get a reference to the ImageSwitcher view and set the animation, specify- ing how images should “fly” in and out of the view. Finally, when an image is selected from the Gallery view, the image is displayed in the ImageSwitcher view: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); imageSwitcher = (ImageSwitcher) findViewById(R.id.switcher1); imageSwitcher.setFactory(this); imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this, android.R.anim.fade_in)); imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this, android.R.anim.fade_out)); Gallery gallery = (Gallery) findViewById(R.id.gallery1); gallery.setAdapter(new ImageAdapter(this)); gallery.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { imageSwitcher.setImageResource(imageIDs[position]); } }); } In this example, when an image is selected in the Gallery view, it will appear by “fading” in. When the next image is selected, the current image will fade out. If you want the image to slide in from the left and slide out to the right when another image is selected, try the following animation: imageSwitcher.setInAnimation(AnimationUtils.loadAnimation(this, android.R.anim.slide_in_left)); imageSwitcher.setOutAnimation(AnimationUtils.loadAnimation(this, android.R.anim.slide_out_right)); Like the previous Try It Out, you also created the ImageAdapter class (which extends the BaseAdapter class) so that it can bind to the Gallery view with a series of ImageView views. GridView The GridView shows items in a two-dimensional scrolling grid. You can use the GridView together with an ImageView to display a series of images. The following Try It Out demonstrates how.
- 204. 182 ❘ Chapter 5 Displaying Pictures and Menus with Views Try It Out Using the GridView View codefile Grid.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it Grid. 2 . Drag and drop a series of images into the res/drawable-mdpi folder (see Figure 5-9). When a dia- log is displayed, check the copy option and click OK. Figure 5-9 3 . Populate the main.xml file with the following content: <?xml version=”1.0” encoding=”utf-8”?> <GridView xmlns:android=”http://schemas.android.com/apk/res/android” android:id=”@+id/gridview” android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:numColumns=”auto_fit” android:verticalSpacing=”10dp” android:horizontalSpacing=”10dp” android:columnWidth=”90dp” android:stretchMode=”columnWidth” android:gravity=”center” /> 4 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Grid; import android.app.Activity; import android.os.Bundle; import android.content.Context; import android.view.View; import android.view.ViewGroup; import android.widget.AdapterView; import android.widget.AdapterView.OnItemClickListener; import android.widget.BaseAdapter; import android.widget.GridView; import android.widget.ImageView; import android.widget.Toast; public class MainActivity extends Activity {
- 205. Using Image Views to Display Pictures ❘ 183 //---the images to display--- Integer[] imageIDs = { R.drawable.pic1, R.drawable.pic2, R.drawable.pic3, R.drawable.pic4, R.drawable.pic5, R.drawable.pic6, R.drawable.pic7 }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); GridView gridView = (GridView) findViewById(R.id.gridview); gridView.setAdapter(new ImageAdapter(this)); gridView.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { Toast.makeText(getBaseContext(), “pic” + (position + 1) + “ selected”, Toast.LENGTH_SHORT).show(); } }); } public class ImageAdapter extends BaseAdapter { private Context context; public ImageAdapter(Context c) { context = c; } //---returns the number of images--- public int getCount() { return imageIDs.length; } //---returns the ID of an item--- public Object getItem(int position) { return position; } //---returns the ID of an item--- public long getItemId(int position) { return position; } //---returns an ImageView view--- public View getView(int position, View convertView,
- 206. 184 ❘ Chapter 5 Displaying Pictures and Menus with Views ViewGroup parent) { ImageView imageView; if (convertView == null) { imageView = new ImageView(context); imageView.setLayoutParams(new GridView.LayoutParams(85, 85)); imageView.setScaleType( ImageView.ScaleType.CENTER_CROP); imageView.setPadding(5, 5, 5, 5); } else { imageView = (ImageView) convertView; } imageView.setImageResource(imageIDs[position]); return imageView; } } } 5 . Press F11 to debug the application on the Android Emulator. Figure 5-10 shows the GridView displaying all the images. Figure 5-10 How It Works Like the Gallery and ImageSwitcher example, you implement the ImageAdapter class and then bind it to the GridView: GridView gridView = (GridView) findViewById(R.id.gridview); gridView.setAdapter(new ImageAdapter(this)); gridView.setOnItemClickListener(new OnItemClickListener()
- 207. Using Menus with Views ❘ 185 { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { Toast.makeText(getBaseContext(), “pic” + (position + 1) + “ selected”, Toast.LENGTH_SHORT).show(); } }); When an image is selected, you display a Toast message indicating the image selected. Within the GridView, you can specify the size of the images and how images are spaced out in the GridView by setting the padding for each image: //---returns an ImageView view--- public View getView(int position, View convertView, ViewGroup parent) { ImageView imageView; if (convertView == null) { imageView = new ImageView(context); imageView.setLayoutParams(new GridView.LayoutParams(85, 85)); imageView.setScaleType( ImageView.ScaleType.CENTER_CROP); imageView.setPadding(5, 5, 5, 5); } else { imageView = (ImageView) convertView; } imageView.setImageResource(imageIDs[position]); return imageView; } Using Menus with Views Menus are useful for displaying additional options that are not directly visible on the main UI of an application. There are two main types of menus in Android: ➤➤ Options menu — Displays information related to the current activity. In Android, you activate the options menu by pressing the MENU key. ➤➤ Context menu — Displays information related to a particular view on an activity. In Android, to activate a context menu you tap and hold on to it. Figure 5-11 shows an example of an options menu in the browser application. The option menu is displayed whenever the user presses the MENU button. The menu items displayed vary according to the current activity that is running. Figure 5-12 shows a context menu that is displayed when the user presses and holds on a hyperlink displayed on the page. The menu items displayed vary according to the component or view currently selected. To activate the context menu, the user selects an item on the screen and either taps and holds it or simply presses the center button on the directional keypad.
- 208. 186 ❘ Chapter 5 Displaying Pictures and Menus with Views Figure 5-11 Figure 5-12 Creating the Helper Methods Before you go ahead and create your options and context menus, you need to create two helper meth- ods. One creates a list of items to show inside a menu, while the other handles the event that is fired when the user selects an item inside the menu. Try It Out Creating the Menu Helper Methods codefile Menus.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it as Menus. 2 . In the MainActivity.java file, add the following statements in bold: package net.learn2develop.Menus; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.widget.Button; import android.widget.Toast; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main);
- 209. Using Menus with Views ❘ 187 } private void CreateMenu(Menu menu) { MenuItem mnu1 = menu.add(0, 0, 0, “Item 1”); { mnu1.setAlphabeticShortcut(‘a’); mnu1.setIcon(R.drawable.icon); } MenuItem mnu2 = menu.add(0, 1, 1, “Item 2”); { mnu2.setAlphabeticShortcut(‘b’); mnu2.setIcon(R.drawable.icon); } MenuItem mnu3 = menu.add(0, 2, 2, “Item 3”); { mnu3.setAlphabeticShortcut(‘c’); mnu3.setIcon(R.drawable.icon); } MenuItem mnu4 = menu.add(0, 3, 3, “Item 4”); { mnu4.setAlphabeticShortcut(‘d’); } menu.add(0, 3, 3, “Item 5”); menu.add(0, 3, 3, “Item 6”); menu.add(0, 3, 3, “Item 7”); } private boolean MenuChoice(MenuItem item) { switch (item.getItemId()) { case 0: Toast.makeText(this, “You clicked on Item 1”, Toast.LENGTH_LONG).show(); return true; case 1: Toast.makeText(this, “You clicked on Item 2”, Toast.LENGTH_LONG).show(); return true; case 2: Toast.makeText(this, “You clicked on Item 3”, Toast.LENGTH_LONG).show(); return true; case 3: Toast.makeText(this, “You clicked on Item 4”, Toast.LENGTH_LONG).show(); return true; case 4: Toast.makeText(this, “You clicked on Item 5”, Toast.LENGTH_LONG).show(); return true; case 5: Toast.makeText(this, “You clicked on Item 6”, Toast.LENGTH_LONG).show(); return true;
- 210. 188 ❘ Chapter 5 Displaying Pictures and Menus with Views case 6: Toast.makeText(this, “You clicked on Item 7”, Toast.LENGTH_LONG).show(); return true; } return false; } } How It Works The preceding example creates two methods: CreateMenu() and MenuChoice(). The CreateMenu() method takes a Menu argument and adds a series of menu items to it. To add a menu item to the menu, you create an instance of the MenuItem class and use the add() method of the Menu object. MenuItem mnu1 = menu.add(0, 0, 0, “Item 1”); { mnu1.setAlphabeticShortcut(‘a’); mnu1.setIcon(R.drawable.icon); } The four arguments of the add() method are as follows: ➤➤ groupId — The group identifier that the menu item should be part of. Use 0 if an item is not in a group. ➤➤ itemId — Unique item ID ➤➤ order — The order in which the item should be displayed ➤➤ title — The text to display for the menu item You can use the setAlphabeticShortcut() method to assign a shortcut key to the menu item so that users can select an item by pressing a key on the keyboard. The setIcon() method sets an image to be displayed on the menu item. The MenuChoice() method takes a MenuItem argument and checks its ID to determine the menu item that is clicked. It then displays a Toast message to let the user know which menu item was clicked. Options Menu You are now ready to modify the application to display the options menu when the user presses the MENU button on the Android device. Try It Out Displaying an Options Menu 1 . Using the same project created in the previous section, add the following statements in bold to the MainActivity.java file: package net.learn2develop.Menus; import android.app.Activity;
- 211. Using Menus with Views ❘ 189 import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.widget.Button; import android.widget.Toast; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } @Override public boolean onCreateOptionsMenu(Menu menu) { super.onCreateOptionsMenu(menu); CreateMenu(menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { return MenuChoice(item); } private void CreateMenu(Menu menu) { //... } private boolean MenuChoice(MenuItem item) { //... } } 2 . Press F11 to debug the application on the Android Emulator. Figure 5-13 shows the options menu that pops up when you click the MENU button. To select a menu item, either click on an individ- ual item or use its shortcut key (A to D; applicable only to the first four items). How It Works To display the options menu for your activity, you need to override two methods in your activity: onCreateOptionsMenu() and onOptionsItemSelected(). The onCreateOptionsMenu() method is called when the MENU button is pressed. In this event, you call the CreateMenu() helper method to display the options menu. When a menu item is selected, the onOptionsItemSelected() method is called. In this case, you call the MenuChoice() method to display the menu item selected (and do whatever you want to do). Observe the icons displayed for menu items 1, 2, and 3. Also, if the options menu has more than six items, a “More” menu item will be displayed to indicate the additional options. Figure 5-14 shows the additional menu items displayed as a list, after the user has pressed the More menu item.
- 212. 190 ❘ Chapter 5 Displaying Pictures and Menus with Views Figure 5-13 Figure 5-14 Context Menu The previous section showed how the options menu is displayed when the user presses the MENU but- ton. Besides the options menu, you can also display a context menu. A context menu is usually associ- ated with a view on an activity, and it is displayed when the user long clicks an item. For example, if the user taps on a Button view and hold it for a few seconds, a context menu can be displayed.
- 213. Using Menus with Views ❘ 191 If you want to associate a context menu with a view on an activity, you need to call the setOnCreateContextMenuListener() method of that particular view. The following Try It Out shows how you can associate a context menu with a Button view. Try It Out Displaying a Context Menu 1 . Using the same project created in the previous section, add the following statements in bold to the MainActivity.java file: package net.learn2develop.Menus; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.widget.Button; import android.widget.Toast; import android.view.View; import android.view.ContextMenu; import android.view.ContextMenu.ContextMenuInfo; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button btn = (Button) findViewById(R.id.btn1); btn.setOnCreateContextMenuListener(this); } @Override public boolean onCreateOptionsMenu(Menu menu) { super.onCreateOptionsMenu(menu); CreateMenu(menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { return MenuChoice(item); } @Override public void onCreateContextMenu(ContextMenu menu, View view, ContextMenuInfo menuInfo) { super.onCreateContextMenu(menu, view, menuInfo); CreateMenu(menu); } @Override
- 214. 192 ❘ Chapter 5 Displaying Pictures and Menus with Views public boolean onContextItemSelected(MenuItem item) { return MenuChoice(item); } private void CreateMenu(Menu menu) { //... } private boolean MenuChoice(MenuItem item) { //... } } 2 . Press F11 to debug the application on the Android Emulator. Figure 5-15 shows the context menu that is displayed when you long-click the Button view. Figure 5-15 How It Works In the preceding example, you call the setOnCreateContextMenuListener() method of the Button view to associate it with a context menu. When the user long-clicks the Button view, the onCreateContextMenu() method is called. In this method, you call the CreateMenu() method to display the context menu. Similarly, when an item
- 215. Some Additional Views ❘ 193 inside the context menu is selected, the onContextItemSelected() method is called, where you call the MenuChoice() method to display a message to the user. Notice that the shortcut keys for the menu items do not work. To enable the shortcuts keys, you need to call the setQuertyMode() method of the Menu object, like this: private void CreateMenu(Menu menu) { menu.setQwertyMode(true); MenuItem mnu1 = menu.add(0, 0, 0, “Item 1”); { mnu1.setAlphabeticShortcut(‘d’); mnu1.setIcon(R.drawable.icon); } //... } Doing so will enable the shortcut key (see Figure 5-16). Figure 5-16 Some Additional Views Besides the standard views that you have seen up to this point, the Android SDK provides some additional views that make your applications much more interesting. In this section, you will learn more about the following views: AnalogClock, DigitalClock, and WebView.
- 216. 194 ❘ chApter 5 diSPlaYinG PictUreS and menUS with viewS Analogclock and digitalclock views The AnalogClock view displays an analog clock with two hands — one for minutes and one for hours. Its counterpart, the DigitalClock view, displays the time digitally. Both display the system time, and do not allow you to display a particular time. Hence, if you want to display the time for a particular region, you have to build your own custom views. NOTE Creating your own custom views in Android is beyond the scope of this book. However, if you are interested in this area, take a look at Google’s Android documentation on this topic at: http://developer.android.com/guide/topics/ ui/custom-components.html. Using the AnalogClock and DigitalClock views are straightforward; simply declare them in your XML fi le (such as main.xml), like this: <?xmlversion=”1.0”encoding=”utf-8”?> <LinearLayoutxmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <AnalogClock android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> <DigitalClock android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> </LinearLayout> Figure 5-17 shows the AnalogClock and DigitalClock views in action. Webview The WebView enables you to embed a web browser in your activity. This is very useful if your appli- cation needs to embed some web content, such as maps from some other providers, and so on. The following Try It Out shows how you can programmatically load the content of a web page and dis- play it in your activity. try it out Using the WebView View codefile WebView.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it as WebView.
- 217. Some Additional Views ❘ 195 Figure 5-17 2 . Add the following statements to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <WebView android:id=”@+id/webview1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> </LinearLayout> 3 . In the MainActivity.java file, add the following statements in bold: package net.learn2develop.WebView; import android.app.Activity; import android.os.Bundle; import android.webkit.WebSettings; import android.webkit.WebView; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
- 218. 196 ❘ Chapter 5 Displaying Pictures and Menus with Views setContentView(R.layout.main); WebView wv = (WebView) findViewById(R.id.webview1); WebSettings webSettings = wv.getSettings(); webSettings.setBuiltInZoomControls(true); wv.loadUrl( “http://ecx.images-amazon.com/images/I/41HGB-W2Z8L._SL500_AA300_.jpg”); } } 4 . Press F11 to debug the application on the Android Emulator. Figure 5-18 shows the content of the WebView. Figure 5-18 How It Works To use the WebView to load a web page, you use the loadUrl() method, like this: wv.loadUrl( “http://ecx.images-amazon.com/images/I/41HGB-W2Z8L._SL500_AA300_.jpg”); To display the built-in zoom controls, you need to first get the WebSettings property from the WebView and then call its setBuiltInZoomControls() method: WebSettings webSettings = wv.getSettings(); webSettings.setBuiltInZoomControls(true); Figure 5-19 shows the built-in zoom controls that appear when you use the mouse to click and drag the content of the WebView on the Android Emulator.
- 219. Some Additional Views ❘ 197 NOTE While most Android devices support multi-touch screens, the built-in zoom controls are useful for zooming your web content when testing your application on the Android Emulator. Sometimes when you load a page that redirects you (such as load- ing www.wrox.com redirects you to www.wrox.com/wileyCDA), WebView will cause your application to launch the device’s browser applica- tion to load the desired page. For example, if you ask the WebView to load www.wrox.com, Wrox.com will automatically redirect you to www.wrox.com/WileyCDA/. In this case, your application will auto- matically launch the device’s browser application to load your page. In Figure 5-20, note the URL bar at the top of the screen. To prevent this from happening, you need to implement the WebViewClient class and override the shouldOverrideUrlLoading() method, as shown in the following example: packagenet.learn2develop.WebView; Figure 5-19 importandroid.app.Activity; importandroid.os.Bundle; importandroid.webkit.WebSettings; importandroid.webkit.WebView; import android.webkit.WebViewClient; publicclassMainActivityextendsActivity{ /**Calledwhentheactivityisfirstcreated.*/ @Override publicvoidonCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.main); WebViewwv=(WebView)findViewById(R.id.webview1); wv.setWebViewClient(new Callback()); WebSettingswebSettings=wv.getSettings(); webSettings.setBuiltInZoomControls(true); wv.loadUrl(“http://www.wrox.com”); } private class Callback extends WebViewClient { @Override public boolean shouldOverrideUrlLoading(WebView view, String url) { return(false); } } } Figure 5-21 shows the Wrox.com home page now loading correctly in the WebView.
- 220. 198 ❘ Chapter 5 Displaying Pictures and Menus with Views Figure 5-20 Do Figure 5-21 You can also dynamically formulate an HTML string and load it into the WebView, using the loadDataWithBaseURL() method: WebView wv = (WebView) findViewById(R.id.webview1); final String mimeType = “text/html”; final String encoding = “UTF-8”;
- 221. Some Additional Views ❘ 199 String html = “<H1>A simple HTML page</H1><body>” + “<p>The quick brown fox jumps over the lazy dog</p>”; wv.loadDataWithBaseURL(“”, html, mimeType, encoding, “”); Figure 5-22 shows the content displayed by the WebView. Figure 5-22 Alternatively, if you have an HTML file located in the assets folder (see Figure 5-23), you can also load it into the WebView using the loadUrl() method: WebView wv = (WebView) findViewById(R.id.webview1); wv.loadUrl(“file:///android_asset/Index.html”); Figure 5-23
- 222. 200 ❘ Chapter 5 Displaying Pictures and Menus with Views Figure 5-24 shows the content of the WebView. Figure 5-24 Summary In this chapter, you have taken a look at the various views that enable you to display images: Gallery, ImageView, ImageSwitcher, and GridView. In addition, you learned about the difference between options menus and context menus, and how to display them in your application. Finally, you learned about the AnalogClock and DigitalClock views, which display the current time graphi- cally, as well as the WebView, which displays the content of a web page. Exercises 1 . What is the purpose of the ImageSwitcher? 2 . Name the two methods you need to override when implementing an options menu in your activity. 3. Name the two methods you need to override when implementing a context menu in your activity. 4. How do you prevent the WebView from invoking the device’s web browser when a redirection occurs in the WebView? Answers to the Exercises can be found in Appendix C.
- 223. Summary ❘ 201 ⊲⊲ What You Learned In This Chapter Topic Key Concepts Use of the Displays a series of images in a horizontal scrolling list Gallery View Gallery <Gallery android:id=”@+id/gallery1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> ImageView <ImageView android:id=”@+id/image1” android:layout_width=”320px” android:layout_height=”250px” android:scaleType=”fitXY” /> Use of the Performs animation when switching between images ImageSwitcher view ImageSwitcher <ImageSwitcher android:id=”@+id/switcher1” android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:layout_alignParentLeft=”true” android:layout_alignParentRight=”true” android:layout_alignParentBottom=”true” /> Use of the Shows items in a two-dimensional scrolling grid GridView GridView <GridView xmlns:android=”http://schemas.android.com/apk/res/android” android:id=”@+id/gridview” android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:numColumns=”auto_fit” android:verticalSpacing=”10dp” android:horizontalSpacing=”10dp” android:columnWidth=”90dp” android:stretchMode=”columnWidth” android:gravity=”center” /> AnalogClock <AnalogClock android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> DigitalClock <DigitalClock android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> WebView <WebView android:id=”@+id/webview1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” />
- 225. 6 Data Persistence WhAt you Will leArn in thiS chApter ➤➤ How to save simple data using the SharedPreferences object ➤➤ How to write and read files in internal and external storage ➤➤ How to create and use a SQLite database In this chapter, you will learn how to persist data in your Android applications. Persisting data is an important topic in application development, as users expect to reuse the data sometime at a later stage. For Android, there are primarily three basic ways of persisting data: A lightweight mechanism known as shared preferences to save small chunks of data ➤➤ Traditional file systems ➤➤ A relational database management system through the support of SQLite databases The techniques discussed in this chapter enable applications to create and access their own pri- vate data. In the next chapter you’ll learn how you can share data across applications. SAving And loAding uSer preFerenceS Android provides the SharedPreferences object to help you save simple application data. For example, your application may have an option to allow users to specify the font size of the text displayed in your application. In this case, your application needs to remember the size set by the user so that the next time he or she uses the application again, your application can set the size appropriately. In order to do so, you have several options. You can save the data to a file, but you have to perform some fi le management routines, such as writing the data to the fi le, indicating how many characters to read from it, and so on. Also, if you have several pieces of information to save, such as text size, font name, preferred background color, and so on, then the task of writing to a file becomes more onerous.
- 226. 204 ❘ Chapter 6 Data Persistence An alternative to writing to a text file is to use a database, but saving simple data to a database is over- kill, both from a developer’s point of view and in terms of the application’s run-time performance. Using the SharedPreferences object, however, you save the data you want through the use of key/ value pairs — specify a key for the data you want to save, and then both it and its value will be saved automatically to an XML file for you. Using getSharedPreferences() To see how the SharedPreferences object works, the following Try It Out demonstrates how easy it is to save user data to an XML file, and then retrieve it easily via the same object. Try It Out Saving Data Using the SharedPreferences Object codefile SharedPreferences.zip available for download at Wrox.com 1 . Using Eclipse, create an Android project and name it as shown in Figure 6-1. Figure 6-1 2 . Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical”
- 227. Saving and Loading User Preferences ❘ 205 android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <SeekBar android:id=”@+id/SeekBar01” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <TextView android:id=”@+id/TextView01” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”@string/hello” /> <EditText android:id=”@+id/EditText01” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <Button android:id=”@+id/btnSave” android:text=”Save” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> </LinearLayout> 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.SharedPreferences; import android.app.Activity; import android.os.Bundle; import android.content.SharedPreferences; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.SeekBar; import android.widget.SeekBar.OnSeekBarChangeListener; import android.widget.Toast; public class MainActivity extends Activity { private SharedPreferences prefs; private String prefName = “MyPref”; private EditText editText; private SeekBar seekBar; private Button btn; private static final String FONT_SIZE_KEY = “fontsize”; private static final String TEXT_VALUE_KEY = “textvalue”; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); editText = (EditText) findViewById(R.id.EditText01); seekBar = (SeekBar) findViewById(R.id.SeekBar01);
- 228. 206 ❘ Chapter 6 Data Persistence btn = (Button) findViewById(R.id.btnSave); btn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //---get the SharedPreferences object--- prefs = getSharedPreferences(prefName, MODE_PRIVATE); SharedPreferences.Editor editor = prefs.edit(); //---save the values in the EditText view to preferences--- editor.putFloat(FONT_SIZE_KEY, editText.getTextSize()); editor.putString(TEXT_VALUE_KEY, editText.getText().toString()); //---saves the values--- editor.commit(); //---display file saved message--- Toast.makeText(getBaseContext(), “Font size saved successfully!”, Toast.LENGTH_SHORT).show(); } }); //---load the SharedPreferences object--- SharedPreferences prefs = getSharedPreferences(prefName, MODE_PRIVATE); //---set the TextView font size to the previously saved values--- float fontSize = prefs.getFloat(FONT_SIZE_KEY, 12); //---init the SeekBar and EditText--- seekBar.setProgress((int) fontSize); editText.setText(prefs.getString(TEXT_VALUE_KEY, “”)); editText.setTextSize(seekBar.getProgress()); seekBar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() { @Override public void onStopTrackingTouch(SeekBar seekBar) { } @Override public void onStartTrackingTouch(SeekBar seekBar) { } @Override public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) { //---change the font size of the EditText--- editText.setTextSize(progress); } }); } } 4 . Press F11 to debug the application on the Android Emulator.
- 229. Saving and Loading User Preferences ❘ 207 5 . Enter some text into the EditText view and then change its font size by adjusting the SeekBar view (see Figure 6-2). Click Save. Figure 6-2 6 . Return to Eclipse and press F11 to debug the application on the Android Emulator again. The application now displays the same text that you entered earlier using the same font size set earlier. How It Works To use the SharedPreferences object, you use the getSharedPreferences() method, passing it the name of the shared preferences file (in which all the data will be saved), as well as the mode in which it should be opened: private SharedPreferences prefs; ... //---get the SharedPreferences object--- prefs = getSharedPreferences(prefName, MODE_PRIVATE); SharedPreferences.Editor editor = prefs.edit(); The MODE_PRIVATE constant indicates that the shared preference file can only be opened by the applica- tion that created it. The Editor class allows you to save key/value pairs to the preferences file by exposing methods such as the following: ➤➤ putString() ➤➤ putBoolean() ➤➤ putLong()
- 230. 208 ❘ Chapter 6 Data Persistence ➤➤ putInt() ➤➤ putFloat() When you are done saving the values, call the commit() method to save the changes: //---save the values in the EditText view to preferences--- editor.putFloat(FONT_SIZE_KEY, editText.getTextSize()); editor.putString(TEXT_VALUE_KEY, editText.getText().toString()); //---saves the values--- editor.commit(); When the activity is loaded, you first obtain the SharedPreferences object and then retrieve all the val- ues saved earlier: //---load the SharedPreferences object--- SharedPreferences prefs = getSharedPreferences(prefName, MODE_PRIVATE); //---set the TextView font size to the previously saved values--- float fontSize = prefs.getFloat(FONT_SIZE_KEY, 12); //---init the SeekBar and EditText--- seekBar.setProgress((int) fontSize); editText.setText(prefs.getString(TEXT_VALUE_KEY, “”)); editText.setTextSize(seekBar.getProgress()); The shared preferences file is saved as an XML file in the /data/ data/<package_name>/shared_prefs folder (see Figure 6-3). Its content is shown here (formatted for clarity): Figure 6-3 <?xml version=’1.0’ encoding=’utf-8’ standalone=’yes’ ?> <map> <string name=”textvalue”>This is so cool!</string> <float name=”fontsize” value=”75.0” /> </map> Using getPreferences() In the previous section, you used the used the SharedPreferences object by supplying it with a name, like this: //---get the SharedPreferences object--- prefs = getSharedPreferences(prefName, MODE_PRIVATE); In this case, the information saved inside the SharedPreferences object is visible to all the activities within the same application. However, if you don’t need to share the data between activities, you can use the getPreferences() method, like this: //---get the SharedPreferences object--- prefs = getPreferences(MODE_PRIVATE);
- 231. Persisting Data to Files ❘ 209 The getPreferences() method does not require a name, and the data saved is restricted to the activity that created it. In this case, the file- name used for the preferences file will be named after the activity that created it (see Figure 6-4). Figure 6-4 Persisting Data to Files The SharedPreferences object allows you to store data that could best be stored as key/value pairs, for example, data such as user ID, birthdate, gender, driving license number, etc. However, some- times you might prefer to use the traditional file system to store your data. For example, you might want to store text of poems that you want to display in your applications. In Android, you can use the classes in the java.io namespace to do so. Saving to Internal Storage The first way to save files in your Android application is to write to the device’s internal storage. The fol- lowing Try It Out demonstrates how to save a string entered by the user to the device’s internal storage. Try It Out Saving Data to Internal Storage codefile Files.zip available for download at Wrox.com 1 . Using Eclipse, create an Android project and name it as shown in Figure 6-5. 2 . In the main.xml file, add the following statements in bold: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Please enter some text” /> <EditText android:id=”@+id/txtText1” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <Button android:id=”@+id/btnSave” android:text=”Save” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <Button android:id=”@+id/btnLoad” android:text=”Load” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> </LinearLayout>
- 232. 210 ❘ Chapter 6 Data Persistence Figure 6-5 3 . In the MainActivity.java file, add the following statements in bold: package net.learn2develop.Files; import android.app.Activity; import android.view.View; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStreamReader; import java.io.OutputStreamWriter; import android.os.Bundle; import android.widget.Button; import android.widget.EditText; import android.widget.Toast; public class MainActivity extends Activity { private EditText textBox; private static final int READ_BLOCK_SIZE = 100; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); textBox = (EditText) findViewById(R.id.txtText1);
- 233. Persisting Data to Files ❘ 211 Button saveBtn = (Button) findViewById(R.id.btnSave); Button loadBtn = (Button) findViewById(R.id.btnLoad); saveBtn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { String str = textBox.getText().toString(); try { FileOutputStream fOut = openFileOutput(“textfile.txt”, MODE_WORLD_READABLE); OutputStreamWriter osw = new OutputStreamWriter(fOut); //---write the string to the file--- osw.write(str); osw.flush(); osw.close(); //---display file saved message--- Toast.makeText(getBaseContext(), “File saved successfully!”, Toast.LENGTH_SHORT).show(); //---clears the EditText--- textBox.setText(“”); } catch (IOException ioe) { ioe.printStackTrace(); } } }); loadBtn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { try { FileInputStream fIn = openFileInput(“textfile.txt”); InputStreamReader isr = new InputStreamReader(fIn); char[] inputBuffer = new char[READ_BLOCK_SIZE]; String s = “”; int charRead; while ((charRead = isr.read(inputBuffer))>0) { //---convert the chars to a String--- String readString = String.copyValueOf(inputBuffer, 0, charRead); s += readString; inputBuffer = new char[READ_BLOCK_SIZE];
- 234. 212 ❘ Chapter 6 Data Persistence } //---set the EditText to the text that has been // read--- textBox.setText(s); Toast.makeText(getBaseContext(), “File loaded successfully!”, Toast.LENGTH_SHORT).show(); } catch (IOException ioe) { ioe.printStackTrace(); } } }); } } 4 . Press F11 to debug the application on the Android Emulator. 5. Type some text into the EditText view (see Figure 6-6) and then click the Save button. Figure 6-6 6 . If the file is saved successfully, you will see the Toast class displaying the “File saved successfully!” message. The text in the EditText view should disappear. 7. Click the Load button and you should see the string appearing in the EditText view again. This confirms that the text is saved correctly.
- 235. Persisting Data to Files ❘ 213 How It Works To save text into a file, you use the FileOutputStream class. The openFileOutput() method opens a named file for writing, with the mode specified. In this example, you use the MODE_WORLD_READABLE constant to indicate that the file is readable by all other applications: FileOutputStream fOut = openFileOutput(“textfile.txt”, MODE_WORLD_READABLE); Apart from the MODE_WORLD_READABLE constant, you can select from the following: MODE_PRIVATE (file can only be accessed by the application that created it), MODE_APPEND (for appending to an existing file), and MODE_WORLD_WRITEABLE (all other applications have write access to the file). To convert a character stream into a byte stream, you use an instance of the OutputStreamWriter class, by passing it an instance of the FileOutputStream object: OutputStreamWriter osw = new OutputStreamWriter(fOut); You then use its write() method to write the string to the file. To ensure that all the bytes are written to the file, use the flush() method. Finally, use the close() method to close the file: osw.write(str); osw.flush(); osw.close(); To read the content of a file, you use the FileInputStream class, together with the InputStreamReader class: FileInputStream fIn = openFileInput(“textfile.txt”); InputStreamReader isr = new InputStreamReader(fIn); As you do not know the size of the file to read, the content is read in blocks of 100 characters into a buffer (character array). The characters read are then copied into a String object: char[] inputBuffer = new char[READ_BLOCK_SIZE]; String s = “”; int charRead; while ((charRead = isr.read(inputBuffer))>0) { //---convert the chars to a String--- String readString = String.copyValueOf(inputBuffer, 0, charRead); s += readString; inputBuffer = new char[READ_BLOCK_SIZE]; } The read() method of the InputStreamReader object reads the number of characters read and returns -1 if the end of the file is reached.
- 236. 214 ❘ Chapter 6 Data Persistence When testing this application on the Android Emulator, you can use the DDMS to verify that the appli- cation did indeed save the file into the application’s files directory (see Figure 6-7; the actual directory is /data/data/net.learn2develop.Files/files) Figure 6-7 Saving to External Storage (SD Card) The previous section showed how you can save your files to the internal storage of your Android device. Sometimes, it would be useful to save them to external storage (such as an SD card) because of its larger capacity, as well as the capability to share the files easily with other users (by removing the SD card and passing it to somebody else). Using the project created in the previous section as the example, to save the text entered by the user in the SD card, modify the onClick() method of the Save button as shown in bold here: saveBtn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { String str = textBox.getText().toString(); try { //---SD Card Storage--- File sdCard = Environment.getExternalStorageDirectory(); File directory = new File (sdCard.getAbsolutePath() + “/MyFiles”); directory.mkdirs(); File file = new File(directory, “textfile.txt”); FileOutputStream fOut = new FileOutputStream(file); OutputStreamWriter osw = new OutputStreamWriter(fOut); //---write the string to the file--- osw.write(str); osw.flush();
- 237. Persisting Data to Files ❘ 215 osw.close(); //---display file saved message--- Toast.makeText(getBaseContext(), “File saved successfully!”, Toast.LENGTH_SHORT).show(); //---clears the EditText--- textBox.setText(“”); } catch (IOException ioe) { ioe.printStackTrace(); } } }); The preceding code uses the getExternalStorageDirectory() method to return the full path to the external storage. Typically, it should return the “/sdcard” path for a real device, and “/mnt/sdcard” for an Android Emulator. However, you should never try to hardcode the path to the SD card, as manufacturers may choose to assign a different path name to the SD card. Hence, be sure to use the getExternalStorageDirectory() method to return the full path to the SD card. You then create a directory called MyFiles in the SD card. Finally, you save the file into this directory. To load the file from the external storage, modify the onClick() method for the Load button: loadBtn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { try { //---SD Storage--- File sdCard = Environment.getExternalStorageDirectory(); File directory = new File (sdCard.getAbsolutePath() + “/MyFiles”); File file = new File(directory, “textfile.txt”); FileInputStream fIn = new FileInputStream(file); InputStreamReader isr = new InputStreamReader(fIn); char[] inputBuffer = new char[READ_BLOCK_SIZE]; String s = “”; int charRead; while ((charRead = isr.read(inputBuffer))>0) { //---convert the chars to a String--- String readString = String.copyValueOf(inputBuffer, 0, charRead); s += readString; inputBuffer = new char[READ_BLOCK_SIZE]; } //---set the EditText to the text that has been // read---
- 238. 216 ❘ Chapter 6 Data Persistence textBox.setText(s); Toast.makeText(getBaseContext(), “File loaded successfully!”, Toast.LENGTH_SHORT).show(); } catch (IOException ioe) { ioe.printStackTrace(); } } }); Note that in order to write to the external storage, you need to add the WRITE_EXTERNAL_STORAGE permission in your AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Files” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”9” /> <uses-permission android:name=”android.permission.WRITE_EXTERNAL_STORAGE”> </uses-permission> </manifest> Choosing the Best Storage Option And so, you have seen the few ways of saving data in your Android applications — SharedPreferences, internal storage, and external storage. Which one should you use in your applications? Here are some suggestions: ➤➤ If you have data that can be represented using key/value pairs, then use the SharedPreferences object. For example, if you want to store user preference data such as user name, background color, date of birth, last login date, then the SharedPreferences object is the ideal way to store these data. Moreover, you don’t really have to get your hands dirty on how these data are stored; all you need is to use the SharedPreferences object to store and retrieve them. ➤➤ If you need to store ad-hoc data, then using the internal storage is a good option. For exam- ple, your application (such as an RSS reader) may need to download images from the Web for display. In this scenario, saving the images to internal storage is a good solution. You may also need to persist data created by the user, such as when you have a note-taking appli- cation where users can take notes and save them for later use. In all these scenarios, using the internal storage is a good choice.
- 239. Persisting Data to Files ❘ 217 ➤➤ There are times when you need to share your application data with other users. For example, you may create an Android application that logs the coordinates of the locations that a user has been to, and you want to share all these data with other users. In this scenario, you can store your files on the SD card of the device so that users can easily transfer the data to other devices (and computers) for use later. Using Static Resources Besides creating and using files dynamically during run time, it is also possible to add files to your package during design time so that you can use it during run time. For example, you may want to bundle some help files with your package so that you can display some help messages when users need it. In this case, you can add the files to the res/raw folder (you need to create this folder yourself) of your pack- age. Figure 6-8 shows the res/raw folder containing a file named textfile.txt. To make use of the file in code, use the getResources() method to return a Figure 6-8 Resources object and then use its openRawResource() method to open the file contained in the res/raw folder: import java.io.InputStream; import java.io.BufferedReader; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); InputStream is = this.getResources().openRawResource(R.raw.textfile); BufferedReader br = new BufferedReader(new InputStreamReader(is)); String str = null; try { while ((str = br.readLine()) != null) { Toast.makeText(getBaseContext(), str, Toast.LENGTH_SHORT).show(); } is.close(); br.close(); } catch (IOException e) { e.printStackTrace(); } textBox = (EditText) findViewById(R.id.txtText1); Button saveBtn = (Button) findViewById(R.id.btnSave); Button loadBtn = (Button) findViewById(R.id.btnLoad); saveBtn.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { } }); loadBtn.setOnClickListener(new View.OnClickListener() {
- 240. 218 ❘ Chapter 6 Data Persistence public void onClick(View v) { } }); } The resource ID of the resource stored in the res/raw folder is named after its filename without its extension. For example, if the text file is textfile.txt, then its resource ID is R.raw.textfile. Creating and Using Databases So far, all the techniques you have seen are useful for saving simple sets of data. For saving relational data, using a database is much more efficient. For example, if you want to store the results of all the students in a school, it is much more efficient to use a database to represent them because you can use database querying to retrieve the results of the specific students. Moreover, using databases enables you to enforce data integrity by specifying the relationships between different sets of data. Android uses the SQLite database system. The database that you create for an application is only acces- sible to itself; other applications will not be able to access it. In this section, you will learn how to programmatically create a SQLite database in your Android application. For Android, the SQLite database that you create programmatically in an application is always stored in the /data/data/<package_name>/databases folder. Creating the DBAdapter Helper Class A good practice for dealing with databases is to create a helper class to encapsulate all the complexi- ties of accessing the data so that it is transparent to the calling code. Hence, for this section, you will create a helper class called DBAdapter that creates, opens, closes, and uses a SQLite database. Do In this example, you are going to create a database named MyDB contain- ing one table named contacts. This table will have three columns: _id, name, and email (see Figure 6-9). Figure 6-9 Try It Out Creating the Database Helper Class codefile Databases.zip available for download at Wrox.com 1 . Using Eclipse, create an Android project and name it Databases. 2 . Add a new class file to the project and name it DBAdapter.java (see Figure 6-10). 3. Add the following statements in bold to the DBAdapter.java file: Figure 6-10 package net.learn2develop.Databases; import android.content.ContentValues; import android.content.Context;
- 241. Creating and Using Databases ❘ 219 import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.util.Log; public class DBAdapter { public static final String KEY_ROWID = “_id”; public static final String KEY_NAME = “name”; public static final String KEY_EMAIL = “email”; private static final String TAG = “DBAdapter”; private static final String DATABASE_NAME = “MyDB”; private static final String DATABASE_TABLE = “contacts”; private static final int DATABASE_VERSION = 1; private static final String DATABASE_CREATE = “create table contacts (_id integer primary key autoincrement, “ + “name text not null, email text not null);”; private final Context context; private DatabaseHelper DBHelper; private SQLiteDatabase db; public DBAdapter(Context ctx) { this.context = ctx; DBHelper = new DatabaseHelper(context); } private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { try { db.execSQL(DATABASE_CREATE); } catch (SQLException e) { e.printStackTrace(); } } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, “Upgrading database from version “ + oldVersion + “ to “ + newVersion + “, which will destroy all old data”); db.execSQL(“DROP TABLE IF EXISTS contacts”);
- 242. 220 ❘ Chapter 6 Data Persistence onCreate(db); } } //---opens the database--- public DBAdapter open() throws SQLException { db = DBHelper.getWritableDatabase(); return this; } //---closes the database--- public void close() { DBHelper.close(); } //---insert a contact into the database--- public long insertContact(String name, String email) { ContentValues initialValues = new ContentValues(); initialValues.put(KEY_NAME, name); initialValues.put(KEY_EMAIL, email); return db.insert(DATABASE_TABLE, null, initialValues); } //---deletes a particular contact--- public boolean deleteContact(long rowId) { return db.delete(DATABASE_TABLE, KEY_ROWID + “=” + rowId, null) > 0; } //---retrieves all the contacts--- public Cursor getAllContacts() { return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME, KEY_EMAIL}, null, null, null, null, null); } //---retrieves a particular contact--- public Cursor getContact(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME, KEY_EMAIL}, KEY_ROWID + “=” + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; } //---updates a contact--- public boolean updateContact(long rowId, String name, String email)
- 243. Creating and Using Databases ❘ 221 { ContentValues args = new ContentValues(); args.put(KEY_NAME, name); args.put(KEY_EMAIL, email); return db.update(DATABASE_TABLE, args, KEY_ROWID + “=” + rowId, null) > 0; } } How It Works You first defined several constants to contain the various fields for the table that you are going to create in your database: public static final String KEY_ROWID = “_id”; public static final String KEY_NAME = “name”; public static final String KEY_EMAIL = “email”; private static final String TAG = “DBAdapter”; private static final String DATABASE_NAME = “MyDB”; private static final String DATABASE_TABLE = “contacts”; private static final int DATABASE_VERSION = 1; private static final String DATABASE_CREATE = “create table contacts (_id integer primary key autoincrement, “ + “name text not null, email text not null);”; In particular, the DATABASE_CREATE constant contains the SQL statement for creating the contacts table within the MyDB database. Within the DBAdapter class, you also extend the SQLiteOpenHelper class, which is a helper class in Android to manage database creation and version management. In particular, you override the onCreate() and onUpgrade() methods: public class DBAdapter { public static final String KEY_ROWID = “_id”; public static final String KEY_NAME = “name”; public static final String KEY_EMAIL = “email”; private static final String TAG = “DBAdapter”; private static final String DATABASE_NAME = “MyDB”; private static final String DATABASE_TABLE = “contacts”; private static final int DATABASE_VERSION = 1; private static final String DATABASE_CREATE = “create table contacts (_id integer primary key autoincrement, “ + “name text not null, email text not null);”; private final Context context; private DatabaseHelper DBHelper; private SQLiteDatabase db; public DBAdapter(Context ctx) {
- 244. 222 ❘ Chapter 6 Data Persistence this.context = ctx; DBHelper = new DatabaseHelper(context); } private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { try { db.execSQL(DATABASE_CREATE); } catch (SQLException e) { e.printStackTrace(); } } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, “Upgrading database from version “ + oldVersion + “ to “ + newVersion + “, which will destroy all old data”); db.execSQL(“DROP TABLE IF EXISTS contacts”); onCreate(db); } } The onCreate() method creates a new database if the required database is not present. The onUpgrade() method is called when the database needs to be upgraded. This is achieved by checking the value defined in the DATABASE_VERSION constant. For this implementation of the onUpgrade() method, you simply drop the table and create it again. You can then define the various methods for opening and closing the database, as well as the methods for adding/editing/deleting rows in the table: public class DBAdapter { //... //... //---opens the database--- public DBAdapter open() throws SQLException { db = DBHelper.getWritableDatabase(); return this; } //---closes the database--- public void close() {
- 245. Creating and Using Databases ❘ 223 DBHelper.close(); } //---insert a contact into the database--- public long insertContact(String name, String email) { ContentValues initialValues = new ContentValues(); initialValues.put(KEY_NAME, name); initialValues.put(KEY_EMAIL, email); return db.insert(DATABASE_TABLE, null, initialValues); } //---deletes a particular contact--- public boolean deleteContact(long rowId) { return db.delete(DATABASE_TABLE, KEY_ROWID + “=” + rowId, null) > 0; } //---retrieves all the contacts--- public Cursor getAllContacts() { return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME, KEY_EMAIL}, null, null, null, null, null); } //---retrieves a particular contact--- public Cursor getContact(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME, KEY_EMAIL}, KEY_ROWID + “=” + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; } //---updates a contact--- public boolean updateContact(long rowId, String name, String email) { ContentValues args = new ContentValues(); args.put(KEY_NAME, name); args.put(KEY_EMAIL, email); return db.update(DATABASE_TABLE, args, KEY_ROWID + “=” + rowId, null) > 0; } } Notice that Android uses the Cursor class as a return value for queries. Think of the Cursor as a pointer to the result set from a database query. Using Cursor enables Android to more efficiently manage rows and columns as needed. You use a ContentValues object to store key/value pairs. Its put() method enables you to insert keys with values of different data types.
- 246. 224 ❘ Chapter 6 Data Persistence Using the Database Programmatically You are now ready to use the database using the helper class created in the previous section. Adding Contacts The following Try It Out demonstrates how you can add a contact to the table. Try It Out Adding Contacts to a Table 1 . Using the same project created earlier, add the following statements in bold to the MainActivity .java file: package net.learn2develop.Databases; import android.app.Activity; import android.os.Bundle; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); DBAdapter db = new DBAdapter(this); //---add a contact--- db.open(); long id = db.insertContact(“Wei-Meng Lee”, “[email protected]”); id = db.insertContact(“Mary Jackson”, “[email protected]”); db.close(); } } 2 . Press F11 to debug the application on the Android Emulator. How It Works In this example, you first created an instance of the DBAdapter class: DBAdapter db = new DBAdapter(this); The insertContact() method returns the ID of the inserted row. If an error occurs during the operation, it returns -1. If you examine the file system of the Android device/emulator using DDMS, you can see that the MyDB database is created under the databases folder (see Figure 6-11). Figure 6-11
- 247. Creating and Using Databases ❘ 225 Retrieving All the Contacts To retrieve all the contacts in the contacts table, use the getAllContacts() method of the DBAdapter class, as the following Try It Out shows. Try It Out Retrieving All Contacts from a Table 1 . Using the same project created earlier, add the following statements in bold to the MainActivity .java file: package net.learn2develop.Databases; import android.app.Activity; import android.os.Bundle; import android.widget.Toast; import android.database.Cursor; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); DBAdapter db = new DBAdapter(this); /* //---add a contact--- db.open(); long id = db.insertContact(“Wei-Meng Lee”, “[email protected]”); id = db.insertContact(“Mary Jackson”, “[email protected]”); db.close(); */ //---get all contacts--- db.open(); Cursor c = db.getAllContacts(); if (c.moveToFirst()) { do { DisplayContact(c); } while (c.moveToNext()); } db.close(); } public void DisplayContact(Cursor c) { Toast.makeText(this, “id: “ + c.getString(0) + “n” +
- 248. 226 ❘ Chapter 6 Data Persistence “Name: “ + c.getString(1) + “n” + “Email: “ + c.getString(2), Toast.LENGTH_LONG).show(); } } 2 . Press F11 to debug the application on the Android Emulator. Figure 6-12 shows the Toast class displaying the contacts retrieved from the database. Figure 6-12 How It Works The getAllContacts() method of the DBAdapter class retrieves all the contacts stored in the database. The result is returned as a Cursor object. To display all the contacts, you first need to call the moveToFirst() method of the Cursor object. If it succeeds (which means at least one row is available), display the details of the contact using the DisplayContact() method. To move to the next contact, call the moveToNext() method of the Cursor object. Retrieving a Single Contact To retrieve a single contact using its ID, call the getContact() method of the DBAdapter class, as the following Try It Out shows.
- 249. Creating and Using Databases ❘ 227 Try It Out Retrieving a Contact from a Table 1 . Using the same project created earlier, add the following statements in bold to the MainActivity .java file: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); DBAdapter db = new DBAdapter(this); /* //---add a contact--- //... */ /* //---get all contacts--- //... */ //---get a contact--- db.open(); Cursor c = db.getContact(2); if (c.moveToFirst()) DisplayContact(c); else Toast.makeText(this, “No contact found”, Toast.LENGTH_LONG).show(); db.close(); } 2 . Press F11 to debug the application on the Android Emulator. The details of the second contact will be displayed using the Toast class. How It Works The getContact() method of the DBAdapter class retrieves a single contact using its ID. You passed in the ID of the contact; in this case, you passed in an ID of 2 to indicate that you want to retrieve the second contact: Cursor c = db.getContact(2); The result is returned as a Cursor object. If a row is returned, you display the details of the contact using the DisplayContact() method; otherwise, you display a message using the Toast class. Updating a Contact To update a particular contact, call the updateContact() method in the DBAdapter class by passing the ID of the contact you want to update, as the following Try It Out shows.
- 250. 228 ❘ Chapter 6 Data Persistence Try It Out Updating a Contact in a Table 1 . Using the same project created earlier, add the following statements in bold to the MainActivity .java file: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); DBAdapter db = new DBAdapter(this); /* //---add a contact--- //... */ /* //---get all contacts--- //... */ /* //... */ //---update contact--- db.open(); if (db.updateContact(1, “Wei-Meng Lee”, “[email protected]”)) Toast.makeText(this, “Update successful.”, Toast.LENGTH_LONG).show(); else Toast.makeText(this, “Update failed.”, Toast.LENGTH_LONG).show(); db.close(); } 2 . Press F11 to debug the application on the Android Emulator. A message will be displayed if the update is successful. How It Works The updateContact() method in the DBAdapter class updates a contact’s details by using the ID of the contact you want to update. It returns a Boolean value, indicating whether the update was successful. Deleting a Contact To delete a contact, use the deleteContact() method in the DBAdapter class by passing the ID of the contact you want to update, as the following Try It Out shows.
- 251. Creating and Using Databases ❘ 229 Try It Out Deleting a Contact from a Table 1 . Using the same project created earlier, add the following statements in bold to the MainActivity .java file: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); DBAdapter db = new DBAdapter(this); /* //---add a contact--- //... */ /* //---get all contacts--- //... */ /* //---get a contact--- //... */ /* //---update contact--- //... */ //---delete a contact--- db.open(); if (db.deleteContact(1)) Toast.makeText(this, “Delete successful.”, Toast.LENGTH_LONG).show(); else Toast.makeText(this, “Delete failed.”, Toast.LENGTH_LONG).show(); db.close(); } 2 . Press F11 to debug the application on the Android Emulator. A message will be displayed if the deletion was successful. How It Works The deleteContact() method in the DBAdapter class deletes a contact using the ID of the contact you want to update. It returns a Boolean value, indicating whether the deletion was successful.
- 252. 230 ❘ Chapter 6 Data Persistence Upgrading the Database Sometimes, after creating and using the database, you may need to add additional tables, change the schema of the database, or add columns to your tables. In this case, you need to migrate your exist- ing data from the old database to a newer one. To upgrade the database, change the DATABASE_VERSION constant to a value higher than the previous one. For example, if its previous value was 1, change it to 2: public class DBAdapter { public static final String KEY_ROWID = “_id”; public static final String KEY_NAME = “name”; public static final String KEY_EMAIL = “email”; private static final String TAG = “DBAdapter”; private static final String DATABASE_NAME = “MyDB”; private static final String DATABASE_TABLE = “contacts”; private static final int DATABASE_VERSION = 2; When you run the application one more time, you will see the following message in the LogCat win- dow of Eclipse: DBAdapter(24096): Upgrading database from version 1 to 2, which will destroy all old data In this example, for simplicity you simply drop the existing table and create a new one. In real-life, you usually back up your existing table and then copy them over to the new table. Pre-Creating the Database In real-life applications, sometimes it would be more efficient to pre-create the database at design time rather than run time. To pre-create a SQLite database, you can use many of the free tools avail- able on the Internet. One such tool is the SQLite Database Browser, which is available free for the different platforms (http://sourceforge.net/projects/sqlitebrowser/). Once you have installed the SQLite Database Browser, you can create a database visually. Figure 6-13 shows that I have created a contacts table with the fields indicated. Figure 6-13
- 253. Creating and Using Databases ❘ 231 Populating the table with rows is also straightforward. Figure 6-14 shows how you can fi ll the table with data using the Browse Data tab. Figure 6-14 Bundling the Database with an Application With the database created at design time, the next thing you should do is bundle it together with your application so that you can use it in your application. The following Try It Out shows you how. try it out Bundling a Database 1 . Using the same project created earlier, drag and drop the SQLite database file that you have created in the previous section into the assets folder in your Android project in Eclipse (see Figure 6-15). Figure 6-15 NOTE Note that a filename for files added to the assets folder must be in lower- case letters. As such, a filename such as MyDB is invalid, whereas mydb is fine. 2 . Add the following statements in bold to the MainActivity.java file: @Override Prepared for RICHARD SALDANA/ email0 [email protected] Order number0 82951548 This PDF is for the purchaser’s personal use in accordance with the Wrox Terms of Service and under US copyright as stated on this book’s copyright page. If you did not purchase this copy/ please visit www.wrox.com to purchase your own copy.
- 254. 232 ❘ Chapter 6 Data Persistence public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); try { String destPath = “/data/data/” + getPackageName() + “/databases/MyDB”; File f = new File(destPath); if (!f.exists()) { CopyDB( getBaseContext().getAssets().open(“mydb”), new FileOutputStream(destPath)); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } DBAdapter db = new DBAdapter(this); //---get all contacts--- db.open(); Cursor c = db.getAllContacts(); if (c.moveToFirst()) { do { DisplayContact(c); } while (c.moveToNext()); } db.close(); } public void CopyDB(InputStream inputStream, OutputStream outputStream) throws IOException { //---copy 1K bytes at a time--- byte[] buffer = new byte[1024]; int length; while ((length = inputStream.read(buffer)) > 0) { outputStream.write(buffer, 0, length); } inputStream.close(); outputStream.close(); } 3 . Press F11 to debug the application on the Android Emulator. When the application runs, it will copy the mydb database file into the /data/data/net.learn2develop.Databases/databases/ folder with the name MyDB. How It Works You first defined the CopyDB() method to copy the database file from one location to another: public void CopyDB(InputStream inputStream,
- 255. Creating and Using Databases ❘ 233 OutputStream outputStream) throws IOException { //---copy 1K bytes at a time--- byte[] buffer = new byte[1024]; int length; while ((length = inputStream.read(buffer)) > 0) { outputStream.write(buffer, 0, length); } inputStream.close(); outputStream.close(); } Note that in this case you used the InputStream object to read from the source file, and then wrote it to the destination file using the OutputStream object. When the activity is created, you copy the database file located in the assets folder into the /data/data/ net.learn2develop.Databases/databases/ folder on the Android device (or emulator): try { String destPath = “/data/data/” + getPackageName() + “/databases/MyDB”; File f = new File(destPath); if (!f.exists()) { CopyDB( getBaseContext().getAssets().open(“mydb”), new FileOutputStream(destPath)); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } You copy the database file only if it does not exist in the destination folder. If you don’t perform this check, every time the activity is created you will overwrite the database file with the one in the assets folder. This may not be desirable, as your application may make changes to the database file during run time, and this will wipe out all the changes you have made so far. To ensure that the database file is indeed copied, be sure to delete the database file in your emulator (if it already existed) prior to testing the application. You can delete the database using DDMS (see Figure 6-16). Figure 6-16
- 256. 234 ❘ Chapter 6 Data Persistence Summary In this chapter, you learned the different ways to save persistent data to your Android device. For sim- ple unstructured data, using the SharedPreferences object is the ideal solution. If you need to store bulk data, then consider using the traditional file system. Finally, for structured data, it is more efficient to store it in a relational database management system. For this, Android provides the SQLite database, which you can access easily using the APIs exposed. Note that for the SharedPreferences object and the SQLite database, the data is accessible only by the application that creates it. In other words, it is not shareable. If you need to share data among different applications, you need to create a content provider. Content providers are discussed in more detail in the next chapter. Exercises 1 . What is the difference between the getSharedPreferences() and getPreferences() methods? . 2 Name the method that enables you to obtain the path of the external storage of an Android device. . 3 What is the permission you need to declare when writing files to external storage? Answers to Exercises can be found in Appendix C.
- 257. Summary ❘ 235 ⊲⊲ What You Learned In This Chapter Topic Key Concepts Save simple user data Use the SharedPreferences object. Sharing data among activities Use the getSharedPreferences() method. in the same application Saving data visible only to the Use the getPreferences() method. activity that created it Saving to file Use the FileOutputStream and OutputStreamReader classes. Reading from file Use the FileInputStream and InputStreamReader classes. Saving to external storage Use the getExternalStorageDirectory() method to return the path to the external storage. Accessing files in the res/raw Use the openRawResource() method in the Resources object folder (obtained via the getResources() method). Creating a database helper Extend the SQLiteOpenHelper class. class
- 259. 7 Content Providers WhAt you Will leArn in thiS chApter ➤➤ What are content providers? ➤➤ How to use a content provider in Android ➤➤ How to create your own content provider ➤➤ How to use your own content provider In the previous chapter, you learned about the various ways to persist data — using shared preferences, files, as well as SQLite databases. While using the database approach is the recom- mended way to save structured and complex data, sharing data is a challenge because the data- base is accessible to only the package that created it. In this chapter, you will learn Android’s way of sharing data through the use of content pro- viders. You will learn how to use the built-in content providers, as well as implement your own content providers to share data across packages. ShAring dAtA in Android In Android, using a content provider is the recommended way to share data across packages. Think of a content provider as a data store. How it stores its data is not relevant to the appli- cation using it; what is important is how packages can access the data stored in it using a con- sistent programming interface. A content provider behaves very much like a database — you can query it, edit its content, as well as add or delete its content. However, unlike a database, a content provider can use different ways to store its data. The data can be stored in a database, in fi les, or even over a network. Android ships with many useful content providers, including the following: ➤➤ Browser — Stores data such as browser bookmarks, browser history, and so on ➤➤ CallLog — Stores data such as missed calls, call details, and so on
- 260. 238 ❘ Chapter 7 Content Providers ➤➤ Contacts — Stores contact details ➤➤ MediaStore — Stores media files such as audio, video and images ➤➤ Settings — Stores the device’s settings and preferences Besides the many built-in content providers, you can also create your own content providers. To query a content provider, you specify the query string in the form of a URI, with an optional specifier for a particular row. The format of the query URI is as follows: <standard_prefix>://<authority>/<data_path>/<id> The various parts of the URI are as follows: ➤➤ The standard prefix for content providers is always content://. ➤➤ The authority specifies the name of the content provider. An example would be contacts for the built-in Contacts content provider. For third-party content providers, this could be the fully qualified name, such as com.wrox.provider or net.learn2develop.provider. ➤➤ The data path specifies the kind of data requested. For example, if you are getting all the con- tacts from the Contacts content provider, then the data path would be people, and the URI would look like this: content://contacts/people. ➤➤ The id specifies the specific record requested. For example, if you are looking for contact number 2 in the Contacts content provider, the URI would look like this: content:// contacts/people/2. Table 7-1 shows some examples of query strings. Table 7-1: xample Query Strings E Query String Description content://media/internal/images Returns a list of all the internal images on the device content://media/external/images Returns a list of all the images stored on the external storage (e.g., SD card) on the device content://call_log/calls Returns a list of all calls registered in the Call Log content://browser/bookmarks Returns a list of bookmarks stored in the browser Using a Content Provider The best way to understand content providers is to actually use one. The following Try It Out shows how you can use a content provider from within your Android application.
- 261. Using a Content Provider ❘ 239 Try It Out Using the Contacts Content Provider codefile Provider.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it as shown in Figure 7-1. Figure 7-1 2 . Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <ListView android:id=”@+id/android:list”
- 262. 240 ❘ Chapter 7 Content Providers android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:layout_weight=”1” android:stackFromBottom=”false” android:transcriptMode=”normal” /> <TextView android:id=”@+id/contactName” android:textStyle=”bold” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> <TextView android:id=”@+id/contactID” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> </LinearLayout> 3 . In the MainActivity.java class, code the following: package net.learn2develop.Provider; import android.app.Activity; import android.os.Bundle; import android.app.ListActivity; import android.database.Cursor; import android.net.Uri; import android.provider.ContactsContract; import android.widget.SimpleCursorAdapter; public class MainActivity extends ListActivity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Uri allContacts = Uri.parse(“content://contacts/people”); Cursor c = managedQuery(allContacts, null, null, null, null); String[] columns = new String[] { ContactsContract.Contacts.DISPLAY_NAME, ContactsContract.Contacts._ID}; int[] views = new int[] {R.id.contactName, R.id.contactID}; SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.main, c, columns, views); this.setListAdapter(adapter); } }
- 263. Using a Content Provider ❘ 241 4 . Add the following statements in bold to the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Provider” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”7” /> <uses-permission android:name=”android.permission.READ_CONTACTS”> </uses-permission> </manifest> 5 . Launch an AVD and create a few contacts in the Android Emulator (see Figure 7-2). Figure 7-2 6 . Press F11 to debug the application on the Android Emulator. Figure 7-3 shows the activity displaying the list of contacts you just created.
- 264. 242 ❘ Chapter 7 Content Providers Figure 7-3 How It Works In this example, you retrieved all the contacts stored in the Contacts application and displayed them in the ListView. The managedQuery() method of the Activity class retrieves a managed cursor. A managed cursor handles all the work of unloading itself when the application pauses and requerying itself when the application restarts. The statement Cursor c = managedQuery(allContacts, null, null, null, null); is equivalent to Cursor c = getContentResolver().query(allContacts, null, null, null, null); startManagingCursor(c); //---allows the activity to manage the Cursor’s // lifecyle based on the activity’s lifecycle--- The getContentResolver() method returns a ContentResolver object, which helps to resolve a content URI with the appropriate content provider. The SimpleCursorAdapter object maps a cursor to TextViews (or ImageViews) defined in your XML file (main.xml). It maps the data (as represented by columns) to views (as represented by views): String[] columns = new String[] { ContactsContract.Contacts.DISPLAY_NAME, ContactsContract.Contacts._ID};
- 265. Using a Content Provider ❘ 243 int[]views=newint[]{R.id.contactName,R.id.contactID}; SimpleCursorAdapteradapter= newSimpleCursorAdapter(this,R.layout.main,c,columns,views); this.setListAdapter(adapter); Note that in order for your application to access the Contacts application, you need to have the READ_ CONTACTS permission in your AndroidManifest.xml fi le. predefined Query String constants Besides using the query URI, you can use a list of predefined query string constants in Android to specify the URI for the different data types. For example, besides using the query content://contacts/people, you can rewrite the following statement UriallContacts=Uri.parse(“content://contacts/people”); using one of the predefi ned constants in Android, as UriallContacts=ContactsContract.Contacts.CONTENT_URI; NOTE For Android 2.0 and later, to query the base Contacts records you need to use the ContactsContract.Contacts.CONTENT_URI URI. Some examples of predefi ned query string constants are as follows: ➤➤ Browser.BOOKMARKS_URI ➤➤ Browser.SEARCHES_URI ➤➤ CallLog.CONTENT_URI ➤➤ MediaStore.Images.Media.INTERNAL_CONTENT_URI ➤➤ MediaStore.Images.Media.EXTERNAL_CONTENT_URI ➤➤ Settings.CONTENT_URI If you want to retrieve the fi rst contact, specify the ID of that contact, like this: UrioneContact=Uri.parse(“content://contacts/people/1”); Alternatively, use the predefi ned constant together with the withAppendedId() method of the ContentUris class: importandroid.content.ContentUris; //... UrioneContact=ContentUris.withAppendedId( ContactsContract.Contacts.CONTENT_URI,1);
- 266. 244 ❘ Chapter 7 Content Providers Besides binding to a ListView, you can also print out the results using the Cursor object, as shown here: package net.learn2develop.Provider; import android.app.Activity; import android.os.Bundle; import android.app.ListActivity; import android.database.Cursor; import android.net.Uri; import android.provider.ContactsContract; import android.widget.SimpleCursorAdapter; import android.util.Log; public class MainActivity extends ListActivity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Uri allContacts = ContactsContract.Contacts.CONTENT_URI; Cursor c = managedQuery( allContacts, null, null, null, null); String[] columns = new String[] { ContactsContract.Contacts.DISPLAY_NAME, ContactsContract.Contacts._ID}; int[] views = new int[] {R.id.contactName, R.id.contactID}; SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.main, c, columns, views); this.setListAdapter(adapter); PrintContacts(c); } private void PrintContacts(Cursor c) { if (c.moveToFirst()) { do{ String contactID = c.getString(c.getColumnIndex( ContactsContract.Contacts._ID)); String contactDisplayName = c.getString(c.getColumnIndex( ContactsContract.Contacts.DISPLAY_NAME)); Log.v(“Content Providers”, contactID + “, “ + contactDisplayName); } while (c.moveToNext()); } } }
- 267. Using a Content Provider ❘ 245 NOTE If you are not familiar with how to view the LogCat window, refer to Appendix A for an quick tour of the Eclipse IDE. The PrintContacts() method will print out the following in the LogCat window: 12-1302:40:36.825:VERBOSE/ContentProviders(497): 1,Wei-MengLee 12-1302:40:36.825:VERBOSE/ContentProviders(497): 2,SallyJackson It prints out the ID and name of each contact stored in the Contacts application. In this case, you access the ContactsContract.Contacts._ID field to obtain the ID of a contact, and ContactsContract .Contacts.DISPLAY_NAME for the name of a contact. If you want to display the phone number of a contact, you need to query the content provider again, as the information is stored in another table: privatevoidPrintContacts(Cursorc) { if(c.moveToFirst()){ do{ StringcontactID=c.getString(c.getColumnIndex( ContactsContract.Contacts._ID)); StringcontactDisplayName= c.getString(c.getColumnIndex( ContactsContract.Contacts.DISPLAY_NAME)); Log.v(“ContentProviders”,contactID+“,“+ contactDisplayName); //---get phone number--- int hasPhone = c.getInt(c.getColumnIndex( ContactsContract.Contacts.HAS_PHONE_NUMBER)); Do if (hasPhone == 1) { Cursor phoneCursor = getContentResolver().query( ContactsContract.CommonDataKinds.Phone.CONTENT_URI, null, ContactsContract.CommonDataKinds.Phone.CONTACT_ID + “ = “ + contactID, null, null); while (phoneCursor.moveToNext()) { Log.v(“Content Providers”, phoneCursor.getString( phoneCursor.getColumnIndex( ContactsContract.CommonDataKinds.Phone.NUMBER))); } phoneCursor.close(); } }while(c.moveToNext()); } } }
- 268. 246 ❘ chApter 7 content ProviderS NOTE To access the phone number of a contact, you need to query against the URI stored in ContactsContract.CommonDataKinds.Phone.CONTENT_URI. In the preceding code snippet, you fi rst check whether a contact has a phone number using the ContactsContract.Contacts.HAS_PHONE_NUMBER field. If the contact has at least a phone number, you then query the content provider again based on the ID of the contact. Once the phone number(s) are retrieved, you then iterate through them and print out the numbers. You should see something like this: 12-1302:41:09.541:VERBOSE/ContentProviders(546): 1,Wei-MengLee 12-1302:41:09.541:VERBOSE/ContentProviders(546): 969-240-65 12-1302:41:09.541:VERBOSE/ContentProviders(546): 2,SallyJackson 12-1302:41:09.541:VERBOSE/ContentProviders(546): 345-668-43 projections The second parameter of the managedQuery() method controls how many columns are returned by the query; this parameter is known as the projection. Earlier, you specified null: Cursorc=managedQuery(allContacts, null,null,null,null); You can specify the exact columns to return by creating an array containing the name of the column to return, like this: String[]projection=newString[] {ContactsContract.Contacts._ID, ContactsContract.Contacts.DISPLAY_NAME, ContactsContract.Contacts.HAS_PHONE_NUMBER}; Cursorc=managedQuery(allContacts,projection, null,null,null); In the above case, the _ID, DISPLAY_NAME, and HAS_PHONE_NUMBER fields will be retrieved. Filtering The third and fourth parameters of the managedQuery() method enable you to specify a SQL WHERE clause to fi lter the result of the query. For example, the following statement retrieves only the people whose name ends with “Lee”: Cursorc=managedQuery(allContacts,projection, ContactsContract.Contacts.DISPLAY_NAME+“LIKE‘%Lee’”, null,null);
- 269. Creating Your Own Content Providers ❘ 247 Here, the third parameter contains a SQL statement containing the name to search for (“Lee”). You can also put the search string into the fourth argument of the method, like this: Cursor c = managedQuery(allContacts, projection, ContactsContract.Contacts.DISPLAY_NAME + “ LIKE ?”, new String[] {“%Lee”} , null); Sorting The fifth parameter of the managedQuery() method enables you to specify a SQL ORDER BY clause to sort the result of the query. For example, the following statement sorts the contact names in ascend- ing order: Cursor c = managedQuery( allContacts, projection, ContactsContract.Contacts.DISPLAY_NAME + “ LIKE ?”, new String[] {“%”} , ContactsContract.Contacts.DISPLAY_NAME + “ ASC”); To sort in descending order, use the DESC keyword: Cursor c = managedQuery( allContacts, projection, ContactsContract.Contacts.DISPLAY_NAME + “ LIKE ?”, new String[] {“%”} , ContactsContract.Contacts.DISPLAY_NAME + “ DESC”); Creating Your Own Content Providers Creating your own content provider in Android is pretty simple. All you need to do is extend the abstract ContentProvider class and override the various methods defined within it. In this section, you will learn how to create a simple content pro- vider that stores a list of books. For ease of illustration, the content provider stores the books in a database table containing three fields, as shown in Figure 7-4. Figure 7-4 The following Try It Out shows you the steps. Try It Out Creating Your Own Content Provider codefile ContentProviders.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it as ContentProviders.
- 270. 248 ❘ Chapter 7 Content Providers 2 . In the src folder of the project, add a new Java class file and name it BooksProvider.java (see Figure 7-5). Figure 7-5 3 . Populate the BooksProvider.java file as follows: package net.learn2develop.ContentProviders; import android.content.ContentProvider; import android.content.ContentUris; import android.content.ContentValues; import android.content.Context; import android.content.UriMatcher; import android.database.Cursor; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import android.database.sqlite.SQLiteQueryBuilder; import android.net.Uri; import android.text.TextUtils; import android.util.Log; public class BooksProvider extends ContentProvider { public static final String PROVIDER_NAME = “net.learn2develop.provider.Books”; public static final Uri CONTENT_URI = Uri.parse(“content://”+ PROVIDER_NAME + “/books”); public static final String _ID = “_id”; public static final String TITLE = “title”; public static final String ISBN = “isbn”; private static final int BOOKS = 1; private static final int BOOK_ID = 2; private static final UriMatcher uriMatcher; static{ uriMatcher = new UriMatcher(UriMatcher.NO_MATCH); uriMatcher.addURI(PROVIDER_NAME, “books”, BOOKS); uriMatcher.addURI(PROVIDER_NAME, “books/#”, BOOK_ID); } //---for database use--- private SQLiteDatabase booksDB;
- 271. Creating Your Own Content Providers ❘ 249 private static final String DATABASE_NAME = “Books”; private static final String DATABASE_TABLE = “titles”; private static final int DATABASE_VERSION = 1; private static final String DATABASE_CREATE = “create table “ + DATABASE_TABLE + “ (_id integer primary key autoincrement, “ + “title text not null, isbn text not null);”; private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(DATABASE_CREATE); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(“Content provider database”, “Upgrading database from version “ + oldVersion + “ to “ + newVersion + “, which will destroy all old data”); db.execSQL(“DROP TABLE IF EXISTS titles”); onCreate(db); } } @Override public int delete(Uri arg0, String arg1, String[] arg2) { // arg0 = uri // arg1 = selection // arg2 = selectionArgs int count=0; switch (uriMatcher.match(arg0)){ case BOOKS: count = booksDB.delete( DATABASE_TABLE, arg1, arg2); break; case BOOK_ID: String id = arg0.getPathSegments().get(1); count = booksDB.delete( DATABASE_TABLE, _ID + “ = “ + id + (!TextUtils.isEmpty(arg1) ? “ AND (“ + arg1 + ‘)’ : “”), arg2); break; default: throw new IllegalArgumentException(“Unknown URI “ + arg0);
- 272. 250 ❘ Chapter 7 Content Providers } getContext().getContentResolver().notifyChange(arg0, null); return count; } @Override public String getType(Uri uri) { switch (uriMatcher.match(uri)){ //---get all books--- case BOOKS: return “vnd.android.cursor.dir/vnd.learn2develop.books “; //---get a particular book--- case BOOK_ID: return “vnd.android.cursor.item/vnd.learn2develop.books “; default: throw new IllegalArgumentException(“Unsupported URI: “ + uri); } } @Override public Uri insert(Uri uri, ContentValues values) { //---add a new book--- long rowID = booksDB.insert( DATABASE_TABLE, “”, values); //---if added successfully--- if (rowID>0) { Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID); getContext().getContentResolver().notifyChange(_uri, null); return _uri; } throw new SQLException(“Failed to insert row into “ + uri); } @Override public boolean onCreate() { Context context = getContext(); DatabaseHelper dbHelper = new DatabaseHelper(context); booksDB = dbHelper.getWritableDatabase(); return (booksDB == null)? false:true; } @Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { SQLiteQueryBuilder sqlBuilder = new SQLiteQueryBuilder(); sqlBuilder.setTables(DATABASE_TABLE); if (uriMatcher.match(uri) == BOOK_ID) //---if getting a particular book--- sqlBuilder.appendWhere(
- 273. Creating Your Own Content Providers ❘ 251 _ID + “ = “ + uri.getPathSegments().get(1)); if (sortOrder==null || sortOrder==””) sortOrder = TITLE; Cursor c = sqlBuilder.query( booksDB, projection, selection, selectionArgs, null, null, sortOrder); //---register to watch a content URI for changes--- c.setNotificationUri(getContext().getContentResolver(), uri); return c; } @Override public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { int count = 0; switch (uriMatcher.match(uri)){ case BOOKS: count = booksDB.update( DATABASE_TABLE, values, selection, selectionArgs); break; case BOOK_ID: count = booksDB.update( DATABASE_TABLE, values, _ID + “ = “ + uri.getPathSegments().get(1) + (!TextUtils.isEmpty(selection) ? “ AND (“ + selection + ‘)’ : “”), selectionArgs); break; default: throw new IllegalArgumentException(“Unknown URI “ + uri); } getContext().getContentResolver().notifyChange(uri, null); return count; } } 4 . Add the following statements in bold to the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.ContentProviders” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”>
- 274. 252 ❘ Chapter 7 Content Providers <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> <provider android:name=”BooksProvider” android:authorities=”net.learn2develop.provider.Books” /> </application> <uses-sdk android:minSdkVersion=”9” /> </manifest> How It Works In this example, you first created a class named BooksProvider that extends the ContentProvider base class. The various methods to override in this class are as follows: ➤➤ getType() — Returns the MIME type of the data at the given URI ➤➤ onCreate() — Called when the provider is started ➤➤ query() — Receives a request from a client. The result is returned as a Cursor object. ➤➤ insert() — Inserts a new record into the content provider ➤➤ delete() — Deletes an existing record from the content provider ➤➤ update() — Updates an existing record from the content provider Within your content provider, you are free to choose how you want to store your data — a traditional file system, XML, a database, or even through Web services. For this example, you use the SQLite database approach that was discussed in the previous chapter. You then defined the following constants within the BooksProvider class: public static final String PROVIDER_NAME = “net.learn2develop.provider.Books”; public static final Uri CONTENT_URI = Uri.parse(“content://”+ PROVIDER_NAME + “/books”); public static final String _ID = “_id”; public static final String TITLE = “title”; public static final String ISBN = “isbn”; private static final int BOOKS = 1; private static final int BOOK_ID = 2; private static final UriMatcher uriMatcher; static{ uriMatcher = new UriMatcher(UriMatcher.NO_MATCH); uriMatcher.addURI(PROVIDER_NAME, “books”, BOOKS); uriMatcher.addURI(PROVIDER_NAME, “books/#”, BOOK_ID); }
- 275. Creating Your Own Content Providers ❘ 253 Observe in the preceding code that you use an UriMatcher object to parse the content URI that is passed to the content provider through a ContentResolver. For example, the following content URI represents a request for all books in the content provider: content://net.learn2develop.provider.Books/books The following represents a request for a particular book with _id 5: content://net.learn2develop.provider.MailingList/books/5 Your content provider uses a SQLite database to store the books. Note that you use the SQLiteOpenHelper helper class to help manage your database: private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(DATABASE_CREATE); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(“Content provider database”, “Upgrading database from version “ + oldVersion + “ to “ + newVersion + “, which will destroy all old data”); db.execSQL(“DROP TABLE IF EXISTS titles”); onCreate(db); } } Next, you override the getType() method to uniquely describe the data type for your content provider. Using the UriMatcher object, you return “vnd.android.cursor.item/vnd.learn2develop.books” for a single book, and “vnd.android.cursor.dir/vnd.learn2develop.books” for multiple books: @Override public String getType(Uri uri) { switch (uriMatcher.match(uri)){ //---get all books--- case BOOKS: return “vnd.android.cursor.dir/vnd.learn2develop.books “; //---get a particular book--- case BOOK_ID: return “vnd.android.cursor.item/vnd.learn2develop.books “; default: throw new IllegalArgumentException(“Unsupported URI: “ + uri); } }
- 276. 254 ❘ Chapter 7 Content Providers Next, you override the onCreate() method to open a connection to the database when the content provider is started: @Override public boolean onCreate() { Context context = getContext(); DatabaseHelper dbHelper = new DatabaseHelper(context); booksDB = dbHelper.getWritableDatabase(); return (booksDB == null)? false:true; } You override the query() method to allow clients to query for books: @Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { SQLiteQueryBuilder sqlBuilder = new SQLiteQueryBuilder(); sqlBuilder.setTables(DATABASE_TABLE); if (uriMatcher.match(uri) == BOOK_ID) //---if getting a particular book--- sqlBuilder.appendWhere( _ID + “ = “ + uri.getPathSegments().get(1)); if (sortOrder==null || sortOrder==””) sortOrder = TITLE; Cursor c = sqlBuilder.query( booksDB, projection, selection, selectionArgs, null, null, sortOrder); //---register to watch a content URI for changes--- c.setNotificationUri(getContext().getContentResolver(), uri); return c; } By default, the result of the query is sorted using the title field. The resulting query is returned as a Cursor object. To allow a new book to be inserted into the content provider, override the insert() method: @Override public Uri insert(Uri uri, ContentValues values) { //---add a new book--- long rowID = booksDB.insert( DATABASE_TABLE, “”, values); //---if added successfully--- if (rowID>0)
- 277. Creating Your Own Content Providers ❘ 255 { Uri _uri = ContentUris.withAppendedId(CONTENT_URI, rowID); getContext().getContentResolver().notifyChange(_uri, null); return _uri; } throw new SQLException(“Failed to insert row into “ + uri); } Once the record is inserted successfully, call the notifyChange() method of the ContentResolver. This will notify registered observers that a row was updated. To delete a book, override the delete() method: public int delete(Uri arg0, String arg1, String[] arg2) { // arg0 = uri // arg1 = selection // arg2 = selectionArgs int count=0; switch (uriMatcher.match(arg0)){ case BOOKS: count = booksDB.delete( DATABASE_TABLE, arg1, arg2); break; case BOOK_ID: String id = arg0.getPathSegments().get(1); count = booksDB.delete( DATABASE_TABLE, _ID + “ = “ + id + (!TextUtils.isEmpty(arg1) ? “ AND (“ + arg1 + ‘)’ : “”), arg2); break; default: throw new IllegalArgumentException(“Unknown URI “ + arg0); } getContext().getContentResolver().notifyChange(arg0, null); return count; } Likewise, call the notifyChange() method of the ContentResolver after the deletion. This will notify registered observers that a row was deleted. Finally, to update a book, override the update() method: @Override public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { int count = 0; switch (uriMatcher.match(uri)){ case BOOKS: count = booksDB.update( DATABASE_TABLE, values, selection, selectionArgs);
- 278. 256 ❘ Chapter 7 Content Providers break; case BOOK_ID: count = booksDB.update( DATABASE_TABLE, values, _ID + “ = “ + uri.getPathSegments().get(1) + (!TextUtils.isEmpty(selection) ? “ AND (“ + selection + ‘)’ : “”), selectionArgs); break; default: throw new IllegalArgumentException(“Unknown URI “ + uri); } getContext().getContentResolver().notifyChange(uri, null); return count; } } As with the insert() and delete() methods, you call the notifyChange() method of the ContentResolver after the update. This notifies registered observers that a row was updated. Finally, to register your content provider with Android, modify the AndroidManifest.xml file by adding the <provider> element. Using the Content Provider Now that you have built your new content provider, you can test it from within your Android appli- cation. The following Try It Out demonstrates how this can be done. Try It Out Using the Newly Created Content Provider 1 . Using the same project created in the previous section, add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”ISBN” /> <EditText android:id=”@+id/txtISBN” android:layout_height=”wrap_content” android:layout_width=”fill_parent” /> <TextView android:layout_width=”fill_parent” android:layout_height=”wrap_content”
- 279. Creating Your Own Content Providers ❘ 257 android:text=”Title” /> <EditText android:id=”@+id/txtTitle” android:layout_height=”wrap_content” android:layout_width=”fill_parent” /> <Button android:text=”Add title” android:id=”@+id/btnAdd” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> <Button android:text=”Retrieve titles” android:id=”@+id/btnRetrieve” android:layout_width=”fill_parent” android:layout_height=”wrap_content” /> </LinearLayout> 2 . In the MainActivity.java file, add the following statements in bold: package net.learn2develop.ContentProviders; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.Toast; import android.content.ContentValues; import android.database.Cursor; import android.net.Uri; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button btnAdd = (Button) findViewById(R.id.btnAdd); btnAdd.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //---add a book--- ContentValues values = new ContentValues(); values.put(BooksProvider.TITLE, ((EditText) findViewById(R.id.txtTitle)).getText().toString()); values.put(BooksProvider.ISBN, ((EditText) findViewById(R.id.txtISBN)).getText().toString()); Uri uri = getContentResolver().insert( BooksProvider.CONTENT_URI, values);
- 280. 258 ❘ Chapter 7 Content Providers Toast.makeText(getBaseContext(),uri.toString(), Toast.LENGTH_LONG).show(); } }); Button btnRetrieve = (Button) findViewById(R.id.btnRetrieve); btnRetrieve.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //---retrieve the titles--- Uri allTitles = Uri.parse( “content://net.learn2develop.provider.Books/books”); Cursor c = managedQuery(allTitles, null, null, null, “title desc”); if (c.moveToFirst()) { do{ Log.v(“ContentProviders”, c.getString(c.getColumnIndex( BooksProvider._ID)) + “, “ + c.getString(c.getColumnIndex( BooksProvider.TITLE)) + “, “ + c.getString(c.getColumnIndex( BooksProvider.ISBN))); } while (c.moveToNext()); } } }); } } 3 . Press F11 to debug the application on the Android Emulator. 4. Enter an ISBN and title for a book and click the Add title button. Figure 7-6 shows the Toast class displaying the URI of the book added to the content provider. To retrieve all the titles stored in the content provider, click the Retrieve titles button and observe the values printed in the Logcat win- dow of Eclipse. How It Works First, you modified the activity so that users can enter a book’s ISBN and title to add to the content pro- vider that you have just created. To add a book to the content provider, you create a new ContentValues object and then populate it with the various information about a book: //---add a book--- ContentValues values = new ContentValues(); values.put(BooksProvider.TITLE, ((EditText) findViewById(R.id.txtTitle)).getText().toString()); values.put(BooksProvider.ISBN, ((EditText) findViewById(R.id.txtISBN)).getText().toString()); Uri uri = getContentResolver().insert( BooksProvider.CONTENT_URI, values);
- 281. Creating Your Own Content Providers ❘ 259 Figure 7-6 Notice that because your content provider is in the same package, you can use the BooksProvider.TITLE and the BooksProvider.ISBN constants to refer to the “title” and “isbn” fields, respectively. If you were accessing this content provider from another package, then you would not be able to use these constants. In that case, you need to specify the field name directly, like this: ContentValues values = new ContentValues(); values.put(“title”, ((EditText) findViewById(R.id.txtTitle)).getText().toString()); values.put(“isbn”, ((EditText) findViewById(R.id.txtISBN)).getText().toString()); Uri uri = getContentResolver().insert( Uri.parse( “content://net.learn2develop.provider.Books/books”), values); Toast.makeText(getBaseContext(),uri.toString(), Toast.LENGTH_LONG).show(); Also note that for external packages you need to refer to the content URI using the fully qualified content URI: Uri.parse( “content://net.learn2develop.provider.Books/books”), To retrieve all the titles in the content provider, you used the following code snippets: Uri allTitles = Uri.parse( “content://net.learn2develop.provider.Books/books”);
- 282. 260 ❘ Chapter 7 Content Providers Cursor c = managedQuery(allTitles, null, null, null, “title desc”); if (c.moveToFirst()) { do{ Log.v(“ContentProviders”, c.getString(c.getColumnIndex( BooksProvider._ID)) + “, “ + c.getString(c.getColumnIndex( BooksProvider.TITLE)) + “, “ + c.getString(c.getColumnIndex( BooksProvider.ISBN))); } while (c.moveToNext()); } The preceding query will return the result sorted in descending order based on the title field. If you want to update a book’s detail, call the update() method with the content URI indicating the book’s ID: ContentValues editedValues = new ContentValues(); editedValues.put(BooksProvider.TITLE, “Android Tips and Tricks”); getContentResolver().update( Uri.parse( “content://net.learn2develop.provider.Books/books/2”), editedValues, null, null); To delete a book, use the delete() method with the content URI indicating the book’s ID: getContentResolver().delete( Uri.parse(“content://net.learn2develop.provider.Books/books/2”), null, null); To delete all books, simply omit the book’s ID in your content URI: getContentResolver().delete( Uri.parse(“content://net.learn2develop.provider.Books/books”), null, null); Summary In this chapter, you learned what content providers are and how to use some of the built-in con- tent providers in Android. In particular, you have seen how to use the Contacts content provider. Google’s decision to provide content providers enables applications to share data through a standard set of programming interfaces. In addition to the built-in content providers, you can also create your own custom content provider to share data with other packages.
- 283. Summary ❘ 261 Exercises 1 . Write the query to retrieve all contacts from the Contacts application that contain the word “jack.” 2 . Name the methods that you need to override in your own implementation of a content provider. 3. How do you register a content provider in your AndroidManifest.xml file? Answers can be found in Appendix C.
- 284. 262 ❘ Chapter 7 Content Providers ⊲⊲ What You Learned In This Chapter Topic Key Concepts Retrieving a managed cursor Use the managedQuery() method. Two ways to specify a query for a Use either a query URI or a predefined query string constant. content provider Retrieving the value of a column in Use the getColumnIndex() method. a content provider Query URI for accessing a contact’s ContactsContract.Contacts.CONTENT_URI name Query URI for accessing a contact’s ContactsContract.CommonDataKinds.Phone.CONTENT_URI phone number Creating your own content provider Create a class and extend the ContentProvider class.
- 285. 8 Messaging and networking WhAt you Will leArn in thiS chApter ➤➤ How to send SMS messages programmatically from within your application ➤➤ How to send SMS messages using the built-in Messaging application ➤➤ How to receive incoming SMS messages ➤➤ How to send e-mail messages from your application ➤➤ How to connect to the Web using HTTP ➤➤ How to consume Web services Once your basic Android application is up and running, the next interesting thing you can add to it is the capability to communicate with the outside world. You may want your application to send an SMS message to another phone when an event happens (such as when you reach a particular geographical location), or you may wish to access a Web service that provides cer- tain services (such as currency exchange, weather, etc.). In this chapter, you learn how to send and receive SMS messages programmatically from within your Android application. You will also learn how to use the HTTP protocol to talk to web servers so that you can download text and binary data. The last part of this chapter shows you how to parse XML files to extract the relevant parts of an XML file — a technique that is useful if you are accessing Web services. SmS meSSAging SMS messaging is one of the main killer applications on a mobile phone today — for some users as necessary as the phone itself. Any mobile phone you buy today should have at least SMS messaging capabilities, and nearly all users of any age know how to send and receive
- 286. 264 ❘ Chapter 8 Messaging and Networking such messages. Android comes with a built-in SMS application that enables you to send and receive SMS messages. However, in some cases you might want to integrate SMS capabilities into your own Android application. For example, you might want to write an application that automatically sends a SMS message at regular time intervals. For example, this would be useful if you wanted to track the location of your kids — simply give them an Android device that sends out an SMS message con- taining its geographical location every 30 minutes. Now you know if they really went to the library after school! (Of course, that would also mean you would have to pay the fees incurred in sending all those SMS messages…) This section describes how you can programmatically send and receive SMS messages in your Android applications. The good news for Android developers is that you don’t need a real device to test SMS messaging: The free Android Emulator provides that capability. Sending SMS Messages Programmatically You will first learn how to send SMS messages programmatically from within your application. Using this approach, your application can automatically send an SMS message to a recipient without user intervention. The following Try It Out shows you how. Try It Out S ending SMS Messages codefile SMS.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it as shown in Figure 8-1. Figure 8-1
- 287. SMS Messaging ❘ 265 2 . Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <Button android:id=”@+id/btnSendSMS” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Send SMS” /> </LinearLayout> 3 . In the AndroidManifest.xml file, add the following statements in bold: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.SMS” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”8” /> <uses-permission android:name=”android.permission.SEND_SMS”></uses-permission> </manifest> 4 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.SMS; import android.app.Activity; import android.os.Bundle; import android.app.PendingIntent; import android.content.Intent; import android.telephony.SmsManager; import android.view.View; import android.widget.Button; public class MainActivity extends Activity { Button btnSendSMS; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
- 288. 266 ❘ Chapter 8 Messaging and Networking setContentView(R.layout.main); btnSendSMS = (Button) findViewById(R.id.btnSendSMS); btnSendSMS.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { sendSMS(“5556”, “Hello my friends!”); } }); } //---sends an SMS message to another device--- private void sendSMS(String phoneNumber, String message) { SmsManager sms = SmsManager.getDefault(); sms.sendTextMessage(phoneNumber, null, message, null, null); } } 5 . Press F11 to debug the application on the Android Emulator. Using the Android SDK and AVD Manager, launch another AVD. 6. On the first Android Emulator, click the Send SMS button to send an SMS message to the second emulator. The left side of Figure 8-2 shows the SMS message received by the second emulator (note the notification bar at the top of the second emulator). Figure 8-2
- 289. SMS Messaging ❘ 267 How It Works Android uses a permissions-based policy whereby all the permissions needed by an application must be specified in the AndroidManifest.xml file. This ensures that when the application is installed, the user knows exactly which access permissions it requires. Because sending SMS messages incurs additional costs on the user’s end, indicating the SMS permissions in the AndroidManifest.xml file enables users to decide whether to allow the application to install or not. To send an SMS message programmatically, you use the SmsManager class. Unlike other classes, you do not directly instantiate this class; instead, you call the getDefault() static method to obtain a SmsManager object. You then send the SMS message using the sendTextMessage() method: private void sendSMS(String phoneNumber, String message) { SmsManager sms = SmsManager.getDefault(); sms.sendTextMessage(phoneNumber, null, message, null, null); } Following are the five arguments to the sendTextMessage() method: ➤➤ destinationAddress — Phone number of the recipient ➤➤ scAddress — Service center address; use null for default SMSC ➤➤ text — Content of the SMS message ➤➤ sentIntent — Pending intent to invoke when the message is sent (discussed in more detail in the next section) ➤➤ deliveryIntent — Pending intent to invoke when the message has been delivered (discussed in more detail in the next section) Do Getting Feedback after Sending the Message In the previous section, you learned how to programmatically send SMS messages using the SmsManager class; but how do you know that the message has been sent correctly? To do so, you can create two PendingIntent objects to monitor the status of the SMS message-sending process. These two PendingIntent objects are passed to the last two arguments of the sendTextMessage() method. The following code snippets show how you can monitor the status of the SMS message being sent: //---sends an SMS message to another device--- private void sendSMS(String phoneNumber, String message) { String SENT = “SMS_SENT”; String DELIVERED = “SMS_DELIVERED”; PendingIntent sentPI = PendingIntent.getBroadcast(this, 0, new Intent(SENT), 0); PendingIntent deliveredPI = PendingIntent.getBroadcast(this, 0,
- 290. 268 ❘ Chapter 8 Messaging and Networking new Intent(DELIVERED), 0); //---when the SMS has been sent--- registerReceiver(new BroadcastReceiver(){ @Override public void onReceive(Context arg0, Intent arg1) { switch (getResultCode()) { case Activity.RESULT_OK: Toast.makeText(getBaseContext(), “SMS sent”, Toast.LENGTH_SHORT).show(); break; case SmsManager.RESULT_ERROR_GENERIC_FAILURE: Toast.makeText(getBaseContext(), “Generic failure”, Toast.LENGTH_SHORT).show(); break; case SmsManager.RESULT_ERROR_NO_SERVICE: Toast.makeText(getBaseContext(), “No service”, Toast.LENGTH_SHORT).show(); break; case SmsManager.RESULT_ERROR_NULL_PDU: Toast.makeText(getBaseContext(), “Null PDU”, Toast.LENGTH_SHORT).show(); break; case SmsManager.RESULT_ERROR_RADIO_OFF: Toast.makeText(getBaseContext(), “Radio off”, Toast.LENGTH_SHORT).show(); break; } } }, new IntentFilter(SENT)); //---when the SMS has been delivered--- registerReceiver(new BroadcastReceiver(){ @Override public void onReceive(Context arg0, Intent arg1) { switch (getResultCode()) { case Activity.RESULT_OK: Toast.makeText(getBaseContext(), “SMS delivered”, Toast.LENGTH_SHORT).show(); break; case Activity.RESULT_CANCELED: Toast.makeText(getBaseContext(), “SMS not delivered”, Toast.LENGTH_SHORT).show(); break; } } }, new IntentFilter(DELIVERED)); SmsManager sms = SmsManager.getDefault(); sms.sendTextMessage(phoneNumber, null, message, sentPI, deliveredPI); }
- 291. SMS Messaging ❘ 269 Here, you created two PendingIntent objects. You then registered for two BroadcastReceivers. These two BroadcastReceivers listen for intents that match “SMS_SENT” and “SMS_DELIVERED” (which are fired by the OS when the message has been sent and delivered, respectively). Within each BroadcastReceiver you override the onReceive() method and get the current result code. The two PendingIntent objects are passed into the last two arguments of the sendTextMessage() method: sms.sendTextMessage(phoneNumber, null, message, sentPI, deliveredPI); In this case, whether a message has been sent correctly or failed to be delivered, you will be notified of its status via the two PendingIntent objects. Sending SMS Messages Using Intent Using the SmsManager class, you can send SMS messages from within your application without the need to involve the built-in Messaging application. However, sometimes it would be easier if you could simply invoke the built-in Messaging application and let it do all the work of sending the message. To activate the built-in Messaging application from within your application, you can use an Intent object together with the MIME type “vnd.android-dir/mms-sms” as shown by the following code snippet: /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); btnSendSMS = (Button) findViewById(R.id.btnSendSMS); btnSendSMS.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //sendSMS(“5556”, “Hello my friends!”); Intent i = new Intent(android.content.Intent.ACTION_VIEW); i.putExtra(“address”, “5556; 5558; 5560”); i.putExtra(“sms_body”, “Hello my friends!”); i.setType(“vnd.android-dir/mms-sms”); startActivity(i); } }); } This will invoke the Messaging application, as shown in Figure 8-3. Note that you can send your SMS to multiple recipients by simply separating each phone number with a semicolon (in the putExtra() method).
- 292. 270 ❘ chApter 8 meSSaGinG and networKinG Figure 8-3 NOTE If you use this method to invoke the Messaging application, there is no need to ask for the SMS_SEND permission in AndroidManifest.xml because your application is ultimately not the one sending the message. receiving SmS messages Besides sending SMS messages from your Android applications, you can also receive incoming SMS messages from within your application by using a BroadcastReceiver object. This is useful when you want your application to perform an action when a certain SMS message is received. For example, you might want to track the location of your phone in case it is lost or stolen. In this case, you can write an application that automatically listens for SMS messages containing some secret code. Once that message is received, you can then send an SMS message containing the location’s coordinates back to the sender. The following Try It Out shows how to programmatically listen for incoming SMS messages. try it out Receiving SMS Messages 1 . Using the same project created in the previous section, add the following statements in bold to the AndroidManifest.xml file: <?xmlversion=”1.0”encoding=”utf-8”?> <manifestxmlns:android=”http://schemas.android.com/apk/res/android”
- 293. SMS Messaging ❘ 271 package=”net.learn2develop.SMS” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> <receiver android:name=”.SMSReceiver”> <intent-filter> <action android:name= “android.provider.Telephony.SMS_RECEIVED” /> </intent-filter> </receiver> </application> <uses-sdk android:minSdkVersion=”8” /> <uses-permission android:name=”android.permission.SEND_SMS”></uses-permission> <uses-permission android:name=”android.permission.RECEIVE_SMS”> </uses-permission> </manifest> 2 . In the src folder of the project, add a new Class file to the package name and call it SMSReceiver.java (see Figure 8-4). 3. Code the SMSReceiver.java file as follows: package net.learn2develop.SMS; Figure 8-4 import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.os.Bundle; import android.telephony.SmsMessage; import android.widget.Toast; public class SMSReceiver extends BroadcastReceiver { @Override public void onReceive(Context context, Intent intent) { //---get the SMS message passed in--- Bundle bundle = intent.getExtras(); SmsMessage[] msgs = null; String str = “”; if (bundle != null) { //---retrieve the SMS message received--- Object[] pdus = (Object[]) bundle.get(“pdus”); msgs = new SmsMessage[pdus.length]; for (int i=0; i<msgs.length; i++){ msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]); str += “SMS from “ + msgs[i].getOriginatingAddress();
- 294. 272 ❘ Chapter 8 Messaging and Networking str += “ :”; str += msgs[i].getMessageBody().toString(); str += “n”; } //---display the new SMS message--- Toast.makeText(context, str, Toast.LENGTH_SHORT).show(); } } } 4 . Press F11 to debug the application on the Android Emulator. 5. Using the DDMS, send a message to the emulator. Your application should be able to receive the message and display it using the Toast class (see Figure 8-5). Figure 8-5 How It Works To listen for incoming SMS messages, you create a BroadcastReceiver class. The BroadcastReceiver class enables your application to receive intents sent by other applications using the sendBroadcast() method. Essentially, it enables your application to handle events raised by other applications. When an intent is received, the onReceive() method is called; hence, you need to override this. When an incoming SMS message is received, the onReceive() method is fired. The SMS message is contained in the Intent object (intent; the second parameter in the onReceive() method) via a Bundle object. The messages are stored in an Object array in the PDU format. To extract each message, you use the static createFromPdu() method from the SmsMessage class. The SMS message is then displayed using the Toast class. The phone number of the sender is obtained via the getOriginatingAddress()
- 295. SMS Messaging ❘ 273 method, so if you need to send an autoreply to the sender, this is the method to obtain the sender’s phone number. One interesting characteristic of the BroadcastReceiver is that you can continue to listen for incoming SMS messages even if the application is not running; as long as the application is installed on the device, any incoming SMS messages will be received by the application. Updating an Activity from a BroadcastReceiver The previous section described how you can use a BroadcastReceiver class to listen for incoming SMS messages and then use the Toast class to display the received SMS message. Often, you’ll want to send the SMS message back to the main activity of your application. For example, you might wish to display the message in a TextView. The following Try It Out demonstrates how you can do this. Try It Out C reating a View-Based Application Project 1 . Using the same project created in the previous section, add the following lines in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <Button android:id=”@+id/btnSendSMS” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Send SMS” /> <TextView android:id=”@+id/textView1” android:layout_width=”wrap_content” android:layout_height=”wrap_content” /> </LinearLayout> 2 . Add the following statements in bold to the SMSReceiver.java file: package net.learn2develop.SMS; import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.os.Bundle; import android.telephony.SmsMessage; import android.widget.Toast; public class SMSReceiver extends BroadcastReceiver
- 296. 274 ❘ Chapter 8 Messaging and Networking { @Override public void onReceive(Context context, Intent intent) { //---get the SMS message passed in--- Bundle bundle = intent.getExtras(); SmsMessage[] msgs = null; String str = “”; if (bundle != null) { //---retrieve the SMS message received--- Object[] pdus = (Object[]) bundle.get(“pdus”); msgs = new SmsMessage[pdus.length]; for (int i=0; i<msgs.length; i++){ msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]); str += “SMS from “ + msgs[i].getOriginatingAddress(); str += “ :”; str += msgs[i].getMessageBody().toString(); str += “n”; } //---display the new SMS message--- Toast.makeText(context, str, Toast.LENGTH_SHORT).show(); //---send a broadcast intent to update the SMS received in the activity--- Intent broadcastIntent = new Intent(); broadcastIntent.setAction(“SMS_RECEIVED_ACTION”); broadcastIntent.putExtra(“sms”, str); context.sendBroadcast(broadcastIntent); } } } 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.SMS; import android.app.Activity; import android.os.Bundle; import android.app.PendingIntent; import android.content.Context; import android.content.Intent; import android.telephony.SmsManager; import android.view.View; import android.widget.Button; import android.widget.Toast; import android.content.BroadcastReceiver; import android.content.IntentFilter; import android.widget.TextView; public class MainActivity extends Activity { Button btnSendSMS; IntentFilter intentFilter; private BroadcastReceiver intentReceiver = new BroadcastReceiver() {
- 297. SMS Messaging ❘ 275 @Override public void onReceive(Context context, Intent intent) { //---display the SMS received in the TextView--- TextView SMSes = (TextView) findViewById(R.id.textView1); SMSes.setText(intent.getExtras().getString(“sms”)); } }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---intent to filter for SMS messages received--- intentFilter = new IntentFilter(); intentFilter.addAction(“SMS_RECEIVED_ACTION”); btnSendSMS = (Button) findViewById(R.id.btnSendSMS); btnSendSMS.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //sendSMS(“5554”, “Hello my friends!”); Intent i = new Intent(android.content.Intent.ACTION_VIEW); i.putExtra(“address”, “5556; 5558; 5560”); i.putExtra(“sms_body”, “Hello my friends!”); i.setType(“vnd.android-dir/mms-sms”); startActivity(i); } }); } @Override protected void onResume() { //---register the receiver--- registerReceiver(intentReceiver, intentFilter); super.onResume(); } @Override protected void onPause() { //---unregister the receiver--- unregisterReceiver(intentReceiver); super.onPause(); } //---sends an SMS message to another device--- private void sendSMS(String phoneNumber, String message) { //... } }
- 298. 276 ❘ Chapter 8 Messaging and Networking 4 . Press F11 to debug the application on the Android Emulator. Using the DDMS, send an SMS message to the emulator. Figure 8-6 shows the Toast class displaying the message received, and the TextView showing the message received. Figure 8-6 How It Works You first added a TextView to your activity so that it can be used to display the received SMS message. Next, you modified the SMSReceiver class so that when it receives an SMS message, it will broadcast another Intent object so that any applications listening for this intent can be notified (which we will implement in the activity next). The SMS received is also sent out via this intent: //---send a broadcast intent to update the SMS received in the activity--- Intent broadcastIntent = new Intent(); broadcastIntent.setAction(“SMS_RECEIVED_ACTION”); broadcastIntent.putExtra(“sms”, str); context.sendBroadcast(broadcastIntent); Next, in your activity you created a BroadcastReceiver object to listen for broadcast intents: private BroadcastReceiver intentReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { //---display the SMS received in the TextView--- TextView SMSes = (TextView) findViewById(R.id.textView1); SMSes.setText(intent.getExtras().getString(“sms”)); } };
- 299. SMS Messaging ❘ 277 When a broadcast intent is received, you update the SMS message in the TextView. You need to create an IntentFilter object so that you can listen for a particular intent. In this case, the intent is “SMS_RECEIVED_ACTION”: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---intent to filter for SMS messages received--- intentFilter = new IntentFilter(); intentFilter.addAction(“SMS_RECEIVED_ACTION”); //... } Finally, you register the BroadcastReceiver in the activity’s onResume() event and unregister it in the onPause() event: @Override protected void onResume() { //---register the receiver--- registerReceiver(intentReceiver, intentFilter); super.onResume(); } @Override protected void onPause() { //---unregister the receiver--- unregisterReceiver(intentReceiver); super.onPause(); } This means that the TextView will display the SMS message only when the message is received while the activity is visible on the screen. If the SMS message is received when the activity is not in the foreground, the TextView will not be updated. Invoking an Activity from a BroadcastReceiver The previous example shows how you can pass the SMS message received to be displayed in the activ- ity. However, in many situations your activity may be in the background when the SMS message is received. In this case, it would be useful to be able to bring the activity to the foreground when a mes- sage is received. The following Try It Out shows you how. Try It Out Invoking an Activity 1 . Using the same project created in the previous section, add the following lines in bold to the MainActivity.java file: /** Called when the activity is first created. */ @Override
- 300. 278 ❘ Chapter 8 Messaging and Networking public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---intent to filter for SMS messages received--- intentFilter = new IntentFilter(); intentFilter.addAction(“SMS_RECEIVED_ACTION”); //---register the receiver--- registerReceiver(intentReceiver, intentFilter); btnSendSMS = (Button) findViewById(R.id.btnSendSMS); btnSendSMS.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //sendSMS(“5554”, “Hello my friends!”); Intent i = new Intent(android.content.Intent.ACTION_VIEW); i.putExtra(“address”, “5556; 5558; 5560”); i.putExtra(“sms_body”, “Hello my friends!”); i.setType(“vnd.android-dir/mms-sms”); startActivity(i); } }); } @Override protected void onResume() { //---register the receiver--- //registerReceiver(intentReceiver, intentFilter); super.onResume(); } @Override protected void onPause() { //---unregister the receiver--- //unregisterReceiver(intentReceiver); super.onPause(); } @Override protected void onDestroy() { //---unregister the receiver--- unregisterReceiver(intentReceiver); super.onPause(); } 2 . Add the following statements in bold to the SMSReceiver.java file: @Override public void onReceive(Context context, Intent intent) {
- 301. SMS Messaging ❘ 279 //---get the SMS message passed in--- Bundle bundle = intent.getExtras(); SmsMessage[] msgs = null; String str = “”; if (bundle != null) { //---retrieve the SMS message received--- Object[] pdus = (Object[]) bundle.get(“pdus”); msgs = new SmsMessage[pdus.length]; for (int i=0; i<msgs.length; i++){ msgs[i] = SmsMessage.createFromPdu((byte[])pdus[i]); str += “SMS from “ + msgs[i].getOriginatingAddress(); str += “ :”; str += msgs[i].getMessageBody().toString(); str += “n”; } //---display the new SMS message--- Toast.makeText(context, str, Toast.LENGTH_SHORT).show(); //---launch the MainActivity--- Intent mainActivityIntent = new Intent(context, MainActivity.class); mainActivityIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); context.startActivity(mainActivityIntent); //---send a broadcast to update the SMS received in the activity--- Intent broadcastIntent = new Intent(); broadcastIntent.setAction(“SMS_RECEIVED_ACTION”); broadcastIntent.putExtra(“sms”, str); context.sendBroadcast(broadcastIntent); } } 3 . Modify the main.xml file as follows: <activity android:name=”.MainActivity” android:label=”@string/app_name” android:launchMode=”singleTask” > <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> 4 . Press F11 to debug the application on the Android Emulator. When the MainActivity is shown, click the Home button to send the activity to the background. 5. Use the DDMS to send an SMS message to the emulator again. This time, note that the activity will be brought to the foreground, displaying the SMS message received. How It Works In the MainActivity class, you first register the BroadcastReceiver in the activity’s onCreate() event, instead of the onResume() event; and instead of unregistering it in the onPause() event, you now unregister
- 302. 280 ❘ Chapter 8 Messaging and Networking it in the onDestroy() event. This ensures that even if the activity is in the background, it will still be able to listen for the broadcast intent. Next, you modify the onReceive() event in the SMSReceiver class by using an intent to bring the activ- ity to the foreground before broadcasting another intent: //---launch the MainActivity--- Intent mainActivityIntent = new Intent(context, MainActivity.class); mainActivityIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); context.startActivity(mainActivityIntent); //---send a broadcast to update the SMS received in the activity--- Intent broadcastIntent = new Intent(); broadcastIntent.setAction(“SMS_RECEIVED_ACTION”); broadcastIntent.putExtra(“sms”, str); context.sendBroadcast(broadcastIntent); The startActivity() method launches the activity and brings it to the foreground. Note that you need to set the Intent.FLAG_ACTIVITY_NEW_TASK flag because calling startActivity() from outside of an activity context requires the FLAG_ACTIVITY_NEW_TASK flag. You also need to set the launchMode attribute of the <activity> element in the AndroidManifest.xml file to singleTask: <activity android:name=”.MainActivity” android:label=”@string/app_name” android:launchMode=”singleTask” > If you don’t set this, multiple instances of the activity will be launched as your application receives SMS messages. Note that in this example, when the activity is in the background (such as when you click the Home button to show the home screen), the activity is brought to the foreground and its TextView is updated with the SMS received. However, if the activity was killed (such as when you click the Back button to destroy it), the activity is launched again but the TextView is not updated. Caveats and Warnings While the ability to send and receive SMS messages makes Android a very compelling platform for developing sophisticated applications, this flexibility comes with a price. A seemingly innocent application may send SMS messages behind the scene without the user knowing, as demonstrated by a recent case of an SMS-based Trojan Android application (http://forum.vodafone.co.nz/topic/ 5719-android-sms-trojan-warning/). Claiming to be a media player, once installed, the application sends SMS messages to a premium number, resulting in huge phone bills for the user. While the user needs to explicitly give permission to your application, the request for permission is only shown at installation time. Figure 8-7 shows the request for permission that appears when you
- 303. Sending E‑Mail ❘ 281 try to install the application (as an APK file; Chapter 11 discusses packaging your Android applica- tions in more detail) on the emulator (same as on a real device). If the user clicks the Install button, he or she is considered to have given permission to allow the application to send and receive SMS messages. This is dangerous, as after the application is installed it can send and receive SMS mes- sages without ever prompting the user again. Figure 8-7 In addition to this, the application can also “sniff” for incoming SMS messages. For example, based on the techniques you learned from the previous section, you can easily write an application that checks for certain keywords in the SMS message. When an SMS message contains the keyword you are looking for, you can then use the Location Manager (discussed in Chapter 9) to obtain your geo- graphical location and then send the coordinates back to the sender of the SMS message. The sender could then easily track your location. All these tasks can be done easily without the user knowing it! That said, users should try to avoid installing Android applications that come from dubious sources, such as from unknown websites, strangers, etc. Sending E‑Mail Like SMS messaging, Android also supports e‑mail. The Gmail/Email application on Android enables you to configure an e‑mail account using POP3 or IMAP. Besides sending and receiving e‑mails using the Gmail/Email application, you can also send e‑mail messages programmatically from within your Android application. The following Try It Out shows you how.
- 304. 282 ❘ Chapter 8 Messaging and Networking Try It Out S ending E‑mail Programmatically codefile Emails.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it Emails. 2 . Add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <Button android:id=”@+id/btnSendEmail” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Send Email” /> </LinearLayout> 3 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Email; import android.app.Activity; import android.os.Bundle; import android.content.Intent; import android.net.Uri; import android.view.View; import android.widget.Button; public class MainActivity extends Activity { Button btnSendEmail; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); btnSendEmail = (Button) findViewById(R.id.btnSendEmail); btnSendEmail.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { String[] to = {“[email protected]”, “[email protected]”}; String[] cc = {“[email protected]”}; sendEmail(to, cc, “Hello”, “Hello my friends!”); } });
- 305. Sending E‑Mail ❘ 283 } //---sends an SMS message to another device--- private void sendEmail(String[] emailAddresses, String[] carbonCopies, String subject, String message) { Intent emailIntent = new Intent(Intent.ACTION_SEND); emailIntent.setData(Uri.parse(“mailto:”)); String[] to = emailAddresses; String[] cc = carbonCopies; emailIntent.putExtra(Intent.EXTRA_EMAIL, to); emailIntent.putExtra(Intent.EXTRA_CC, cc); emailIntent.putExtra(Intent.EXTRA_SUBJECT, subject); emailIntent.putExtra(Intent.EXTRA_TEXT, message); emailIntent.setType(“message/rfc822”); startActivity(Intent.createChooser(emailIntent, “Email”)); } } 4 . Press F11 to test the application on a real Android device. Click the Send Email button and you should see the Email application launched in your device, as shown in Figure 8-8. Figure 8-8 How It Works In this example, you are launching the built-in Email application to send an e‑mail message. To do so, you use an Intent object and set the various parameters using the setData(), putExtra(), and setType() methods: Intent emailIntent = new Intent(Intent.ACTION_SEND); emailIntent.setData(Uri.parse(“mailto:”)); String[] to = emailAddresses; String[] cc = carbonCopies; emailIntent.putExtra(Intent.EXTRA_EMAIL, to); emailIntent.putExtra(Intent.EXTRA_CC, cc); emailIntent.putExtra(Intent.EXTRA_SUBJECT, subject); emailIntent.putExtra(Intent.EXTRA_TEXT, message); emailIntent.setType(“message/rfc822”); startActivity(Intent.createChooser(emailIntent, “Email”));
- 306. 284 ❘ Chapter 8 Messaging and Networking Networking The previous sections covered how to get connected to the outside world using SMS and e‑mail. Another way to achieve that is to use the HTTP protocol. Using the HTTP protocol, you can perform a wide vari- ety of tasks, such as downloading web pages from a web server, downloading binary data, and so on. The following Try It Out creates an Android project so that you can use the HTTP protocol to con- nect to the Web to download all sorts of data. Try It Out C reating the Project codefile Networking.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it Networking. 2 . Add the following statement in bold to the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Networking” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”8” /> <uses-permission android:name=”android.permission.INTERNET”></uses-permission> </manifest> 3 . Import the following namespaces in the MainActivity.java file: package net.learn2develop.Networking; import android.app.Activity; import android.os.Bundle; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL; import java.net.URLConnection; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.widget.ImageView; import android.widget.Toast; import javax.xml.parsers.DocumentBuilder;
- 307. Networking ❘ 285 import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.parsers.ParserConfigurationException; import org.w3c.dom.Document; import org.w3c.dom.Element; import org.w3c.dom.Node; import org.w3c.dom.NodeList; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } } 4 . Define the OpenHttpConnection() method in the MainActivity.java file: public class MainActivity extends Activity { private InputStream OpenHttpConnection(String urlString) throws IOException { InputStream in = null; int response = -1; URL url = new URL(urlString); URLConnection conn = url.openConnection(); if (!(conn instanceof HttpURLConnection)) throw new IOException(“Not an HTTP connection”); try{ HttpURLConnection httpConn = (HttpURLConnection) conn; httpConn.setAllowUserInteraction(false); httpConn.setInstanceFollowRedirects(true); httpConn.setRequestMethod(“GET”); httpConn.connect(); response = httpConn.getResponseCode(); if (response == HttpURLConnection.HTTP_OK) { in = httpConn.getInputStream(); } } catch (Exception ex) { throw new IOException(“Error connecting”); } return in; } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } }
- 308. 286 ❘ Chapter 8 Messaging and Networking How It Works Because you are using the HTTP protocol to connect to the Web, your application needs the INTERNET permission; hence, the first thing you do is add the permission in the AndroidManifest.xml file. You then define the OpenHttpConnection() method, which takes a URL string and returns an InputStream object. Using an InputStream object, you can download the data by reading bytes from the stream object. In this method, you made use of the HttpURLConnection object to open an HTTP connection with a remote URL. You set all the various properties of the connection, such as the request method, and so on: HttpURLConnection httpConn = (HttpURLConnection) conn; httpConn.setAllowUserInteraction(false); httpConn.setInstanceFollowRedirects(true); httpConn.setRequestMethod(“GET”); After you try to establish a connection with the server, you get the HTTP response code from it. If the connection is established (via the response code HTTP_OK), then you proceed to get an InputStream object from the connection: httpConn.connect(); response = httpConn.getResponseCode(); if (response == HttpURLConnection.HTTP_OK) { in = httpConn.getInputStream(); } Using the InputStream object, you can then start to download the data from the server. Downloading Binary Data One of the common tasks you need to perform is downloading binary data from the Web. For example, you may want to download an image from a server so that you can display it in your application. The following Try It Out shows how this is done. Try It Out C reating the Project 1 . Using the same project created earlier, add the following statements in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <ImageView android:id=”@+id/img” android:layout_width=”wrap_content” android:layout_height=”wrap_content” android:layout_gravity=”center” /> </LinearLayout>
- 309. Networking ❘ 287 2 . Add the following statements in bold to the MainActivity.java file: public class MainActivity extends Activity { ImageView img; private InputStream OpenHttpConnection(String urlString) throws IOException { //... } private Bitmap DownloadImage(String URL) { Bitmap bitmap = null; InputStream in = null; try { in = OpenHttpConnection(URL); bitmap = BitmapFactory.decodeStream(in); in.close(); } catch (IOException e1) { Toast.makeText(this, e1.getLocalizedMessage(), Toast.LENGTH_LONG).show(); e1.printStackTrace(); } return bitmap; } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---download an image--- Bitmap bitmap = DownloadImage( “http://www.streetcar.org/mim/cable/images/cable-01.jpg”); img = (ImageView) findViewById(R.id.img); img.setImageBitmap(bitmap); } } 3 . Press F11 to debug the application on the Android Emulator. Figure 8-9 shows the image down- loaded from the Web and then displayed in the ImageView. How It Works The DownloadImage() method takes the URL of the image to download and then opens the connection to the server using the OpenHttpConnection() method that you have defined earlier. Using the InputStream object returned by the connection, the decodeStream() method from the BitmapFactory class is used to download and decode the data into a Bitmap object. The DownloadImage() method returns a Bitmap object.
- 310. 288 ❘ chApter 8 meSSaGinG and networKinG Figure 8-9 The image is then displayed using an ImageView view. reFerring to locAlhoSt From your emulAtor When working with the Android Emulator, you may frequently need to access data hosted on the local web server using localhost. For example, your own Web services is likely to be hosted on your local computer during development time and you want to test it on the same development machine you use to write your Android applica- tions. In such cases, you should use the special IP address of 10.0.2.2 (not 127.0.0.1) to refer to the host computer’s loopback interface. From the Android Emulator’s per- spective, localhost (127.0.0.1) refers to its own loopback interface. downloading text Files Besides downloading binary data, you can also download plain-text fi les. For example, you might be writing an RSS Reader application and hence need to download RSS XML feeds for processing. The following Try It Out shows how you can download a plain-text fi le in your application.
- 311. Networking ❘ 289 Try It Out D ownloading Plain-Text Files 1 . Using the same project created earlier, add the following statements in bold to the MainActivity .java file: public class MainActivity extends Activity { ImageView img; private InputStream OpenHttpConnection(String urlString) throws IOException { //... } private Bitmap DownloadImage(String URL) { //... } private String DownloadText(String URL) { int BUFFER_SIZE = 2000; InputStream in = null; try { in = OpenHttpConnection(URL); } catch (IOException e1) { Toast.makeText(this, e1.getLocalizedMessage(), Toast.LENGTH_LONG).show(); e1.printStackTrace(); return “”; } Do InputStreamReader isr = new InputStreamReader(in); int charRead; String str = “”; char[] inputBuffer = new char[BUFFER_SIZE]; try { while ((charRead = isr.read(inputBuffer))>0) { //---convert the chars to a String--- String readString = String.copyValueOf(inputBuffer, 0, charRead); str += readString; inputBuffer = new char[BUFFER_SIZE]; } in.close(); } catch (IOException e) { Toast.makeText(this, e.getLocalizedMessage(), Toast.LENGTH_LONG).show(); e.printStackTrace();
- 312. 290 ❘ Chapter 8 Messaging and Networking return “”; } return str; } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---download an image--- Bitmap bitmap = DownloadImage( “http://www.streetcar.org/mim/cable/images/cable-01.jpg”); img = (ImageView) findViewById(R.id.img); img.setImageBitmap(bitmap); //---download an RSS feed--- String str = DownloadText( “http://www.appleinsider.com/appleinsider.rss”); Toast.makeText(getBaseContext(), str, Toast.LENGTH_SHORT).show(); } } 2 . Press F11 to debug the application on the Android Emulator. Figure 8-10 shows the RSS feed downloaded and displayed using the Toast class. Figure 8-10
- 313. Networking ❘ 291 How It Works The DownloadText() method takes an URL of the text file to download and then returns the string of the text file downloaded. It basically opens an HTTP connection to the server and then uses an InputStreamReader object to read each character from the stream and save it in a String object. Accessing Web Services So far you have seen how to download images and text from the Web. The previous section showed how to download an RSS feed from a server. Very often, you need to download XML files and parse the contents (a good example of this is consuming Web services). Therefore, in this section you learn how to connect to a Web service using the HTTP GET method. Once the Web service returns a result in XML, you will extract the relevant parts and display its content using the Toast class. For this example, the web method you will be using is from http://services.aonaware.com/ DictService/DictService.asmx?op=Define. This web method is from a Dictionary Web service that returns the definitions of a given word. The web method takes a request in the following format: GET /DictService/DictService.asmx/Define?word=string HTTP/1.1 Host: services.aonaware.com HTTP/1.1 200 OK Content-Type: text/xml; charset=utf-8 Content-Length: length It returns a response in the following format: <?xml version=”1.0” encoding=”utf-8”?> <WordDefinition xmlns=”http://services.aonaware.com/webservices/”> <Word>string</Word> <Definitions> <Definition> <Word>string</Word> <Dictionary> <Id>string</Id> <Name>string</Name> </Dictionary> <WordDefinition>string</WordDefinition> </Definition> <Definition> <Word>string</Word> <Dictionary> <Id>string</Id> <Name>string</Name> </Dictionary> <WordDefinition>string</WordDefinition> </Definition> </Definitions> </WordDefinition>
- 314. 292 ❘ Chapter 8 Messaging and Networking Hence, to obtain the definition of a word, you need to establish an HTTP connection to the web method and then parse the XML result that is returned. The following Try It Out shows you how. Try It Out C onsuming Web Services 1 . Using the same project created earlier, add the following statements in bold to the MainActivity .java file: public class MainActivity extends Activity { ImageView img; private InputStream OpenHttpConnection(String urlString) throws IOException { //... } private Bitmap DownloadImage(String URL) { //... } private String DownloadText(String URL) { //... } private void WordDefinition(String word) { InputStream in = null; try { in = OpenHttpConnection( “http://services.aonaware.com/DictService/DictService.asmx/Define?word=” + word); Document doc = null; DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db; try { db = dbf.newDocumentBuilder(); doc = db.parse(in); } catch (ParserConfigurationException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } doc.getDocumentElement().normalize(); //---retrieve all the <Definition> nodes--- NodeList itemNodes = doc.getElementsByTagName(“Definition”); String strDefinition = “”; for (int i = 0; i < definitionElements.getLength(); i++) {
- 315. Networking ❘ 293 Node itemNode = definitionElements.item(i); if (itemNode.getNodeType() == Node.ELEMENT_NODE) { //---convert the Node into an Element--- Element definitionElement = (Element) itemNode; //---get all the <WordDefinition> elements under // the <Definition> element--- NodeList wordDefinitionElements = (definitionElement).getElementsByTagName( “WordDefinition”); strDefinition = “”; for (int j = 0; j < wordDefinitionElements.getLength(); j++) { //---convert a <WordDefinition> Node into an Element--- Element wordDefinitionElement = (Element) wordDefinitionElements.item(j); //---get all the child nodes under the // <WordDefinition> element--- NodeList textNodes = ((Node) wordDefinitionElement).getChildNodes(); strDefinition += ((Node) textNodes.item(0)).getNodeValue() + “. “; } //---display the title--- Toast.makeText(getBaseContext(),strDefinition, Toast.LENGTH_SHORT).show(); } } } catch (IOException e1) { Toast.makeText(this, e1.getLocalizedMessage(), Toast.LENGTH_LONG).show(); e1.printStackTrace(); } } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---download an image--- Bitmap bitmap = DownloadImage( “http://www.streetcar.org/mim/cable/images/cable-01.jpg”); img = (ImageView) findViewById(R.id.img); img.setImageBitmap(bitmap); //---download an RSS feed--- String str = DownloadText(
- 316. 294 ❘ Chapter 8 Messaging and Networking “http://www.appleinsider.com/appleinsider.rss”); Toast.makeText(getBaseContext(), str, Toast.LENGTH_SHORT).show(); //---access a Web service using GET--- WordDefinition(“Apple”); } } 2 . Press F11 to debug the application on the Android Emulator. Figure 8-11 shows the result of the Web service call being parsed and then displayed using the Toast class. Figure 8-11 How It Works The WordDefinition() method first opens an HTTP connection to the Web service, passing in the word that you are interested in: in = OpenHttpConnection( “http://services.aonaware.com/DictService/DictService.asmx/Define?word=” + word); It then uses the DocumentBuilderFactory and DocumentBuilder objects to obtain a Document (DOM) object from an XML file (which is the XML result returned by the Web service): Document doc = null; DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db; try {
- 317. Networking ❘ 295 db = dbf.newDocumentBuilder(); doc = db.parse(in); } catch (ParserConfigurationException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } doc.getDocumentElement().normalize(); Once the Document object is obtained, you will find all the elements with the <Definition> tag: //---retrieve all the <Definition> nodes--- NodeList itemNodes = doc.getElementsByTagName(“Definition”); Figure 8-12 shows the structure of the XML document returned by the Web service. Figure 8-12 As the definition of a word is contained within the <WordDefinition> element, you then proceed to extract all the definitions: String strDefinition = “”; for (int i = 0; i < definitionElements.getLength(); i++) { Node itemNode = definitionElements.item(i); if (itemNode.getNodeType() == Node.ELEMENT_NODE) { //---convert the Node into an Element--- Element definitionElement = (Element) itemNode; //---get all the <WordDefinition> elements under // the <Definition> element--- NodeList wordDefinitionElements = (definitionElement).getElementsByTagName( “WordDefinition”); strDefinition = “”; for (int j = 0; j < wordDefinitionElements.getLength(); j++) { //---convert a <WordDefinition> Node into an Element---
- 318. 296 ❘ Chapter 8 Messaging and Networking Element wordDefinitionElement = (Element) wordDefinitionElements.item(j); //---get all the child nodes under the // <WordDefinition> element--- NodeList textNodes = ((Node) wordDefinitionElement).getChildNodes(); //---get the first node, which contains the text--- strDefinition += ((Node) textNodes.item(0)).getNodeValue() + “. “; } //---display the title--- Toast.makeText(getBaseContext(),strDefinition, Toast.LENGTH_SHORT).show(); } } } catch (IOException e1) { Toast.makeText(this, e1.getLocalizedMessage(), Toast.LENGTH_LONG).show(); e1.printStackTrace(); } The above loops through all the <Definition> elements and then for each <Definition> element it looks for a child element named <WordDefinition>. The text content of the <WordDefinition> element contains the definition of a word. The Toast class displays each word definition that is retrieved. Performing Asynchronous Calls So far, all the connections made in the previous few sections are all synchronous – that is, the con- nection to a server will not return until the data is received. In real life, this presents some problems due to network connections being inherently slow. When you connect to a server to download some data, the user interface of your application remains frozen until a response is obtained. In most cases, this is not acceptable. Hence, you need to ensure that the connection to the server is made in an asyn- chronous fashion. The easiest way to connect to the server asynchronously is to use the AsyncTask class available in the Android SDK. Using AsyncTask enables you to perform background tasks in a separate thread and then return the result in a UI thread. Using this class enables you to perform background operations without needing to handle complex threading issues. Using the previous example of downloading an image from the server and then displaying the image in an ImageView, you could wrap the code in an instance of the AsyncTask class, as shown below: public class MainActivity extends Activity { ImageView img; private class BackgroundTask extends AsyncTask <String, Void, Bitmap> { protected Bitmap doInBackground(String... url) {
- 319. Summary ❘ 297 //---download an image--- Bitmap bitmap = DownloadImage(url[0]); return bitmap; } protected void onPostExecute(Bitmap bitmap) { ImageView img = (ImageView) findViewById(R.id.img); img.setImageBitmap(bitmap); } } privateInputStreamOpenHttpConnection(StringurlString) throwsIOException { ... } Basically, you defi ned a class that extends the AsyncTask class. In this case, there are two methods within the BackgroundTask class — doInBackground() and onPostExecute(). You put all the code that needs to be run asynchronously in the doInBackground() method. When the task is completed, the result is passed back via the onPostExecute() method. The onPostExecute() method is executed on the UI thread, hence it is thread safe to update the ImageView with the bitmap downloaded from the server. NOTE You will learn more about the AsyncTask class in Chapter 10 which covers developing services in Android. To perform the asynchronous tasks, simply create an instance of the BackgroundTask class and call its execute() method: @Override publicvoidonCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.main); new BackgroundTask().execute( “http://www.streetcar.org/mim/cable/images/cable-01.jpg”); } SummAry This chapter described the various ways to communicate with the outside world. You fi rst learned how to send and receive SMS messages. You then learned how to send e-mail messages from within your Android application. Besides SMS and e-mail, another way to communicate with the outside world is through the use of the HTTP protocol. Using the HTTP protocol, you can download data from a web server. One good application of this is to talk to Web services, whereby you need to parse XML fi les.
- 320. 298 ❘ Chapter 8 Messaging and Networking Exercises 1 . Name the two ways in which you can send SMS messages in your Android application. 2 . Name the permissions you need to declare in your AndroidManifest.xml file for sending and receiving SMS messages. 3. How do you notify an activity from a BroadcastReceiver? 4. Name the permissions you need to declare in your AndroidManifest.xml file for an HTTP connection. Answers to Exercises can be found in Appendix C.
- 321. Summary ❘ 299 ⊲⊲ What You Learned In This Chapter Topic Key Concepts Programmatically send- Use the SmsManager class. ing SMS messages Getting feedback on Use two PendingIntent objects in the sendTextMessage() method. messages sent Sending SMS messages Set the intent type to “vnd.android-dir/mms-sms”. using Intent Receiving SMS Implement a BroadcastReceiver and set it in the AndroidManifest messages .xml file. Sending e‑mail using Set the intent type to “message/rfc822”. Intent Establishing an HTTP Use the HttpURLConnection class. connection Accessing Web services Use the Document, DocumentBuilderFactory, and DocumentBuilder classes to parse the XML result returned by the Web service.
- 323. 9 Location-Based Services WhAt you Will leArn in thiS chApter ➤➤ How to display Google Maps in your Android application ➤➤ How to display the zoom controls on the map ➤➤ How to switch between the different map views ➤➤ How to add markers to maps ➤➤ How to get the address location touched on the map ➤➤ How to perform geocoding and reverse geocoding ➤➤ How to obtain geographical data using GPS, Cell-ID, and Wi-Fi triangulation ➤➤ How to monitor for a location We have all seen the explosive growth of mobile apps in recent years. One category of apps that is very popular is location-based services, commonly known as LBS. LBS apps track your location, and may offer additional services such as locating amenities nearby, as well as offer- ing suggestions for route planning, and so on. Of course, one of the key ingredients in a LBS app is maps, which present a visual representation of your location. In this chapter, you will learn how to make use of the Google Maps in your Android application, and how to manipulate it programmatically. In addition, you will learn how to obtain your geo- graphical location using the LocationManager class available in the Android SDK.
- 324. 302 ❘ Chapter 9 Location-Based Services Displaying Maps Google Maps is one of the many applications bundled with the Android platform. In addition to simply using the Maps application, you can also embed it into your own applications and make it do some very cool things. This section describes how to use Google Maps in your Android applications and programmatically perform the following: ➤➤ Change the views of Google Maps. ➤➤ Obtain the latitude and longitude of locations in Google Maps. ➤➤ Perform geocoding and reverse geocoding (translating an address to latitude and longitude and vice versa). ➤➤ Add markers to Google Maps. Creating the Project To get started, you need to first create an Android project so that you can display the Google Maps in your activity. Try It Out Creating the Project codefile LBS.zip available for download at Wrox.com 1 . Using Eclipse, create an Android project as shown in Figure 9-1. Figure 9-1
- 325. Displaying Maps ❘ 303 NOTE In order to use Google Maps in your Android application, you need to ensure that you check the Google APIs as your build target. Google Maps is not part of the standard Android SDK, so you need to find it in the Google APIs add-on. 2 . Once the project is created, observe the additional JAR file (maps.jar) located under the Google APIs folder (see Figure 9-2). Figure 9-2 How It Works This simple activity created an Android project that uses the Google APIs add-on. The Google APIs add- on includes the standard Android library, with the addition of the Maps library, as packaged within the maps.jar file. obtaining the maps Api key Beginning with the Android SDK release v1.0, you need to apply for a free Google Maps API key before you can integrate Google Maps into your Android application. When you apply for the key, you must also agree to Google’s terms of use, so be sure to read them carefully. To apply for a key, follow the series of steps outlined next. NOTE Google provides detailed documentation on applying for a Maps API key at http://code.google.com/android/add-ons/google-apis/mapkey.html. First, if you are testing the application on the Android Emulator or an Android device directly con- nected to your development machine, locate the SDK debug certificate located in the default folder (C:Users<username>.android for Windows 7 users). You can verify the existence of the debug certificate by going to Eclipse and selecting Window ➪ Preferences. Expand the Android item and select Build (see Figure 9-3). On the right side of the window, you will be able to see the debug cer- tificate’s location.
- 326. 304 ❘ chApter 9 location-BaSed ServiceS NOTE For Windows XP users, the default Android folder is C:DocumentsandSettings<username>LocalSettingsApplicationDataAndroid. Figure 9-3 The fi lename of the debug keystore is debug.keystore. This is the certificate that Eclipse uses to sign your application so that it may be run on the Android Emulator or devices. Using the debug keystore, you need to extract its MD5 fingerprint using the Keytool.exe application included with your JDK installation. This fi ngerprint is needed to apply for the free Google Maps key. You can usually fi nd the Keytool.exe in the C:ProgramFilesJava<JDK_version_number>bin folder. Issue the following command (see Figure 9-4) to extract the MD5 fi ngerprint: keytool.exe-list-aliasandroiddebugkey-keystore “C:Users<username>.androiddebug.keystore”-storepassandroid -keypassandroid Figure 9-4
- 327. Displaying Maps ❘ 305 In this example, my MD5 fi ngerprint is EF:7A:61:EA:AF:E0:B4:2D:FD:43:5E:1D:26:04:34:BA. Copy the MD5 certificate fi ngerprint and navigate your web browser to: http://code.google.com/ android/maps-api-signup.html. Follow the instructions on the page to complete the application and obtain the Google Maps key. When you are done, you should see something similar to what is shown in Figure 9-5. Figure 9-5 NOTE Although you can use the MD5 fingerprint of the debug keystore to obtain the Maps API key for debugging your application on the Android Emulator or devices, the key will not be valid if you try to deploy your Android application as an APK file. Once you are ready to deploy your application to the Android Market (or other methods of distribution), you need to reapply for a Maps API key using the certificate that will be used to sign your application. Chapter 11 dis- cusses this topic in more detail. displaying the map You are now ready to display Google Maps in your Android application. This involves two main tasks: ➤➤ Modify your AndroidManifest.xml file by adding both the <uses-library> element and the INTERNET permission. ➤➤ Add the MapView element to your UI.
- 328. 306 ❘ Chapter 9 Location-Based Services The following Try It Out shows you how. Try It Out Displaying Google Maps 1 . Using the project created in the previous section, add the following lines in bold to the main.xml file (be sure to replace the value of the apiKey attribute with the API key you obtained earlier): <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <com.google.android.maps.MapView android:id=”@+id/mapView” android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:enabled=”true” android:clickable=”true” android:apiKey=”<YOUR KEY>” /> </LinearLayout> 2 . Add the following lines in bold to the main.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.LBS” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <uses-library android:name=”com.google.android.maps” /> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”8” /> <uses-permission android:name=”android.permission.INTERNET”></uses-permission> </manifest> 3 . Add the following statements in bold to the MainActivity.java file. Note that MainActivity is now extending the MapActivity class. package net.learn2develop.LBS; import android.app.Activity;
- 329. Displaying Maps ❘ 307 import android.os.Bundle; import com.google.android.maps.MapActivity; public class MainActivity extends MapActivity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } @Override protected boolean isRouteDisplayed() { // TODO Auto-generated method stub return false; } } 4 . Press F11 to debug the application on the Android Emulator. Figure 9-6 shows Google Maps dis- playing in the activity of your application. Figure 9-6 How It Works In order to display Google Maps in your application, you first need to have the INTERNET permission in your manifest file. You then add the <com.google.android.maps.MapView> element to your UI file to embed the map within your activity. Very importantly, your activity must now extend the MapActivity class, which itself is an extension of the Activity class. For the MapActivity class, you need to implement one method: isRouteDisplayed(). This method is used for Google’s accounting purposes, and you should
- 330. 308 ❘ chApter 9 location-BaSed ServiceS return true for this method if you are displaying routing information on the map. For most simple cases, you can simply return false. cAn’t See the mAp? If instead of seeing Google Maps displayed you see an empty screen with grids, then most likely you are using the wrong API key in the main.xml fi le. It is also pos- sible that you omitted the INTERNET permission in your AndroidManifest.xml fi le. Finally, ensure that you have Internet access on your emulator/devices. If your program does not run (i.e., it crashes), then you probably forgot to add the following statement to the AndroidManifest.xml fi le: <uses-library android:name=”com.google.android.maps” /> Note its placement in the AndroidManifest.xml fi le; it should be within the <Application> element. displaying the zoom control The previous section showed how you can display Google Maps in your Android application. You can pan the map to any desired location and it will be updated on-the-fly. However, on the emulator there is no way to zoom in or out from a particular location (on a real Android device you can pinch the map to zoom it). Thus, in this section, you will learn how you can let users zoom in or out of the map using the built-in zoom controls. try it out Displaying the Built-in Zoom Controls 1 . Using the project created in the previous activity, add in the following statements in bold: packagenet.learn2develop.LBS; importandroid.app.Activity; importandroid.os.Bundle; importcom.google.android.maps.MapActivity; import com.google.android.maps.MapView; publicclassMainActivityextendsMapActivity{ MapView mapView; /**Calledwhentheactivityisfirstcreated.*/ @Override publicvoidonCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.main); mapView = (MapView) findViewById(R.id.mapView);
- 331. Displaying Maps ❘ 309 mapView.setBuiltInZoomControls(true); } @Override protected boolean isRouteDisplayed() { // TODO Auto-generated method stub return false; } } 2 . Press F11 to debug the application on the Android Emulator. Observe the built-in zoom controls that appear at the bottom of the map when you click and drag the map (see Figure 9-7). You can click the minus (–) icon to zoom out of the map and the plus (+) icon to zoom into the map. How It Works Figure 9-7 To display the built-in zoom controls, you first get a reference to the map and then call the setBuiltInZoomControls() method: mapView = (MapView) findViewById(R.id.mapView); mapView.setBuiltInZoomControls(true); Besides displaying the zoom controls, you can also programmatically zoom in or out of the map using the zoomIn() or zoomOut() method of the MapController class. The following Try It Out shows you how to achieve this. Try It Out Programmatically Zooming In or Out of the Map 1 . Using the project created in the previous activity, add the following statements in bold to the MainActivity.java file: package net.learn2develop.LBS; import android.app.Activity; import android.os.Bundle; import com.google.android.maps.MapActivity; import com.google.android.maps.MapView; import android.view.KeyEvent; import com.google.android.maps.MapController; public class MainActivity extends MapActivity { MapView mapView; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
- 332. 310 ❘ Chapter 9 Location-Based Services setContentView(R.layout.main); mapView = (MapView) findViewById(R.id.mapView); mapView.setBuiltInZoomControls(true); } public boolean onKeyDown(int keyCode, KeyEvent event) { MapController mc = mapView.getController(); switch (keyCode) { case KeyEvent.KEYCODE_3: mc.zoomIn(); break; case KeyEvent.KEYCODE_1: mc.zoomOut(); break; } return super.onKeyDown(keyCode, event); } @Override protected boolean isRouteDisplayed() { // TODO Auto-generated method stub return false; } } 2 . Press F11 to debug the application on the Android Emulator. You can now zoom into the map by pressing the numeric 3 key on the emulator. To zoom out of the map, press the numeric 1 key. How It Works Do To handle key presses on your activity, you handle the onKeyDown event: public boolean onKeyDown(int keyCode, KeyEvent event) { //... } To manage the panning and zooming of the map, you need to obtain an instance of the MapController class from the MapView object. The MapController class contains the zoomIn() and zoomOut() methods (plus some other methods to control the map) to enable users to zoom in or out of the map, respectively. Changing Views By default, Google Maps is displayed in map view, which is basically drawings of streets and places of interest. You can also set Google Maps to display in satellite view using the setSatellite() method of the MapView class: @Override public void onCreate(Bundle savedInstanceState) {
- 333. Displaying Maps ❘ 311 super.onCreate(savedInstanceState); setContentView(R.layout.main); mapView = (MapView) findViewById(R.id.mapView); mapView.setBuiltInZoomControls(true); mapView.setSatellite(true); } Figure 9-8 shows Google Maps displayed in satellite view. Figure 9-8 Besides satellite view, you can also display the map in street view (which highlights all the streets on the map) using the setStreetView() method. Figure 9-9 shows the map displaying a location in both street view (left) and satellite view (right). @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mapView = (MapView) findViewById(R.id.mapView); mapView.setBuiltInZoomControls(true); mapView.setSatellite(true); mapView.setStreetView(true); } If you want to display traffic conditions on the map, use the setTraffic() method: mapView.setTraffic(true);
- 334. 312 ❘ Chapter 9 Location-Based Services Figure 9-9 Figure 9-10 shows the map displaying the current traffic con- ditions. The different colors reflect the varying traffic condi- tions. In general, green color equates to smooth traffic of about 50 miles per hour, yellow equates to moderate traffic of about 25-50 miles per hour, and red equates to slow traf- fic of about less than 25 miles per hour. Note that the traffic information is only available in major cities in the United States, France, Britain, Australia, and Canada, with new cities and countries frequently added. Navigating to a Specific Location By default, Google Maps displays the map of the United States when it is first loaded. However, you can also set Google Maps to display a particular location. In this case, you can use the animateTo() method of the MapController class. The following Try It Out shows how you can programmati- cally animate Google Maps to a particular location. Figure 9-10
- 335. Displaying Maps ❘ 313 Try It Out Navigating the Map to Display a Specific Location 1 . Using the project created in the previous activity, add the following statements in bold to the MainActivity.java file: package net.learn2develop.LBS; import android.app.Activity; import android.os.Bundle; import android.view.KeyEvent; import com.google.android.maps.MapActivity; import com.google.android.maps.MapController; import com.google.android.maps.MapView; import com.google.android.maps.GeoPoint; public class MainActivity extends MapActivity { MapView mapView; MapController mc; GeoPoint p; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mapView = (MapView) findViewById(R.id.mapView); mapView.setBuiltInZoomControls(true); //mapView.setSatellite(true); mapView.setStreetView(true); mc = mapView.getController(); String coordinates[] = {“1.352566007”, “103.78921587”}; double lat = Double.parseDouble(coordinates[0]); double lng = Double.parseDouble(coordinates[1]); p = new GeoPoint( (int) (lat * 1E6), (int) (lng * 1E6)); mc.animateTo(p); mc.setZoom(13); mapView.invalidate(); } public boolean onKeyDown(int keyCode, KeyEvent event) {
- 336. 314 ❘ Chapter 9 Location-Based Services MapController mc = mapView.getController(); switch (keyCode) { case KeyEvent.KEYCODE_3: mc.zoomIn(); break; case KeyEvent.KEYCODE_1: mc.zoomOut(); break; } return super.onKeyDown(keyCode, event); } @Override protected boolean isRouteDisplayed() { // TODO Auto-generated method stub return false; } } 2 . Press F11 to debug the application on the Android Emulator. When the map is loaded, observe that it now animates to a particular location in Singapore (see Figure 9-11). Figure 9-11 How It Works In the preceding code, you first obtain a map controller from the MapView instance and assign it to a MapController object (mc). You then use a GeoPoint object to represent a geographical location. Note that for this class, the latitude and longitude of a location are represented in micro degrees. This means
- 337. Displaying Maps ❘ 315 that they are stored as integer values. For a latitude value of 40.747778, for example, you need to multi- ply it by 1e6 (which is one million) to obtain 40747778. To navigate the map to a particular location, you can use the animateTo() method of the MapController class. The setZoom() method enables you to specify the zoom level at which the map is displayed (the bigger the number, the more details you see on the map). The invalidate() method forces the MapView to be redrawn. Adding Markers Adding markers to a map to indicate places of interest enables your users to easily locate the places they are looking for. The following Try It Out shows you how to add a marker to Google Maps. Try It Out Adding Markers to the Map 1 . Create a GIF image containing a pushpin (see Figure 9-12) and copy it into the res/drawable-mdpi folder of the project. For the best effect, make the background of the image transparent so that it does not block parts of the map when the image is added to the map. 2 . Using the project created in the previous activity, add the following statements in bold to the MainActivity.java file: Figure 9-12 package net.learn2develop.LBS; import android.app.Activity; import android.os.Bundle; import android.view.KeyEvent; import com.google.android.maps.GeoPoint; import com.google.android.maps.MapActivity; import com.google.android.maps.MapController; import com.google.android.maps.MapView; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.graphics.Point; import com.google.android.maps.Overlay; import java.util.List; public class MainActivity extends MapActivity { MapView mapView; MapController mc; GeoPoint p; class MapOverlay extends com.google.android.maps.Overlay { @Override
- 338. 316 ❘ Chapter 9 Location-Based Services public boolean draw(Canvas canvas, MapView mapView, boolean shadow, long when) { super.draw(canvas, mapView, shadow); //---translate the GeoPoint to screen pixels--- Point screenPts = new Point(); mapView.getProjection().toPixels(p, screenPts); //---add the marker--- Bitmap bmp = BitmapFactory.decodeResource( getResources(), R.drawable.pushpin); canvas.drawBitmap(bmp, screenPts.x, screenPts.y-50, null); return true; } } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mapView = (MapView) findViewById(R.id.mapView); mapView.setBuiltInZoomControls(true); //mapView.setSatellite(true); //mapView.setStreetView(true); mc = mapView.getController(); String coordinates[] = {“1.352566007”, “103.78921587”}; double lat = Double.parseDouble(coordinates[0]); double lng = Double.parseDouble(coordinates[1]); p = new GeoPoint( (int) (lat * 1E6), (int) (lng * 1E6)); mc.animateTo(p); mc.setZoom(13); //---Add a location marker--- MapOverlay mapOverlay = new MapOverlay(); List<Overlay> listOfOverlays = mapView.getOverlays(); listOfOverlays.clear(); listOfOverlays.add(mapOverlay); mapView.invalidate(); } public boolean onKeyDown(int keyCode, KeyEvent event) { MapController mc = mapView.getController(); switch (keyCode)
- 339. Displaying Maps ❘ 317 { case KeyEvent.KEYCODE_3: mc.zoomIn(); break; case KeyEvent.KEYCODE_1: mc.zoomOut(); break; } return super.onKeyDown(keyCode, event); } @Override protected boolean isRouteDisplayed() { // TODO Auto-generated method stub return false; } } 3 . Press F11 to debug the application on the Android Emulator. Figure 9-13 shows the marker added to the map. Figure 9-13 How It Works To add a marker to the map, you first need to define a class that extends the Overlay class: class MapOverlay extends com.google.android.maps.Overlay { @Override public boolean draw(Canvas canvas, MapView mapView,
- 340. 318 ❘ Chapter 9 Location-Based Services boolean shadow, long when) { //... } } An overlay represents an individual item that you can draw on the map. You can add as many overlays as you want. In the MapOverlay class, override the draw() method so that you can draw the pushpin image on the map. In particular, note that you need to translate the geographical location (represented by a GeoPoint object, p) into screen coordinates: //---translate the GeoPoint to screen pixels--- Point screenPts = new Point(); mapView.getProjection().toPixels(p, screenPts); Because you want the pointed tip of the pushpin to indicate the position of the location, you need to deduct the height of the image (which is 50 pixels) from the y coordinate of the point (see Figure 9-14) and draw the image at that location: //---add the marker--- Bitmap bmp = BitmapFactory.decodeResource( getResources(), R.drawable.pushpin); canvas.drawBitmap(bmp, screenPts.x, screenPts.y-50, null); Figure 9-14 To add the marker, create an instance of the MapOverlay class and add it to the list of overlays available on the MapView object: //---Add a location marker--- MapOverlay mapOverlay = new MapOverlay(); List<Overlay> listOfOverlays = mapView.getOverlays(); listOfOverlays.clear(); listOfOverlays.add(mapOverlay); Getting the Location That Was Touched After using Google Maps for a while, you may want to know the latitude and longitude of a location corresponding to the position on the screen that was just touched. Knowing this information is very useful, as you can determine a location’s address, a process known as reverse geocoding (you will learn how this is done in the next section).
- 341. Displaying Maps ❘ 319 If you have added an overlay to the map, you can override the onTouchEvent() method within the MapOverlay class. This method is fired every time the user touches the map. This method has two parameters: MotionEvent and MapView. Using the MotionEvent parameter, you can determine whether the user has lifted his or her finger from the screen using the getAction() method. In the following code snippet, if the user has touched and then lifted the finger, you display the latitude and longitude of the location touched: import android.view.MotionEvent; import android.widget.Toast; //... class MapOverlay extends com.google.android.maps.Overlay { @Override public boolean draw(Canvas canvas, MapView mapView, boolean shadow, long when) { super.draw(canvas, mapView, shadow); //---translate the GeoPoint to screen pixels--- Point screenPts = new Point(); mapView.getProjection().toPixels(p, screenPts); //---add the marker--- Bitmap bmp = BitmapFactory.decodeResource( getResources(), R.drawable.pushpin); canvas.drawBitmap(bmp, screenPts.x, screenPts.y-50, null); return true; } @Override public boolean onTouchEvent(MotionEvent event, MapView mapView) { //---when user lifts his finger--- if (event.getAction() == 1) { GeoPoint p = mapView.getProjection().fromPixels( (int) event.getX(), (int) event.getY()); Toast.makeText(getBaseContext(), “Location: “+ p.getLatitudeE6() / 1E6 + “,” + p.getLongitudeE6() /1E6 , Toast.LENGTH_SHORT).show(); } return false; } } The getProjection() method returns a projection for converting between screen-pixel coordinates and latitude/longitude coordinates. The fromPixels() method then converts the screen coordinates into a GeoPoint object. Figure 9-15 shows the map displaying a set of coordinates when the user clicks a location on the map.
- 342. 320 ❘ Chapter 9 Location-Based Services Figure 9-15 Geocoding and Reverse Geocoding As mentioned in the preceding section, if you know the latitude and longitude of a location, you can find out its address using a process known as reverse geocoding. Google Maps in Android supports this via the Geocoder class. The following code snippet shows how you can retrieve the address of a location just touched using the getFromLocation() method: import android.location.Address; import android.location.Geocoder; import java.util.Locale; import java.io.IOException; //... @Override public boolean onTouchEvent(MotionEvent event, MapView mapView) { //---when user lifts his finger--- if (event.getAction() == 1) { GeoPoint p = mapView.getProjection().fromPixels( (int) event.getX(), (int) event.getY()); /* Toast.makeText(getBaseContext(), “Location: “+ p.getLatitudeE6() / 1E6 + “,” + p.getLongitudeE6() /1E6 , Toast.LENGTH_SHORT).show();
- 343. Displaying Maps ❘ 321 */ Geocoder geoCoder = new Geocoder( getBaseContext(), Locale.getDefault()); try { List<Address> addresses = geoCoder.getFromLocation( p.getLatitudeE6() / 1E6, p.getLongitudeE6() / 1E6, 1); String add = “”; if (addresses.size() > 0) { for (int i=0; i<addresses.get(0).getMaxAddressLineIndex(); i++) add += addresses.get(0).getAddressLine(i) + “n”; } Toast.makeText(getBaseContext(), add, Toast.LENGTH_SHORT).show(); } catch (IOException e) { e.printStackTrace(); } return true; } return false; } } The Geocoder object converts the latitude and longitude into an address using the getFromLocation() method. Once the address is obtained, you display it using the Toast class. Figure 9-16 shows the application displaying the address of a location that was touched on the map. If you know the address of a location but want to know its latitude and longitude, you can do so via geocoding. Again, you can use the Geocoder class for this purpose. The following code shows how you can find the exact location of the Empire State Building by using the getFromLocationName() method: //---geo-coding--- Geocoder geoCoder = new Geocoder(this, Locale.getDefault()); try { List<Address> addresses = geoCoder.getFromLocationName( “empire state building”, 5); String add = “”; if (addresses.size() > 0) { p = new GeoPoint( (int) (addresses.get(0).getLatitude() * 1E6), (int) (addresses.get(0).getLongitude() * 1E6)); mc.animateTo(p); mapView.invalidate(); } } catch (IOException e) { e.printStackTrace(); }
- 344. 322 ❘ Chapter 9 Location-Based Services Figure 9-17 shows the map navigating to the location of the Empire State Building. Figure 9-16 Figure 9-17 Getting Location Data Nowadays, mobile devices are commonly equipped with GPS receivers. Because of the many satellites orbiting the earth, you can use a GPS receiver to find your location easily. However, GPS requires a clear sky to work and hence does not always work indoors or where satellites can’t penetrate (such as a tunnel through a mountain). Another effective way to locate your position is through cell tower triangulation. When a mobile phone is switched on, it is constantly in contact with base stations surrounding it. By knowing the identity of cell towers, it is possible to translate this information into a physical location through the use of various databases containing the cell towers’ identities and their exact geographical locations. The advantage of cell tower triangulation is that it works indoors, without the need to obtain information from satellites. However, it is not as precise as GPS because its accuracy depends on overlapping signal coverage, which varies quite a bit. Cell tower triangulation works best in densely populated areas where the cell towers are closely located. A third method of locating your position is to rely on Wi-Fi triangulation. Rather than connect to cell towers, the device connects to a Wi-Fi network and checks the service provider against databases to determine the location serviced by the provider. Of the three methods described here, Wi-Fi triangu- lation is the least accurate. On the Android, the SDK provides the LocationManager class to help your device determine the user’s physical location. The following Try It Out shows you how this is done in code. Try It Out Navigating the Map to a Specific Location Using the Location Manager Class 1 . Using the same project created in the previous section, add the following statements in bold to the MainActivity.java file: package net.learn2develop.LBS; import android.app.Activity;
- 345. Getting Location Data ❘ 323 import android.content.Context; //... //... import android.location.Location; import android.location.LocationListener; import android.location.LocationManager; public class MainActivity extends MapActivity { MapView mapView; MapController mc; GeoPoint p; private LocationManager lm; private LocationListener locationListener; class MapOverlay extends com.google.android.maps.Overlay { //... } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mapView = (MapView) findViewById(R.id.mapView); mapView.setBuiltInZoomControls(true); mc = mapView.getController(); //---navigate to a point first--- String coordinates[] = {“1.352566007”, “103.78921587”}; double lat = Double.parseDouble(coordinates[0]); double lng = Double.parseDouble(coordinates[1]); p = new GeoPoint( (int) (lat * 1E6), (int) (lng * 1E6)); mc.animateTo(p); mc.setZoom(13); //---Add a location marker--- //... //---reverse geo-coding--- //... //---use the LocationManager class to obtain locations data--- lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); locationListener = new MyLocationListener(); lm.requestLocationUpdates( LocationManager.GPS_PROVIDER, 0,
- 346. 324 ❘ Chapter 9 Location-Based Services 0, locationListener); } private class MyLocationListener implements LocationListener { @Override public void onLocationChanged(Location loc) { if (loc != null) { Toast.makeText(getBaseContext(), “Location changed : Lat: “ + loc.getLatitude() + “ Lng: “ + loc.getLongitude(), Toast.LENGTH_SHORT).show(); } p = new GeoPoint( (int) (loc.getLatitude() * 1E6), (int) (loc.getLongitude() * 1E6)); mc.animateTo(p); mc.setZoom(18); } @Override public void onProviderDisabled(String provider) { } @Override public void onProviderEnabled(String provider) { } @Override public void onStatusChanged(String provider, int status, Bundle extras) { } } public boolean onKeyDown(int keyCode, KeyEvent event) { //... } @Override protected boolean isRouteDisplayed() { // TODO Auto-generated method stub return false; } } 2 . Press F11 to debug the application on the Android Emulator. 3. To simulate GPS data received by the Android Emulator, you use the Location Controls tool (see Figure 9-18) located in the DDMS perspective.
- 347. Getting Location Data ❘ 325 4 . Ensure that you have first selected the emulator in the Devices tab. Then, in the Emulator Control tab, locate the Location Controls tool and select the Manual tab. Enter a latitude and longitude and click the Send button. 5. Observe that the map on the emulator now animates to another location (see Figure 9-19). This proves that the application has received the GPS data. Figure 9-18 Figure 9-19
- 348. 326 ❘ Chapter 9 Location-Based Services How It Works In Android, location-based services are provided by the LocationManager class, located in the android .location package. Using the LocationManager class, your application can obtain periodic updates of the device’s geographical locations, as well as fire an intent when it enters the proximity of a certain location. In the MainActivity.java file, you first obtain a reference to the LocationManager class using the getSystemService() method. To be notified whenever there is a change in location, you need to reg- ister a request for location changes so that your program can be notified periodically. This is done via the requestLocationUpdates() method: lm.requestLocationUpdates( LocationManager.GPS_PROVIDER, 0, 0, locationListener); This method takes four parameters: ➤➤ provider — The name of the provider with which you register. In this case, you are using GPS to obtain your geographical location data. ➤➤ minTime — The minimum time interval for notifications, in milliseconds ➤➤ minDistance — The minimum distance interval for notifications, in meters ➤➤ listener — An object whose onLocationChanged() method will be called for each location update The MyLocationListener class implements the LocationListener abstract class. You need to override four methods in this implementation: ➤➤ onLocationChanged(Location location) — Called when the location has changed ➤➤ onProviderDisabled(String provider) — Called when the provider is disabled by the user ➤➤ onProviderEnabled(String provider) — Called when the provider is enabled by the user ➤➤ onStatusChanged(String provider, int status, Bundle extras) — Called when the provider status changes In this example, you’re more interested in what happens when a location changes, so you’ll write some code in the onLocationChanged() method. Specifically, when a location changes, you will display a small dialog on the screen showing the new location information: latitude and longitude. You show this dialog using the Toast class. If you want to use Cell-ID and Wi-Fi triangulation (important for indoor use) for obtaining your location data, you can use the network location provider, like this: lm.requestLocationUpdates( LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
- 349. Summary ❘ 327 You can combine both the GPS location provider with the network location provider within your application. Monitoring a Location One very cool feature of the LocationManager class is its ability to monitor a specific location. This is achieved using the addProximityAlert() method. The following code snippet shows how to moni- tor a particular location so that if the user is within a five-meter radius from that location, your application will fire an intent to launch the web browser: //---use the LocationManager class to obtain locations data--- lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); //---PendingIntent to launch activity if the user is within some locations--- PendingIntent pendIntent = PendingIntent.getActivity( this, 0, new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“http://www.amazon.com”)), 0); lm.addProximityAlert(37.422006, -122.084095, 5, -1, pendIntent); The addProximityAlert() method takes five arguments: latitude, longitude, radius (in meters), expi- ration (time for the proximity alert to be valid, after which it will be deleted; -1 for no expiration), and the pending intent. Note that if the Android device’s screen goes to sleep, the proximity is also checked once every four minutes in order to preserve the battery life of the device. Summary This chapter took a whirlwind tour of the MapView object, which displays Google Maps in your Android application. You have learned the various ways in which the map can be manipulated, and you have also seen how you can obtain geographical location data using the various network provid- ers: GPS, Cell-ID, or Wi-Fi triangulation. Exercises 1 . If you have embedded the Google Maps API into your Android application but it does not show the map when the application is loaded, what could be the likely reasons? 2 . What is the difference between geocoding and reverse geocoding? 3. Name the two location providers that you can use to obtain your location data. 4. What is the method for monitoring a location? Answers to Exercises can be found in Appendix C.
- 350. 328 ❘ Chapter 9 Location-Based Services ⊲⊲ What You Learned In This Chapter Topic Key Concepts Displaying the <com.google.android.maps.MapView MapView android:id=”@+id/mapView” android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:enabled=”true” android:clickable=”true” android:apiKey=”0K2eMNyjc5HFPsiobLh6uLHb8F9ZFmh4uIm7VTA” /> Referencing the <uses-library android:name=”com.google.android.maps” /> Map library Displaying the mapView.setBuiltInZoomControls(true); zoom controls Programmatically mc.zoomIn(); zooming in or out mc.zoomOut(); of the map Changing views mapView.setSatellite(true); mapView.setStreetView(true); mapView.setTraffic(true); Animating to mc = mapView.getController(); a particular String coordinates[] = {“1.352566007”, “103.78921587”}; double lat = Double.parseDouble(coordinates[0]); location double lng = Double.parseDouble(coordinates[1]); p = new GeoPoint( (int) (lat * 1E6), (int) (lng * 1E6)); mc.animateTo(p); Adding markers Implement an Overlay class and override the draw() method Getting the loca- GeoPoint p = mapView.getProjection().fromPixels( tion of the map (int) event.getX(), (int) event.getY()); touched Geocoding Use the Geocoder class and reverse geocoding
- 351. Summary ❘ 329 Topic Key Concepts Obtaining private LocationManager lm; location data //... lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); locationListener = new MyLocationListener(); lm.requestLocationUpdates( LocationManager.GPS_PROVIDER, 0, 0, locationListener); //... private class MyLocationListener implements LocationListener { @Override public void onLocationChanged(Location loc) { if (loc != null) { } } @Override public void onProviderDisabled(String provider) { } @Override public void onProviderEnabled(String provider) { } @Override public void onStatusChanged(String provider, int status, Bundle extras) { } } Monitoring a lm.addProximityAlert(37.422006, -122.084095, 5, -1, pendIntent); location
- 353. 10 Developing Android Services WhAt you Will leArn in thiS chApter ➤➤ How to create a service that runs in the background ➤➤ How to perform long-running tasks in a separate thread ➤➤ How to perform repeated tasks in a service ➤➤ How an activity and a service communicate A service is an application in Android that runs in the background without needing to interact with the user. For example, while using an application, you may want to play some background music at the same time. In this case, the code that is playing the background music has no need to interact with the user, and hence it can be run as a service. Services are also ideal for situa- Do tions in which there is no need to present a UI to the user. A good example of this scenario is an application that continually logs the geographical coordinates of the device. In this case, you can write a service to do that in the background. In this chapter, you will learn how to create your own services and use them to perform background tasks asynchronously. creAting your oWn ServiceS The best way to understand how a service works is by creating one. The following Try It Out shows you the steps to create a simple service. Subsequent sections will add more functionality to this service. For now, you will learn how to start and stop a service. try it out Creating a Simple Service codefile Services.zip available for download at Wrox.com 1 . Using Eclipse, create a new Android project and name it as shown in Figure 10-1.
- 354. 332 ❘ Chapter 10 Developing Android Services Figure 10-1 2 . Add a new class file to the project and name it MyService.java. Populate it with the following code: package net.learn2develop.Services; import android.app.Service; import android.content.Intent; import android.os.IBinder; import android.widget.Toast; public class MyService extends Service { @Override public IBinder onBind(Intent arg0) { return null; } @Override public int onStartCommand(Intent intent, int flags, int startId) { // We want this service to continue running until it is explicitly // stopped, so return sticky. Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show(); return START_STICKY; } @Override public void onDestroy() { super.onDestroy();
- 355. Creating Your Own Services ❘ 333 Toast.makeText(this, “Service Destroyed”, Toast.LENGTH_LONG).show(); } } 3 . In the AndroidManifest.xml file, add the following statement in bold: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Services” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> <service android:name=”.MyService” /> </application> <uses-sdk android:minSdkVersion=”9” /> </manifest> 4 . In the main.xml file, add the following statements in bold: <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <Button android:id=”@+id/btnStartService” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Start Service” /> <Button android:id=”@+id/btnStopService” android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Stop Service” /> </LinearLayout> 5 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Services; import android.app.Activity; import android.os.Bundle; import android.content.Intent; import android.view.View; import android.widget.Button; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override
- 356. 334 ❘ Chapter 10 Developing Android Services public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button btnStart = (Button) findViewById(R.id.btnStartService); btnStart.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { startService(new Intent(getBaseContext(), MyService.class)); } }); Button btnStop = (Button) findViewById(R.id.btnStopService); btnStop.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { stopService(new Intent(getBaseContext(), MyService.class)); } }); } } 6 . Press F11 to debug the application on the Android Emulator. 7. Clicking the Start Service button will start the service (see Figure 10-2). To stop the service, click the Stop Service button. Figure 10-2 How It Works This example demonstrated the simplest service that you can create. The service itself is not doing anything useful, of course, but it serves to illustrate the creation process.
- 357. Creating Your Own Services ❘ 335 First, you defined a class that extends the Service base class. All services extend the Service class: public class MyService extends Service { } Within the MyService class, you implemented three methods: @Override public IBinder onBind(Intent arg0) {...} @Override public int onStartCommand(Intent intent, int flags, int startId) {...} @Override public void onDestroy() {...} The onBind() method enables you to bind an activity to a service. This in turn enables an activity to directly access members and methods inside a service. For now, you simply return a null for this method. Later in this chapter you will learn more about binding. The onStartCommand() method is called when you start the service explicitly using the startService() method (discussed shortly). This method signifies the start of the service, and you code it to do the things you need to do for your service. In this method, you returned the constant START_STICKY so that the service will continue to run until it is explicitly stopped. The onDestroy() method is called when the service is stopped using the stopService() method. This is where you clean up the resources used by your service. All services that you have created must be declared in the AndroidManifest.xml file, like this: <service android:name=”.MyService” /> If you want your service to be available to other applications, you can always add an intent filter with an action name, like this: <service android:name=”.MyService”> <intent-filter> <action android:name=”net.learn2develop.MyService” /> </intent-filter> </service> To start a service, you use the startService() method, like this: startService(new Intent(getBaseContext(), MyService.class)); If you are calling an external service, then the call to the startService() method will look like this: startService(new Intent(“net.learn2develop.MyService”)); To stop a service, use the stopService() method, like this: stopService(new Intent(getBaseContext(), MyService.class));
- 358. 336 ❘ Chapter 10 Developing Android Services Performing Long-Running Tasks in a Service Because the service you created in the previous section does not do anything useful, in this section you will modify the service so that it perform a task. In the following Try It Out, you will simulate the service of downloading a file from the Internet. Try It Out Making Your Service Useful 1 . Using the same project created in the previous section, add the following statements in bold to the MainActivity.java file: package net.learn2develop.Services; import android.app.Service; import android.content.Intent; import android.os.IBinder; import android.widget.Toast; import java.net.MalformedURLException; import java.net.URL; public class MyService extends Service { @Override public IBinder onBind(Intent arg0) { return null; } @Override public int onStartCommand(Intent intent, int flags, int startId) { // We want this service to continue running until it is explicitly // stopped, so return sticky. Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show(); try { int result = DownloadFile(new URL(“http://www.amazon.com/somefile.pdf”)); Toast.makeText(getBaseContext(), “Downloaded “ + result + “ bytes”, Toast.LENGTH_LONG).show(); } catch (MalformedURLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return START_STICKY; } @Override public void onDestroy() { super.onDestroy(); Toast.makeText(this, “Service Destroyed”, Toast.LENGTH_LONG).show(); } private int DownloadFile(URL url) { try { //---simulate taking some time to download a file---
- 359. Creating Your Own Services ❘ 337 Thread.sleep(5000); } catch (InterruptedException e) { e.printStackTrace(); } //---return an arbitrary number representing // the size of the file downloaded--- return 100; } } 2 . Press F11 to debug the application on the Android Emulator. 3. Click the Start Service button to start the service to download the file. Observe that the activity will be frozen for a few seconds (see Figure 10-3) before the Toast class displays the “Downloaded 100 bytes” message. Figure 10-3 How It Works In this example, your service calls the DownloadFile() method to simulate downloading a file from a given URL. This method returns the total number of bytes downloaded (which you have hardcoded as 100). To simulate the delays experienced by the service when downloading the file, you used the Thread .Sleep() method to pause the service for five seconds (5,000 milliseconds). As you start the service, note that the activity is suspended for about five seconds, which is the time taken for the file to be downloaded from the Internet. During this time, the entire activity is not responsive, proving a very important point: The service runs on the same thread as your activity. In this case, because the service is suspended for five seconds, so is the activity.
- 360. 338 ❘ Chapter 10 Developing Android Services Hence, for a long-running service, it is important that you put all long-running code into a separate thread so that it does not tie up the application that calls it. The following Try It Out shows you how. Try It Out Performing Tasks in a Service Asynchronously 1 . Using the same project created in the previous section, add the following statements in bold to the MyService.java file: package net.learn2develop.Services; import android.app.Service; import android.content.Intent; import android.os.IBinder; import android.util.Log; import android.widget.Toast; import java.net.MalformedURLException; import java.net.URL; import android.os.AsyncTask; public class MyService extends Service { @Override public IBinder onBind(Intent arg0) { return null; } @Override public int onStartCommand(Intent intent, int flags, int startId) { // We want this service to continue running until it is explicitly // stopped, so return sticky. Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show(); try { new DoBackgroundTask().execute( new URL(“http://www.amazon.com/somefiles.pdf”), new URL(“http://www.wrox.com/somefiles.pdf”), new URL(“http://www.google.com/somefiles.pdf”), new URL(“http://www.learn2develop.net/somefiles.pdf”)); } catch (MalformedURLException e) { e.printStackTrace(); } return START_STICKY; } @Override public void onDestroy() { super.onDestroy(); Toast.makeText(this, “Service Destroyed”, Toast.LENGTH_LONG).show(); } private int DownloadFile(URL url) {
- 361. Creating Your Own Services ❘ 339 try { //---simulate taking some time to download a file--- Thread.sleep(5000); } catch (InterruptedException e) { e.printStackTrace(); } //---return an arbitrary number representing // the size of the file downloaded--- return 100; } private class DoBackgroundTask extends AsyncTask<URL, Integer, Long> { protected Long doInBackground(URL... urls) { int count = urls.length; long totalBytesDownloaded = 0; for (int i = 0; i < count; i++) { totalBytesDownloaded += DownloadFile(urls[i]); //---calculate percentage downloaded and // report its progress--- publishProgress((int) (((i+1) / (float) count) * 100)); } return totalBytesDownloaded; } protected void onProgressUpdate(Integer... progress) { Log.d(“Downloading files”, String.valueOf(progress[0]) + “% downloaded”); Toast.makeText(getBaseContext(), String.valueOf(progress[0]) + “% downloaded”, Toast.LENGTH_LONG).show(); } protected void onPostExecute(Long result) { Toast.makeText(getBaseContext(), “Downloaded “ + result + “ bytes”, Toast.LENGTH_LONG).show(); stopSelf(); } } } 2 . Press F11 to debug the application on the Android Emulator. 3 . Click the Start Service button. The Toast class will display a message indicating what percentage of the download is completed (see Figure 10-4). You should see four of them: 25%, 50%, 75%, and 100%. 4 . You will also observe the following output in the LogCat window: 01-16 02:56:29.051: DEBUG/Downloading files(8844): 25% downloaded 01-16 02:56:34.071: DEBUG/Downloading files(8844): 50% downloaded 01-16 02:56:39.106: DEBUG/Downloading files(8844): 75% downloaded 01-16 02:56:44.173: DEBUG/Downloading files(8844): 100% downloaded
- 362. 340 ❘ Chapter 10 Developing Android Services Figure 10-4 How It Works This example illustrates one way in which you can execute a task asynchronously within your service. You do so by creating an inner class that extends the AsyncTask class. The AsyncTask class enables you to perform background execution without needing to manually handle threads and handlers. The DoBackgroundTask class extends the AsyncTask class by specifying three generic types: private class DoBackgroundTask extends AsyncTask<URL, Integer, Long> { In this case, the three types specified are URL, Integer and Long. These three types specify the data type used by the following three methods that you implement in an AsyncTask class: ➤➤ doInBackground() — This method takes an array of the first generic type specified earlier. In this case, the type is URL. This method is executed in the background thread and is where you put your long-running code. To report the progress of your task, you call the publishProgress() method, which invokes the next method, onProgressUpdate(), which you implement in an AsyncTask class. The return type of this method takes the third generic type specified earlier, which is Long in this case. ➤➤ onProgressUpdate() — This method is invoked in the UI thread and is called when you call the publishProgress() method. It takes an array of the second generic type specified earlier. In this case, the type is Integer. Use this method to report the progress of the background task to the user. ➤➤ onPostExecute() — This method is invoked in the UI thread and is called when the doInBackground() method has finished execution. This method takes an argument of the third generic type specified earlier, which in this case is a Long.
- 363. Creating Your Own Services ❘ 341 To download multiple files in the background, you created an instance of the DoBackgroundTask class and then called its execute() method by passing in an array of URLs: try { new DoBackgroundTask().execute( new URL(“http://www.amazon.com/somefiles.pdf”), new URL(“http://www.wrox.com/somefiles.pdf”), new URL(“http://www.google.com/somefiles.pdf”), new URL(“http://www.learn2develop.net/somefiles.pdf”)); } catch (MalformedURLException e) { // TODO Auto-generated catch block e.printStackTrace(); } The preceding causes the service to download the files in the background, and reports the progress as a percentage of files downloaded. More important, the activity remains responsive while the files are downloaded in the background, on a separate thread. Note that when the background thread has finished execution, you need to manually call the stopSelf() method to stop the service: protected void onPostExecute(Long result) { Toast.makeText(getBaseContext(), “Downloaded “ + result + “ bytes”, Toast.LENGTH_LONG).show(); stopSelf(); } The stopSelf() method is the equivalent of calling the stopService() method to stop the service. Performing Repeated Tasks in a Service Besides performing long-running tasks in a service, you might also perform some repeated tasks in a service. For example, you may write an alarm clock service that runs persistently in the back- ground. In this case, your service may need to periodically execute some code to check whether a prescheduled time has been reached so that an alarm can be sounded. To execute a block of code to be executed at a regular time interval, you can use the Timer class within your service. The following Try It Out shows you how. Try It Out Running Repeated Tasks Using the Timer Class 1 . Using the same project created in the previous section, add the following statements in bold to the MyService.java file: package net.learn2develop.Services; import android.app.Service; import android.content.Intent; import android.os.AsyncTask; import android.os.IBinder; import android.util.Log;
- 364. 342 ❘ Chapter 10 Developing Android Services import android.widget.Toast; import java.net.URL; import java.util.Timer; import java.util.TimerTask; public class MyService extends Service { int counter = 0; static final int UPDATE_INTERVAL = 1000; private Timer timer = new Timer(); @Override public IBinder onBind(Intent arg0) { return null; } @Override public int onStartCommand(Intent intent, int flags, int startId) { // We want this service to continue running until it is explicitly // stopped, so return sticky. Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show(); doSomethingRepeatedly(); return START_STICKY; } private void doSomethingRepeatedly() { timer.scheduleAtFixedRate( new TimerTask() { public void run() { Log.d(“MyService”, String.valueOf(++counter)); } }, 0, UPDATE_INTERVAL); } @Override public void onDestroy() { super.onDestroy(); if (timer != null){ timer.cancel(); } Toast.makeText(this, “Service Destroyed”, Toast.LENGTH_LONG).show(); } } 2 . Press F11 to debug the application on the Android Emulator. 3. Click the Start Service button. 4. Observe the output displayed in the LogCat window: 01-16 15:12:04.364: DEBUG/MyService(495): 1 01-16 15:12:05.384: DEBUG/MyService(495): 2 01-16 15:12:06.386: DEBUG/MyService(495): 3 01-16 15:12:07.389: DEBUG/MyService(495): 4 01-16 15:12:08.364: DEBUG/MyService(495): 5 01-16 15:12:09.427: DEBUG/MyService(495): 6 01-16 15:12:10.374: DEBUG/MyService(495): 7
- 365. Creating Your Own Services ❘ 343 How It Works In this example, you created a Timer object and called its scheduleAtFixedRate() method inside the doSomethingRepeatedly() method that you have defined: private void doSomethingRepeatedly() { timer.scheduleAtFixedRate(new TimerTask() { public void run() { Log.d(“MyService”, String.valueOf(++counter)); } }, 0, UPDATE_INTERVAL); } You passed an instance of the TimerTask class to the scheduleAtFixedRate() method so that you can execute the block of code within the run() method repeatedly. The second parameter to the scheduleAtFixedRate() method specifies the amount of time, in milliseconds, before first execution. The third parameter specifies the amount of time, in milliseconds, between subsequent executions. In the preceding example, you essentially print out the value of the counter every one second (1,000 milliseconds). The service repeatedly prints the value of counter until the service is terminated: @Override public void onDestroy() { super.onDestroy(); if (timer != null){ timer.cancel(); } Toast.makeText(this, “Service Destroyed”, Toast.LENGTH_LONG).show(); } For the scheduleAtFixedRate() method, your code is executed at fixed time intervals, regardless of how long each task takes. For example, if the code within your run() method takes two seconds to complete, then your second task will start immediately after the first task has ended. Similarly, if your delay is set to three seconds and the task takes two seconds to complete, then the second task will wait for one second before starting. Executing Asynchronous Tasks on Separate Threads Using IntentService Earlier in this chapter, you saw how to start a service using the startService() method and stop a service using the stopService() method. You have also seen how you should execute long-running task on a separate thread — not the same thread as the calling activities. It is important to note that once your service has finished executing a task, it should be stopped as soon as possible so that it does not unnecessarily hold up valuable resources. That’s why you use the stopSelf() method to stop the service when a task has been completed. Unfortunately, a lot of developers often forgot to terminate the service when it is done performing its task. To easily create a service that runs a task asynchro- nously and terminates itself when it is done, you can use the IntentService class.
- 366. 344 ❘ Chapter 10 Developing Android Services The IntentService class is a base class for Service that handles asynchronous requests on demand. It is started just like a normal service and it executes its task within a worker thread and terminates itself when the task is completed. The following Try It Out demonstrates how to use the IntentService class. Try It Out Using the IntentService Class to Auto-Stop a Service 1 . Using the same project created in the previous section, add a new class file named MyIntentService.java. . 2 Populate the MyIntentService.java file as follows: package net.learn2develop.Services; import java.net.MalformedURLException; import java.net.URL; import android.app.IntentService; import android.content.Intent; import android.util.Log; public class MyIntentService extends IntentService { public MyIntentService() { super(“MyIntentServiceName”); } @Override protected void onHandleIntent(Intent intent) { try { int result = DownloadFile(new URL(“http://www.amazon.com/somefile.pdf”)); Log.d(“IntentService”, “Downloaded “ + result + “ bytes”); } catch (MalformedURLException e) { e.printStackTrace(); } } private int DownloadFile(URL url) { try { //---simulate taking some time to download a file--- Thread.sleep(5000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } return 100; } } 3 . Add the following statement in bold to the AndroidManifest.xml file: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.Services” android:versionCode=”1”
- 367. Creating Your Own Services ❘ 345 android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> <service android:name=”.MyService” /> <service android:name=”.MyIntentService” /> </application> <uses-sdk android:minSdkVersion=”9” /> <uses-permission android:name=”android.permission.INTERNET”></uses-permission> </manifest> 4 . Add the following statement in bold to the MainActivity.java file: public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button btnStart = (Button) findViewById(R.id.btnStartService); btnStart.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //startService(new Intent(getBaseContext(), MyService.class)); startService(new Intent(getBaseContext(), MyIntentService.class)); } }); Button btnStop = (Button) findViewById(R.id.btnStopService); btnStop.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { stopService(new Intent(getBaseContext(), MyService.class)); } }); } } 5 . Press F11 to debug the application on the Android Emulator. 6. Click the Start Service button. After about five seconds, you should observe the following statement in the LogCat window: 01-17 03:05:21.244: DEBUG/IntentService(692): Downloaded 100 bytes How It Works First, you defined the MyIntentService class, which extends the IntentService class instead of the Service class: public class MyIntentService extends IntentService { ... }
- 368. 346 ❘ Chapter 10 Developing Android Services You needed to implement a constructor for the class and call its superclass with the name of the intent service (setting it with a string): public MyIntentService() { super(“MyIntentServiceName”); } You then implemented the onHandleIntent() method, which is executed on a worker thread: @Override protected void onHandleIntent(Intent intent) { try { int result = DownloadFile(new URL(“http://www.amazon.com/somefile.pdf”)); Log.d(“IntentService”, “Downloaded “ + result + “ bytes”); } catch (MalformedURLException e) { e.printStackTrace(); } } The onHandleIntent() method is where you place the code that needs to be executed on a separate thread, such as downloading a file from a server. When the code has finished executing, the thread is terminated and the service is stopped automatically. Communicating between a Service and an Activity Often a service simply executes in its own thread, independently of the activity that calls it. This doesn’t pose any problem if you simply want the service to perform some tasks periodically and the activity does not need to be notified of the status of the service. For example, you may have a service that periodically logs the geographical location of the device to a database. In this case, there is no need for your service to interact with any activities, because its main purpose is to save the coordinates into a database. However, suppose you want to monitor for a particular location. When the service logs an address that is near the location you are monitoring, it might need to communicate that information to the activity. In this case, you would need to devise a way for the service to interact with the activity. The following Try It Out demonstrates how a service can communicate with an activity using a BroadcastReceiver. Try It Out Invoking an Activity from a Service 1 . Using the same project created in the previous section, add the following statements in bold to the MyIntentService.java file: package net.learn2develop.Services; import java.net.MalformedURLException; import java.net.URL;
- 369. Communicating between a Service and an Activity ❘ 347 import android.app.IntentService; import android.content.Intent; import android.util.Log; public class MyIntentService extends IntentService { public MyIntentService() { super(“MyIntentServiceName”); } @Override protected void onHandleIntent(Intent intent) { try { int result = DownloadFile(new URL(“http://www.amazon.com/somefile.pdf”)); Log.d(“IntentService”, “Downloaded “ + result + “ bytes”); //---send a broadcast to inform the activity // that the file has been downloaded--- Intent broadcastIntent = new Intent(); broadcastIntent.setAction(“FILE_DOWNLOADED_ACTION”); getBaseContext().sendBroadcast(broadcastIntent); } catch (MalformedURLException e) { e.printStackTrace(); } } private int DownloadFile(URL url) { try { //---simulate taking some time to download a file--- Thread.sleep(5000); } catch (InterruptedException e) { e.printStackTrace(); } return 100; } } 2 . Add the following statements in bold to the MainActivity.java file: package net.learn2develop.Services; import android.app.Activity; import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.Toast; import android.content.IntentFilter; public class MainActivity extends Activity {
- 370. 348 ❘ Chapter 10 Developing Android Services IntentFilter intentFilter; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---intent to filter for file downloaded intent--- intentFilter = new IntentFilter(); intentFilter.addAction(“FILE_DOWNLOADED_ACTION”); //---register the receiver--- registerReceiver(intentReceiver, intentFilter); Button btnStart = (Button) findViewById(R.id.btnStartService); btnStart.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //startService(new Intent(getBaseContext(), MyService.class)); startService(new Intent(getBaseContext(), MyIntentService.class)); } }); Button btnStop = (Button) findViewById(R.id.btnStopService); btnStop.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { stopService(new Intent(getBaseContext(), MyService.class)); } }); } private BroadcastReceiver intentReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { Toast.makeText(getBaseContext(), “File downloaded!”, Toast.LENGTH_LONG).show(); } }; } 3 . Press F11 to debug the application on the Android Emulator. 4 . Click the Start Service button. After about five seconds, the Toast class will display a message indicating that the file has been downloaded (see Figure 10-5). How It Works To notify an activity when a service has finished its execution, you broadcast an intent using the sendBroadcast() method: @Override protected void onHandleIntent(Intent intent) { try { int result = DownloadFile(new URL(“http://www.amazon.com/somefile.pdf”));
- 371. Communicating between a Service and an Activity ❘ 349 Log.d(“IntentService”, “Downloaded “ + result + “ bytes”); //---send a broadcast to inform the activity // that the file has been downloaded--- Intent broadcastIntent = new Intent(); broadcastIntent.setAction(“FILE_DOWNLOADED_ACTION”); getBaseContext().sendBroadcast(broadcastIntent); } catch (MalformedURLException e) { e.printStackTrace(); } } The action of this intent that you are broadcasting is set to “FILE_DOWNLOADED_ACTION”, which means any activity that is listening for this intent will be invoked. Hence, in your MainActivity.java file, you listen for this intent using the registerReceiver() method from the IntentFilter class: @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //---intent to filter for file downloaded intent--- intentFilter = new IntentFilter(); intentFilter.addAction(“FILE_DOWNLOADED_ACTION”); //---register the receiver--- registerReceiver(intentReceiver, intentFilter); ... ... } Figure 10-5
- 372. 350 ❘ chApter 10 develoPinG android ServiceS When the intent is received, it invokes an instance of the BroadcastReceiver class that you have defined: privateBroadcastReceiverintentReceiver=newBroadcastReceiver(){ @Override publicvoidonReceive(Contextcontext,Intentintent){ Toast.makeText(getBaseContext(),“Filedownloaded!”, Toast.LENGTH_LONG).show(); } }; } NOTE Chapter 8 discusses the BroadcastReceiver class in more detail. In this case, you displayed the message “File downloaded!” Of course, if you need to pass some data from the service to the activity, you can make use of the Intent object. The next section discusses this. Binding ActivitieS to ServiceS So far, you have seen how services are created and how they are called and terminated when they are done with their task. All the services that you have seen are simple — either they start with a counter and increment at regular intervals, or they download a fi xed set of fi les from the Internet. However, real-world services are usually much more sophisticated, requiring the passing of data so that they can do the job correctly for you. Using the service demonstrated earlier that downloads a set of fi les, suppose you now want to let the Do calling activity determine what fi les to download, instead of hardcoding them in the service. Here is what you need to do. First, in the calling activity, you create an Intent object, specifying the service name: ButtonbtnStart=(Button)findViewById(R.id.btnStartService); btnStart.setOnClickListener(newView.OnClickListener(){ publicvoidonClick(Viewv){ Intent intent = new Intent(getBaseContext(), MyService.class); } }); You then create an array of URL objects and assign it to the Intent object through its putExtra() method. Finally, you start the service using the Intent object: ButtonbtnStart=(Button)findViewById(R.id.btnStartService); btnStart.setOnClickListener(newView.OnClickListener(){ publicvoidonClick(Viewv){ Intentintent=newIntent(getBaseContext(),MyService.class); try { URL[] urls = new URL[] {
- 373. Binding Activities to Services ❘ 351 new URL(“http://www.amazon.com/somefiles.pdf”), new URL(“http://www.wrox.com/somefiles.pdf”), new URL(“http://www.google.com/somefiles.pdf”), new URL(“http://www.learn2develop.net/somefiles.pdf”)}; intent.putExtra(“URLs”, urls); } catch (MalformedURLException e) { e.printStackTrace(); } startService(intent); } }); Note that the URL array is assigned to the Intent object as an Object array. On the service’s end, you need to extract the data passed in through the Intent object in the onStartCommand() method: @Override public int onStartCommand(Intent intent, int flags, int startId) { // We want this service to continue running until it is explicitly // stopped, so return sticky. Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show(); Object[] objUrls = (Object[]) intent.getExtras().get(“URLs”); URL[] urls = new URL[objUrls.length]; for (int i=0; i<objUrls.length-1; i++) { urls[i] = (URL) objUrls[i]; } new DoBackgroundTask().execute(urls); return START_STICKY; } The preceding first extracts the data using the getExtras() method to return a Bundle object. It then uses the get() method to extract out the URL array as an Object array. Because in Java you can- not directly cast an array from one type to another, you have to create a loop and cast each member of the array individually. Finally, you execute the background task by passing the URL array into the execute() method. This is one way in which your activity can pass values to the service. As you can see, if you have relatively complex data to pass to the service, you have to do some additional work to ensure that the data is passed correctly. A better way to pass data is to bind the activity directly to the service so that the activity can call any public members and methods on the service directly. The following Try It Out shows you how to bind an activity to a service. Try It Out Accessing Members of a Property Directly through Binding 1 . Using the same project created earlier, add the following statements in bold to the MyService.java file: package net.learn2develop.Services; import java.net.URL; import java.util.Timer;
- 374. 352 ❘ Chapter 10 Developing Android Services import java.util.TimerTask; import android.app.Service; import android.content.Intent; import android.os.AsyncTask; import android.util.Log; import android.widget.Toast; import android.os.IBinder; import android.os.Binder; public class MyService extends Service { int counter = 0; URL[] urls; static final int UPDATE_INTERVAL = 1000; private Timer timer = new Timer(); private final IBinder binder = new MyBinder(); public class MyBinder extends Binder { MyService getService() { return MyService.this; } } @Override public IBinder onBind(Intent arg0) { //return null; return binder; } @Override public int onStartCommand(Intent intent, int flags, int startId) { // We want this service to continue running until it is explicitly // stopped, so return sticky. Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show(); new DoBackgroundTask().execute(urls); return START_STICKY; } @Override public void onDestroy() { ... } private int DownloadFile(URL url) { ... } private class DoBackgroundTask extends AsyncTask<URL, Integer, Long> { ... } }
- 375. Binding Activities to Services ❘ 353 2 . In the MainActivity.java file, add the following statements in bold: package net.learn2develop.Services; import java.net.MalformedURLException; import java.net.URL; import android.app.Activity; import android.content.BroadcastReceiver; import android.content.ComponentName; import android.content.Context; import android.content.Intent; import android.content.IntentFilter; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.Toast; import android.os.IBinder; import android.content.ServiceConnection; public class MainActivity extends Activity { IntentFilter intentFilter; private MyService serviceBinder; Intent i; private ServiceConnection connection = new ServiceConnection() { public void onServiceConnected(ComponentName className, IBinder service) { //---called when the connection is made--- serviceBinder = ((MyService.MyBinder)service).getService(); try { URL[] urls = new URL[] { new URL(“http://www.amazon.com/somefiles.pdf”), new URL(“http://www.wrox.com/somefiles.pdf”), new URL(“http://www.google.com/somefiles.pdf”), new URL(“http://www.learn2develop.net/somefiles.pdf”)}; //---assign the URLs to the service through the serviceBinder object--- serviceBinder.urls = urls; } catch (MalformedURLException e) { e.printStackTrace(); } startService(i); } public void onServiceDisconnected(ComponentName className) { //---called when the service disconnects--- serviceBinder = null; } }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
- 376. 354 ❘ Chapter 10 Developing Android Services setContentView(R.layout.main); //---intent to filter for file downloaded intent--- intentFilter = new IntentFilter(); intentFilter.addAction(“FILE_DOWNLOADED_ACTION”); //---register the receiver--- registerReceiver(intentReceiver, intentFilter); Button btnStart = (Button) findViewById(R.id.btnStartService); btnStart.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { i = new Intent(MainActivity.this, MyService.class); bindService(i, connection, Context.BIND_AUTO_CREATE); } }); Button btnStop = (Button) findViewById(R.id.btnStopService); btnStop.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { stopService(new Intent(getBaseContext(), MyService.class)); } }); } private BroadcastReceiver intentReceiver = new BroadcastReceiver() { ... }; } 3 . Press F11 to debug the application. Clicking the Start Service button will start the service as normal. How It Works To bind activities to a service, you must first declare an inner class in your service that extends the Binder class: public class MyBinder extends Binder { MyService getService() { return MyService.this; } } Within this class you implemented the getService() method, which returns an instance of the service. You then created an instance of the MyBinder class: private final IBinder binder = new MyBinder(); You also modified the onBind() method to return the MyBinder instance: @Override public IBinder onBind(Intent arg0) { //return null; return binder; }
- 377. Binding Activities to Services ❘ 355 In the onStartCommand() method, you then call the execute() method using the urls array, which you declared as a public member in your service: public class MyService extends Service { int counter = 0; URL[] urls; ... ... ... @Override public int onStartCommand(Intent intent, int flags, int startId) { // We want this service to continue running until it is explicitly // stopped, so return sticky. Toast.makeText(this, “Service Started”, Toast.LENGTH_LONG).show(); new DoBackgroundTask().execute(urls); return START_STICKY; } This URL array can be set directly from your activity, which you did next. In the MainActivity.java file, you first declared an instance of your service and an Intent object: private MyService serviceBinder; Intent i; The serviceBinder object will be used as a reference to the service, which you accessed directly. You then created an instance of the ServiceConnection class so that you could monitor the state of the service: private ServiceConnection connection = new ServiceConnection() { public void onServiceConnected(ComponentName className, IBinder service) { //---called when the connection is made--- serviceBinder = ((MyService.MyBinder)service).getService(); try { URL[] urls = new URL[] { new URL(“http://www.amazon.com/somefiles.pdf”), new URL(“http://www.wrox.com/somefiles.pdf”), new URL(“http://www.google.com/somefiles.pdf”), new URL(“http://www.learn2develop.net/somefiles.pdf”)}; //---assign the URLs to the service through the serviceBinder object--- serviceBinder.urls = urls; } catch (MalformedURLException e) { e.printStackTrace(); } startService(i); } public void onServiceDisconnected(ComponentName className) { //---called when the service disconnects--- serviceBinder = null; } };
- 378. 356 ❘ Chapter 10 Developing Android Services You need to implement two methods: onServiceConnected() and onServiceDisconnected(). The onServiceConnected() method is called when the activity is connected to the service; the onServiceDisconnected()method is called when the service is disconnected from the activity. In the onServiceConnected() method, when the activity is connected to the service, you obtained an instance of the service by using the getService() method of the service argument and then assigning it to the serviceBinder object. The serviceBinder object is a reference to the service, and all the mem- bers and methods in the service can be accessed through this object. Here, you created an URL array and then directly assigned it to the public member in the service: URL[] urls = new URL[] { new URL(“http://www.amazon.com/somefiles.pdf”), new URL(“http://www.wrox.com/somefiles.pdf”), new URL(“http://www.google.com/somefiles.pdf”), new URL(“http://www.learn2develop.net/somefiles.pdf”)}; //---assign the URLs to the service through the serviceBinder object--- serviceBinder.urls = urls; You then started the service using an Intent object: startService(i); Before you can start the service, you have to bind the activity to the service. This you did in the onClick() method of the Start Service button: Button btnStart = (Button) findViewById(R.id.btnStartService); btnStart.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { i = new Intent(MainActivity.this, MyService.class); bindService(i, connection, Context.BIND_AUTO_CREATE); } }); The bindService() method enables your activity to be connected to the service. It takes three arguments: an Intent object, a ServiceConnection object, and a flag to indicate how the service should be bound. Summary In this chapter, you learned how to create a service in your Android project to execute long-running tasks. You have seen the many approaches you can use to ensure that the background task is exe- cuted in an asynchronous fashion, without tying up the main calling activity. You have also learned how an activity can pass data into a service, and how you can alternatively bind to an activity so that it can access a service more directly.
- 379. Summary ❘ 357 Exercises 1 . Why is it important to put long-running code in a service on a separate thread? 2 . What is the use of the IntentService class? 3. Name the three methods you need to implement in an AsyncTask class. 4. How can a service notify an activity of an event happening? Answers to Exercises can be found in Appendix C.
- 380. 358 ❘ Chapter 10 Developing Android Services ⊲⊲ What You Learned In This Chapter Topic Key Concepts Creating a service Create a class and extend the Service class. Implementing the methods Implement the following methods: onBind(), onStartCommand(), in a service and onDestroy(). Starting a service Use the startService() method. Stopping a service Use the stopService() method. Performing long-running Use the AsyncTask class and implement three methods: tasks doInBackground(), onProgressUpdate(), and onPostExecute(). Performing repeated tasks Use the Timer class and call its scheduleAtFixedRate() method. Executing tasks on a separate Use the IntentService class. thread and auto-stopping a service Communicating between an Use the Intent object to pass data into the service. For a service, activity and a service broadcast an Intent to notify an activity. Binding an activity to a Use the Binder class in your service and implement the service ServiceConnection class in your calling activity.
- 381. 11 Publishing Android Applications WhAt you Will leArn in thiS chApter ➤➤ How to prepare your application for deployment ➤➤ How to export your application as an APK file and sign it with a new certificate ➤➤ How to distribute your Android application ➤➤ How to publish your application on the Android Market So far you have seen quite a lot of interesting things you can do with Android. However, in order to get your application running on users’ devices, you need a way to deploy it and dis- tribute it. In this chapter, you will learn how to prepare your Android applications for deploy- ment and get them onto your customer’s devices. In addition, you will learn how to publish your applications on the Android Market, where you can sell them and make some money! prepAring For puBliShing Google has made it relatively easy to publish your Android application so that it can be quickly distributed to end users. The steps to publishing your Android application generally involve the following: 1 . Export your application as an APK (Android Package) file. 2 . Generate your own self-signed certificate and digitally sign your application with it. 3 . Deploy the signed application. 4 . Use the Android Market for hosting and selling your application.
- 382. 360 ❘ Chapter 11 Publishing Android Applications In the following sections, you will learn how to prepare your application for signing, and then learn about the various ways to deploy your applications. This chapter uses the LBS project created in Chapter 9 to demonstrate how to deploy an Android application. Versioning Beginning with version 1.0 of the Android SDK, the AndroidManifest.xml file of every Android application includes the android:versionCode and android:versionName attributes: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.LBS” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”@string/app_name”> <uses-library android:name=”com.google.android.maps” /> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”7” /> <uses-permission android:name=”android.permission.INTERNET” /> <uses-permission android:name=”android.permission.ACCESS_FINE_LOCATION” /> <uses-permission android:name=”android.permission.ACCESS_COARSE_LOCATION” /> </manifest> The android:versionCode attribute represents the version number of your application. For every revi- sion you make to the application, you should increment this value by 1 so that you can programmatically differentiate the newest version from the previous one. This value is never used by the Android system, but is useful for developers as a means to obtain the version number of an application. However, the android:versionCode attribute is used by Android Market to determine if there is a newer version of your application available. You can programmatically retrieve the value of the android:versionCode attribute by using the getPackageInfo() method from the PackageManager class, like this: PackageManager pm = getPackageManager(); try { //---get the package info--- PackageInfo pi = pm.getPackageInfo(“net.learn2develop.LBS”, 0); //---display the versioncode--- Toast.makeText(getBaseContext(), “VersionCode: “ +Integer.toString(pi.versionCode), Toast.LENGTH_SHORT).show();
- 383. Preparing for Publishing ❘ 361 } catch (NameNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } The android:versionName attribute contains versioning information that is visible to the users. It should contain values in the format: <major>.<minor>.<point>. If your application undergoes a major upgrade, you should increase the <major> by 1. For small incremental updates, you can either increase the <minor> or <point> by 1. For example, a new application may have a version name of “1.0.0”. For a small incremental update, you might change to “1.1.0” or “1.0.1”. For the next major update, you might change it “2.0.0”. If you are planning to publish your application on the Android Market (www.android.com/market/), the AndroidManifest.xml file must have the following attributes: ➤➤ android:versionCode (within the <manifest> element) ➤➤ android:versionName (within the <manifest> element) ➤➤ android:icon (within the <application> element) ➤➤ android:label (within the <application> element) The android:label attribute specifies the name of your application. This name will be displayed in the Settings ➪ Applications ➪ Manage Applications section of your Android device. For the LBS project, we’ll give the application the name “Where Am I”: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android” package=”net.learn2develop.LBS” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”Where Am I”> <uses-library android:name=”com.google.android.maps” /> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”7” /> <uses-permission android:name=”android.permission.INTERNET” /> <uses-permission android:name=”android.permission.ACCESS_FINE_LOCATION” /> <uses-permission android:name=”android.permission.ACCESS_COARSE_LOCATION” /> </manifest> In addition, if your application needs a minimum version of the SDK, you can specify it in the AndroidManifest.xml file using the <uses-sdk> element: <?xml version=”1.0” encoding=”utf-8”?> <manifest xmlns:android=”http://schemas.android.com/apk/res/android”
- 384. 362 ❘ Chapter 11 Publishing Android Applications package=”net.learn2develop.LBS” android:versionCode=”1” android:versionName=”1.0”> <application android:icon=”@drawable/icon” android:label=”Where Am I”> <uses-library android:name=”com.google.android.maps” /> <activity android:name=”.MainActivity” android:label=”@string/app_name”> <intent-filter> <action android:name=”android.intent.action.MAIN” /> <category android:name=”android.intent.category.LAUNCHER” /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion=”7” /> <uses-permission android:name=”android.permission.INTERNET” /> <uses-permission android:name=”android.permission.ACCESS_FINE_LOCATION” /> <uses-permission android:name=”android.permission.ACCESS_COARSE_LOCATION” /> </manifest> In the preceding example, the application requires a minimum of SDK version 7, which is Android 2.1. In general, it is always good to set this version number to the lowest one that your application can sup- port. This ensures that a wider range of users will be able to run your application. Although the latest version of Android at the time of writing is 2.3, a lot of devices are still running Android 2.1 and 2.2. Digitally Signing Your Android Applications All Android applications must be digitally signed before they are allowed to be deployed onto a device (or emulator). Unlike some mobile platforms, you need not purchase digital certificates from a certifi- cate authority (CA) to sign your applications. Instead, you can generate your own self-signed certificate and use it to sign your Android applications. When you use Eclipse to develop your Android application and then press F11 to deploy it to an emu- lator, Eclipse automatically signs it for you. You can verify this by going to Windows ➪ Preferences in Eclipse, expanding the Android item, and selecting Build (see Figure 11-1). Eclipse uses a default debug keystore (appropriately named “debug.keystore”) to sign your application. A keystore is com- monly known as a digital certificate. If you are publishing an Android application, you must sign it with your own certificate. Applications signed with the debug certificate cannot be published. While you can manually generate your own certificates using the keytool.exe utility provided by the Java SDK, Eclipse has made it easy for you by including a wizard that walks you through the steps to generate a certificate. It will also sign your application with the generated certificate (which you can also sign manually using the jarsigner.exe tool from the Java SDK). The following Try It Out demonstrates how to use Eclipse to export an Android application and sign it with a newly generated certificate.
- 385. Preparing for Publishing ❘ 363 Figure 11-1 Try It Out Exporting and Signing an Android Application 1 . Using Eclipse, open the LBS projected created in Chapter 9. . 2 Select the LBS project in Eclipse and then select File ➪ Export…. 3 . In the Export dialog, expand the Android item and select Export Android Application (see Figure 11-2). Click Next. Figure 11-2
- 386. 364 ❘ Chapter 11 Publishing Android Applications 4 . The LBS project should now be displayed (see Figure 11-3). Click Next. 5. Select the “Create new keystore” option to create a new certificate (keystore) for signing your appli- cation (see Figure 11-4). Enter a path to save your new keystore and then enter a password to pro- tect the keystore. For this example, type in “password” as the password. Click Next. 6. Provide an alias for the private key (name it DistributionKeyStoreAlias; see Figure 11-5) and enter a password to protect the private key. For this example, enter “password” as the password. You also need to enter a validity period for the key. According to Google, your application must be signed with a cryptographic private key whose validity period ends after October 2033. Hence, enter a 22 number that is greater than 2033 minus the current year. Click Next. 7. Enter a path to store the destination APK file (see Figure 11-6). Click Finish. The APK file will now be generated. 8 . Recall from Chapter 9 that the LBS application requires the use of the Google Maps API key, which you applied by using your debug.keystore’s MD5 fingerprint. This means that the Google Maps API key is essentially tied to the debug.keystore used to sign your application. Because you are now generating your new keystore to sign your application for deployment, you need to apply for the Google Maps API key again, using the new keystore’s MD5 fingerprint. To do so, go to the com- mand prompt and enter the following command (the location of your keytool.exe utility might differ slightly and you would need to replace the path of the keystore with the path you selected earlier in step 5; see also Figure 11-7): C:Program FilesJavajre6bin>keytool.exe -list -alias DistributionKeyStoreAlias -keystore “C:UsersWei-Meng LeeDesktopDistributionKeyStore” -storepass password -keypass password Figure 11-3 Figure 11-4
- 387. Preparing for Publishing ❘ 365 Figure 11-5 Figure 11-6 9 . Using the MD5 fingerprint obtained from the previous step, go to http://code.google.com/ android/add-ons/google-apis/maps-api-signup.html and sign up for a new Maps API key. 0. Enter the new Maps API key in the main.xml file: 1 <?xml version=”1.0” encoding=”utf-8”?> <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android” android:orientation=”vertical” android:layout_width=”fill_parent” android:layout_height=”fill_parent” > <com.google.android.maps.MapView android:id=”@+id/mapView” android:layout_width=”fill_parent” android:layout_height=”fill_parent” android:enabled=”true” android:clickable=”true” android:apiKey=”<Your Key Here>” /> </LinearLayout> Figure 11-7 1 1. With the new Maps API key entered in the main.xml file, you now need to export the application once more and re-sign it. Repeat steps 2 through 4. When you are asked to select a keystore,
- 388. 366 ❘ Chapter 11 Publishing Android Applications select the “Use existing keystore” option (see Figure 11-8) and enter the password you used earlier to protect your keystore (in this case, “password”). Click Next. 1 2. Select the “Use existing key” option (see Figure 11-9) and enter the password you set earlier to secure the private key (enter “password”). Click Next. 13. Click Finish (see Figure 11-10) to generate the APK file again. That’s it! The APK is now generated and it con- tains the new Map API key that is tied to the new keystore. How It Works Eclipse provides the Export Android Application option, which helps you to both export your Figure 11-8 Android application as an APK file and generate a new keystore to sign the APK file. For applications that use the Maps API key, note that the Maps API key must be associated with the new keystore that you use to sign your APK file. Figure 11-9 Figure 11-10
- 389. Deploying APK Files ❘ 367 deploying Apk FileS Once you have signed your APK fi les, you need a way to get them onto your users’ devices. The fol- lowing sections describe the various ways to deploy your APK fi les. Three methods are covered: ➤➤ Deploying manually using the adb.exe tool ➤➤ Hosting the application on a web server ➤➤ Publishing through the Android Market Besides the above methods, you can install your applications on users’ devices through e-mails, SD card, etc. As long as you can transfer the APK file onto the user’s device, you can install the application. using the adb .exe tool Once your Android application is signed, you can deploy it to emulators and devices using the adb.exe (Android Debug Bridge) tool (located in the platform-tools folder of the Android SDK). Using the command prompt in Windows, navigate to the “<Android_SDK>platform-tools” folder. To install the application to an emulator/device (assuming the emulator is currently up and running or a device is currently connected), issue the following command: adb install “C:UsersWei-Meng LeeDesktopLBS.apk” exploring the AdB .exe tool The adb.exe tool is a very versatile tool that enables you to control Android devices (and emulators) connected to your computer. By default, when you use the adb command, it assumes that currently there is only one connected device/emulator. If you have more than one device connected, the adb command returns an error message: error:morethanonedeviceandemulator You can view the devices currently connected to your computer by using the devices option with adb, like this: D:Android2.3android-sdk-windowsplatform-tools>adbdevices Listofdevicesattached HT07YPY09335device emulator-5554device emulator-5556device As the preceding example shows, this returns the list of devices currently attached. To issue a command for a particular device, you need to indicate the device using the -s option, like this: adb–semulator-5556installLBS.apk continues
- 390. 368 ❘ chApter 11 PUBliShinG android aPPlicationS (continued) If you try to install an APK fi le onto a device that already has the APK fi le, it will display the following error message: Failure[INSTALL_FAILED_ALREADY_EXISTS] Figure 11-11 shows an APK fi le successfully installed onto a real device. Figure 11-11 When you inspect the Launcher on the Android device/emulator, you will be able to see the LBS icon (on the left of Figure 11-12). If you select Settings➪ Applications➪ Manage Applications on your Android device/emulator, you will see the “Where Am I” application (on the right in Figure 11-12). Figure 11-12 Besides using the adb.exe tool to install applications, you can also use it to remove an installed appli- cation. To do so, you can use the shell option to remove an application from its installed folder: adb shell rm /data/app/net.learn2develop.LBS.apk Another way to deploy an application is to use the DDMS tool in Eclipse (see Figure 11-13). With an emulator (or device) selected, use the File Explorer in DDMS to go to the /data/app folder and use the “Push a fi le onto the device” button to copy the APK fi le onto the device.
- 391. Deploying APK Files ❘ 369 Figure 11-13 using a Web Server If you wish to host your application on your own, you can use a web server to do that. This is ideal if you have your own web hosting services and want to provide the application free of charge to your users (or you can restrict access to certain groups of people). NOTE Even if you restrict your application to a certain group of people, there is nothing to stop users from redistributing your application to other users after they have downloaded your APK file. To demonstrate this, I will use the Internet Information Server (IIS) on my Windows 7 computer. Copy the signed LBS.apk fi le to c:inetpubwwwroot. In addition, create a new HTML fi le named Install.html with the following content: <html> <title>WhereAmIapplication</title> Do <body> DownloadtheWhereAmIapplication<ahref=”LBS.apk”>here</a> </body> </html> NOTE If you are unsure how to set up the IIS on your Windows 7 computer, check out the following link: http://technet.microsoft.com/en-us/library/ cc725762.aspx. On your web server, you may need to register a new MIME type for the APK fi le. The MIME type for the .apk extension is application/vnd.android.package-archive. NOTE To install APK files over the Web, you need an SD card installed on your emulator or device. This is because the downloaded APK files will be saved to the download folder created on the SD card.
- 392. 370 ❘ Chapter 11 Publishing Android Applications By default, for online installation of Android applications, the Android Emulator or device only allows applications to be installed from the Android Market (www.android.com/market/). Hence, for installation over a web server, you need to configure your Android Emulator/device to accept appli- cations from non-Market sources. From the Application settings menu, check the “Unknown sources” item (see Figure 11-14). You will be prompted with a warning message. Click OK. Checking this item will allow the Emulator/device to install applications from other non-Market sources (such as from a web server). Figure 11-14 To install the LBS.apk application from the IIS web server running on your computer, launch the Browser application on the Android Emulator/device and navigate to the URL pointing to the APK file. To refer to the computer running the emulator, you should use the special IP address of 10.0.2.2. Alternatively, you can also use the IP address of the host computer. Figure 11-15 shows the Install .html file loaded on the web browser. Clicking the “here” link will download the APK file onto your device. Drag the notification bar down to reveal the download status. To install the downloaded application, simply tap on it and it will show the permission(s) required by this application (see Figure 11-16). Click the Install button to proceed with the installation. When the application is installed, you can launch it by clicking the Open button (see Figure 11-17). Besides using a web server, you can also e‑mail your application to users as an attachment; when the users receive the e‑mail they can download the attachment and install the application directly onto their device.
- 393. Deploying APK Files ❘ 371 Figure 11-15 Figure 11-16
- 394. 372 ❘ Chapter 11 Publishing Android Applications Figure 11-17 Publishing on the Android Market So far, you have learned how to package your Android application and distribute it in various ways — via web server, the adb.exe file, e‑mail, SD card, and so on. However, these methods do not provide a way for users to discover your applications easily. A better way is to host your application on the Android Market, a Google-hosted service that makes it very easy for users to discover and download (i.e., purchase) applications for their Android devices. Users simply need to launch the Market application on their Android device in order to discover a wide range of applications that they can install on their devices. In this section, you will learn how to publish your Android application on the Android Market. I will walk you through each of the steps involved, including the various items you need to prepare for your application for submission to the Android Market. Creating a Developer Profile The first step toward publishing on the Android Market is to create a developer profile at http://market .android.com/publish/Home. For this, you need a Google account (such as your Gmail account). Once you have logged in to the Android Market, you first create your developer profile (see Figure 11-18). Click Continue after entering the required information. For publishing on the Android Market, you need to pay a one-time registration fee, currently U.S.$25. Click the Google Checkout button (see Figure 11-19) to be redirected to a page where you can pay the registration fee. After paying, click the Continue link.
- 395. Deploying APK Files ❘ 373 Next, you need to agree to the Android Market Developer Distribution Agreement. Check the “I agree” checkbox and click the “I agree. Continue” link (see Figure 11-20). Figure 11-18 Figure 11-19 Submitting Your Apps Once you have set up your profile, you are ready to submit your application to the Android Market. If you intend to charge for your application, click the Setup Merchant Account link located at the bottom of the screen. Here you enter additional information such as bank account and tax ID.
- 396. 374 ❘ Chapter 11 Publishing Android Applications For free applications, click the Upload Application link, shown in Figure 11-21. Figure 11-20 Figure 11-21
- 397. Deploying APK Files ❘ 375 You will be asked to supply some details for your application. Figure 11-22 shows the first set of details you need to provide. Among the information needed, the following are compulsory: ➤➤ The application in APK format ➤➤ At least two screenshots. You can use the DDMS perspective in Eclipse to capture screenshots of your application running on the Emulator or real device. ➤➤ A high-resolution application icon. This size of this image must be 512×512 pixels. The other information details are optional, and you can always supply them later. Figure 11-22 Figure 11-23 shows that I have uploaded the LBS.apk file to the Android Market site. In particular, note that based on the APK file that you have uploaded, the user will be warned about any specific permis- sions required, and your application’s features will be used to filter search results. For example, because my application requires GPS access, it will not appear in the search result list if a user searches for my application on a device that does not have a GPS receiver. The next set of information you need to supply, shown in Figure 11-24, includes the title of your appli- cation, its description, as well as recent changes’ details (useful for application updates). You can also select the application type and the category in which it will appear in the Android Market. On the last dialog, you indicate whether your application employs copy protection, and specify a content rating. You also supply your website URL and your contact information (see Figure 11-25).
- 398. 376 ❘ Chapter 11 Publishing Android Applications When you have given your consent to the two guidelines and agreements, click Publish to publish your application on the Android Market. Figure 11-23 Figure 11-24
- 399. Deploying APK Files ❘ 377 That’s it! Your application is now available on the Android Market. You will be able to monitor any comments submitted about your application (see Figure 11-26), as well as bug reports and total number of downloads. Figure 11-25 Figure 11-26
- 400. 378 ❘ Chapter 11 Publishing Android Applications Good luck! All you need to do now is wait for the good news; and hopefully you can laugh your way to the bank soon! Summary In this chapter, you have seen how you can export your Android application as an APK file and then digitally sign it with a keystore created by yourself. You then learned about the various ways you can distribute your application, and the advantages of each method. Finally, you walked through the steps required to publish on the Android Market, which makes it possible for you to sell your appli- cation and reach out to a wider audience. Hopefully, this exposure enables you to sell a lot of copies and thereby make some decent money! Exercises 1 . How do you specify the minimum version of Android required by your application? 2 . How do you generate a self-sign certificate for signing your Android application? 3. How do you configure your Android device to accept applications from non-Market sources? Answers to Exercises can be found in Appendix C.
- 401. Summary ❘ 379 ⊲⊲ What You Learned In This Chapter Topic Key Concepts Checklist for publishing To publish an application on the Android Market, an application must your apps have the four required attributes in the AndroidManifest.xml file: android:versionCode, android:versionName , android:icon, and android:label. Applications must be All applications to be distributed must be signed with a self-signed signed certificate. The debug keystore is not valid for distribution. Exporting an application Use the Export feature of Eclipse to export the application as an APK and signing it file and then sign it with a self-signed certificate. Deploying APK files You can deploy using various means – web server, e-mail, adb.exe, DDMS, etc. Publishing your appli- Apply for the Android Market with a one-time fee of US$25 and you cation on the Android will be able to sell and host your apps on the Android Market. Market
- 403. A Using eclipse for Android Development Although Google supports the development of Android applications using IDEs such as IntelliJ, or basic editors like Emacs, Google’s recommendation is to use the Eclipse IDE together with the ADT Plugin. Doing so makes developing Android applications much easier and more pro- ductive. This appendix describes some of the neat features available in Eclipse that can make your development life much easier. NOTE If you have not downloaded Eclipse yet, please start with Chapter 1, where you will learn how to obtain Eclipse and configure it to work with the Android SDK. This appendix assumes that you have already set up your Eclipse environment for Android development. getting Around in eclipSe Eclipse is a highly extensible multi-language software development environment that supports application development of all sorts. Using Eclipse, you could write and test your applications using a wide variety of languages, such as Java, C, C++, PHP, Ruby, and so on. Because of its extensibility, new users of Eclipse often feel inundated with the IDE. Hence, the following sec- tions aim to make you more at home with Eclipse when you develop your Android applications. Workspaces Eclipse adopts the concept of a workspace. A workspace is a folder that you have chosen to store all your projects. When you fi rst start Eclipse, you are prompted to select a workspace (see Figure A-1).
- 404. 382 ❘ Appendix A Using Eclipse for Android Development Figure A-1 When Eclipse has finished launching the projects located in your workspace, it will display several panes in the IDE (see Figure A-2). Do Figure A-2 The following sections highlight some of the more important panes that you need to know about when developing Android applications. Package Explorer The Package Explorer, shown in Figure A-3, lists all the projects currently in your workspace. To edit a particular item in your project, you can double-click on it and the file will be displayed in the respective editor. You can also right-click on each item displayed in the Package Explorer to display context sensitive menu(s) related to the selected item. For example, if you wish to add a new .java file to the project, you can right- click on the package name in the Package Explorer and then select New ➪ Class (see Figure A-4).
- 405. Getting Around in Eclipse ❘ 383 Figure A-3 Figure A-4 Using Projects from Other Workspaces There may be times when you have several workspaces created to store different projects. If you need to access the project in another workspace, there are generally two ways to go about doing so. First, you can switch to the desired workspace by selecting File ➪ Switch Workspace (see Figure A-5). Specify the new workspace to work on and then restart Eclipse.
- 406. 384 ❘ Appendix A Using Eclipse for Android Development The second method is to import the project from another workspace into the current one. To do so, select File ➪ Import… and then select General ➪ Existing Projects into Workspace (see Figure A-6). In the Select root directory textbox, enter the path of the workspace containing the project(s) you want to import and tick the project(s) you want to import (see Figure A-7). To import the selected project(s), click Finish. Figure A-5 Figure A-6 Figure A-7
- 407. Getting Around in Eclipse ❘ 385 Note that even when you import a project from another workspace into the current workspace, the physical location of the imported project remains unchanged. That is, it will still be located in its original directory. To have a copy of the project in the current workspace, check the “Copy projects into workspace” option. Editors Depending on the type of items you have double-clicked in the Package Explorer, Eclipse will open the appropriate editor for you to edit the file. For example, if you double-click on a .java file, the text editor for editing the source file will be opened (see Figure A-8). Figure A-8 If you double-click on the icon.png file in the res/drawable- mdpi folder, the Windows Photo Viewer application will be invoked to display the image (see Figure A-9). Figure A-9
- 408. 386 ❘ Appendix A Using Eclipse for Android Development If you double-click on the main.xml file in the res/layout folder, Eclipse will display the UI editor, where you can graphically view and build the layout of your UI (see Figure A-10). Figure A-10 To edit the UI manually using XML, you can switch to XML view by clicking on the main.xml tab located at the bottom of the screen (see Figure A-11). Figure A-11
- 409. Getting Around in Eclipse ❘ 387 Perspectives In Eclipse, a perspective is a visual container for a set of views and editors. When you edit your project in Eclipse, you are in the Java perspective (see Figure A-12). The Java EE perspective is used for developing enterprise Java applications, and it includes other modules that are relevant to it. Figure A-12 You can switch to other perspectives by clicking on the per- spective name. If the perspective name is not shown, you can click the Open Perspective button and add a new perspective (see Figure A-13). The DDMS perspective contains the tools for communicating with Android emulators and devices. This is covered in more detail in Appendix B. The Debug perspective contains panes used for debugging your Android applications. You will learn more about this later in this appendix. Figure A-13 Auto Import of Namespaces The various classes in the Android library are organized into namespaces. As such, when you use a particular class from a namespace, you need to import the appropriate namespaces, like this: import android.app.Activity; import android.os.Bundle; Because the number of classes in the Android Library is very large, remembering the correct namespace for each class is not an easy task. Fortunately, Eclipse can help find the correct namespace for you, enabling you to import it with just a click. Figure A-14 shows that I have declared an object of type Button. Because I did not import the correct namespace for the Button class, Eclipse signals an error beneath the statement. When you move the mouse over the Button class, Eclipse displays a list of suggested fixes. In this case, I need to import the android .widget.Button namespace. Clicking the “Import ‘Button’ (android.widget)” link will add the import statement at the top of the file. Figure A-14 Alternatively, you can also use the following key combination: Control+Shift+o. This key combination will cause Eclipse to automatically import all the namespaces required by your class.
- 410. 388 ❘ Appendix A Using Eclipse for Android Development Code Completion Another very useful feature of Eclipse is the support for code completion. Code completion displays a context-sensitive list of relevant classes, objects, methods, and property names as you type in the code editor. For example, Figure A-15 shows code-completion in action. As I type the word “fin,” I can activate the code-completion feature by pressing Ctrl+Space. This will bring up a list of names that begin with “fin.” To select the required name, simply double-click on it or use your cursor to highlight it and press the Enter key. Code completion also works when you type a “.” after an object/class name. Figure A-16 shows an example. Figure A-15 Figure A-16 Refactoring Refactoring is a very useful feature that most mod- ern IDEs support. Eclipse supports a whole slew of refactoring features that make application develop- ment efficient. In Eclipse, when you position the cursor at a par- ticular object/variable, the editor will highlight all occurrences of the selected object in the current source (see Figure A-17). Figure A-17 This feature is very useful for identifying where a particular object is used in your code. To change the name of an object, simply right-click on it and select Refactor ➪ Rename… (see Figure A-18). After entering a new name for the object, all occurrences of the object will be changed dynamically (see Figure A-19). A detailed discussion of refactoring is beyond the scope of this book. For more information on refac- toring in Eclipse, refer to www.ibm.com/developerworks/library/os-ecref/.
- 411. Debugging ❘ 389 Figure A-18 Figure A-19 Debugging Eclipse supports debugging your application on both the Android Emulators as well as on real Android devices. When you press F11 in Eclipse, Eclipse will first determine whether an Android Emulator instance is already running or a real device is connected. If at least one emulator (or device) is running, Eclipse will deploy the application onto the running emulator or the connected device. If there is no emulator run- ning and no connected device, Eclipse will automatically launch an instance of the Android Emulator and deploy the application onto it. If you have more than one emulator or device connected, Eclipse will prompt you to select the target emulator/device on which to deploy the application (see Figure A-20). Select the target device you want to use and click OK. If you want to launch a new emulator instance to test the application, select Window ➪ Android SDK and AVD Manager to launch the AVD manager. Setting Breakpoints Setting breakpoints is a good way to temporarily pause the execution of the application and then examine the content of variables and objects. To set a breakpoint, double-click on the leftmost column in the code editor. Figure A-21 shows a break- point set on a particular statement.
- 412. 390 ❘ Appendix A Using Eclipse for Android Development Figure A-20 When the application is running and the first breakpoint is reached, Eclipse will display a Confirm Perspective Switch dialog. Basically, it wants to switch to the Debug perspective. To prevent this window from appearing again, check the “Remember my decision” checkbox Figure A-21 at the bottom and click Yes. Eclipse now highlights the breakpoint (see Figure A-22). At this point, you can right-click on any selected object/variable and view its content using the vari- ous options (Watch, Inspect, and Display) shown in Figure A-23. Figure A-24 shows the Inspect option displaying the content of the str variable. There are several options at this point to continue the execution: ➤➤ Step Into — Press F5 to step into the next method call/statement. ➤➤ Step Over — Press F6 to step over the next method call without entering it. ➤➤ Step Return — Press F7 to return from a method that has been stepped into. ➤➤ Resume Execution — Press F8 to resume the execution. Exceptions As you develop in Android, you will encounter numerous run-time exceptions that prevent your pro- gram from continuing. Examples of run-time exceptions include the following: ➤➤ Null reference exception (accessing an object which is null) ➤➤ Failure to specify the required permissions required by your application ➤➤ Arithmetic operation exceptions
- 413. Debugging ❘ 391 Figure A-22 Figure A-23 Figure A-24 Figure A-25 shows the current state of an application when an exception occurred. In this example, I am trying to send an SMS message from my application and it crashes when the SMS message is about to be sent.
- 414. 392 ❘ Appendix A Using Eclipse for Android Development Figure A-25 The various windows do not really identify the cause of the exception. To find out more, press F6 in Eclipse so that it can step over the current statement. The Variables window, shown in Figure A-26, indicates the cause of the exception. In this case, the SEND_SMS permission is missing. Figure A-26 To remedy this, all you need to do is to add the following permission statement in the AndroidManifest.xml file: <uses-permission android:name=”android.permission.SEND_SMS”/>
- 415. B Using the Android emulator The Android Emulator ships with the Android SDK and is an invaluable tool to help test your application without requiring you to purchase a real device. While you should thoroughly test your applications on real devices before you deploy them, the emulator mimics most of the capabilities of real devices. It is a very handy tool that you should make use of during the devel- opment stage of your project. This appendix provides some common tips and tricks for master- ing the Android Emulator. uSeS oF the Android emulAtor As discussed in Chapter 1, you can use the Android Emulator to emulate the different Android configurations by creating Android Virtual Devices (AVDs). You launch the Android Emulator by directly starting the AVD you have created in the Android SDK and AVD Manager window (see Figure B-1). Simply select the AVD and click the Start button. You have the option to scale the emulator to a particular size and monitor DPI. Alternatively, when you run an Android project in Eclipse, the Android Emulator is automati- cally invoked to test your application. You can customize the Android Emulator for each of your Android projects in Eclipse. To do so, simply select Run ➪ Run Configurations. Select the project name listed under Android Application on the left (see Figure B-2), and on the right you will see the Target tab. You can choose which AVD to use for testing your application, as well as emulate different scenarios, such as network speed and network latency. inStAlling cuStom AvdS Sometimes device manufacturers provide their own AVDs that you can use to emulate your applica- tions running on their devices. A good example is Samsung, which provides the Samsung Galaxy Tab add-on (http://innovator.samsungmobile.com/galaxyTab.do) for emulating their Samsung Galaxy Tab tablet. To install the Samsung Galaxy Tab add-on, fi rst launch the Android SDK and AVD Manager in Eclipse, and then select the Available Packages option on the left side of the dia- log (see Figure B-3).
- 416. 394 ❘ Appendix B Using the Android Emulator Figure B-1 Figure B-2 At the bottom of the screen, click the Add Add-on Site… button and enter the following URL: http://innovator.samsungmobile.com/android/repository/srepository.xml (see Figure B-4). Click OK.
- 417. Installing Custom AVDs ❘ 395 Figure B-3 Figure B-4 You should now see the additional package available (see Figure B-5). Check the package and click Install Selected. In the dialog that pops up, click “Accept” to accept the licensing agreement and then click Install to download and install the package. After the downloaded package is installed, you can create a new AVD based on the newly down- loaded package. Select the Virtual Devices item in the Androids SDK and AVD Manager window and click the New button. Name the new AVD as shown in Figure B-6. Click the Create AVD button to create the AVD.
- 418. 396 ❘ Appendix B Using the Android Emulator Figure B-5 Figure B-6 To launch the SamsungGalaxyTab AVD, select it and click the Start… button. The Launch Options dialog, shown in Figure B-7, will appear. Check the “Scale display to real size” option if you want to resize the emulator. This is very useful if you are running the emulator on a small monitor (such as on a notebook computer). Specify a screen size and click the Launch button to start the emulator. Figure B-8 shows the Samsung Galaxy Tab emulator.
- 419. Installing Custom AVDs ❘ 397 Figure B-7 Figure B-8
- 420. 398 ❘ Appendix B USinG the android emUlator emulAting reAl deviceS Besides using the Android Emulator to test the different configurations of Android, you can also make use of the emulator to emulate real devices, using the system images provided by device manufacturers. For example, HTC provides images for their devices running Android 1.5 and 1.6 (http://developer .htc.com/google-io-device.html#s3). You can download a device’s system image and then use the Android Emulator to emulate it using the system image. Here is how this can be done (in theory, this should work for any version of Android). NOTE If you use HTC’s image, you should be able to boot up the emulator with- out problems. However, the network cannot be enabled. Some kind souls have uploaded a modified image that works properly. You can try downloading it at www.4shared.com/get/x6pZm3-W/system.html. First, using the Android SDK and AVD Manager, create a new AVD. In the case of HTC, create an AVD using Android 1.6 as the platform. The AVD will be located in the C:Users<username> .androidavd<avd_name>.avd folder. As shown in Figure B-9, a newly created AVD contains only two fi les in the folder. Using the downloaded system image, copy the system.img fi le into the AVD folder, as shown in Figure B-10. Figure B-9 Figure B-10 Launch the AVD and you should see it booting up (see Figure B-11). You can proceed to sign in using your Google account (see Figure B-12). When prompted to slide open the keyboard, press Ctrl+F11 to change the orientation of the emulator. This action tricks the emulator into believing that you are sliding the keyboard open. Once you have successfully signed in, you will be able to explore the Android Market on your emu- lator (see Figure B-13)!
- 421. SD Card Emulation ❘ 399 Figure B-11 Do Figure B-12 SD Card Emulation When you create a new AVD, you can emulate the existence of an SD card (see Figure B-14). Simply enter the size of the SD card that you want to emulate (in the figure, it is 200MiB).
- 422. 400 ❘ Appendix B Using the Android Emulator Figure B-13 Figure B-14 Alternatively, you can simulate the presence of an SD card in the Android Emulator by creating a disk image first and then attaching it to the AVD. The mksdcard.exe utility (also located in the tools folder of the Android SDK) enables you to create an ISO disk image. The following command creates an ISO image that is 2GB in size (see also Figure B-15): mksdcard 2048M sdcard.iso
- 423. Emulating Devices with Different Screen Sizes ❘ 401 Figure B-15 Once the image is created, you can specify the location of the ISO file, as shown in Figure B-16. Figure B-16 Emulating Devices with Different Screen Sizes Besides emulating an SD card, you can also emulate devices with different screen sizes. Figure B-17 indi- cates that the AVD is emulating the WVGA854 skin, which has a resolution of 480×854 pixels. Note that the LCD density is 240, which means that this screen has a pixel density of 240 pixels per inch. Figure B-17
- 424. 402 ❘ Appendix B Using the Android Emulator For each target that you select, a list of skins is available. The Android SDK supports the following screen resolutions: ➤➤ QVGA — 240×320 ➤➤ WQVGA400 — 240×400 ➤➤ WQVGA432 — 240×432 ➤➤ HVGA — 320×480 ➤➤ WVGA800 — 480×800 ➤➤ WVGA854 — 480×854 Figure B-18 shows the Android Emulator using the WVGA854 skin. Figure B-18 Emulating Physical Capabilities In addition to emulating devices of different screen sizes, you also have the option to emulate differ- ent hardware capabilities. When creating a new AVD, clicking the New button will display a dialog for choosing the type of hardware that you want to emulate (see Figure B-19).
- 425. Sending SMS Messages to the emulator ❘ 403 For example, if you want to emulate an Android device with no touch screen, select the “Touch- screen support” property and click OK. Back in the AVD dialog, change the value of the property from yes to no (see Figure B-20). Figure B-19 Figure B-20 This will create an AVD with no touch-screen support (i.e., users won’t be able to use their mouse to click on the screen). You can also simulate location data using the Android Emulator. Chapter 9 discusses this in more details. One useful tip to make your development more productive is to keep your Android Emulator run- ning during development — avoid closing and restarting it. Because the emulator takes time to boot up, it is much better to leave it running when you are debugging your applications. Sending SmS meSSAgeS to the emulAtor You can emulate sending SMS messages to the Android Emulator using either the Dalvik Debug Monitor Service (DDMS) tool available in Eclipse, or the Telnet client. NOTE The Telnet client is not installed by default in Windows 7. To install it, type the following command line in the Windows command prompt: pkgmgr/iu:”TelnetClient”.
- 426. 404 ❘ Appendix B USinG the android emUlator keyBoArd ShortcutS The Android Emulator supports several keyboard shortcuts that enable you to mimic the behavior of a real handset. The following list shows the list of shortcuts that you can use with the emulator: ➤➤ Esc — Back ➤➤ Home — Main screen ➤➤ F2 — Toggles context-sensitive menu ➤➤ F3 — Call Log ➤➤ F4 — Lock ➤➤ F5 — Search ➤➤ F8 — Toggles data network (3G) ➤➤ Ctrl+F5 — Ringer volume up ➤➤ Ctrl+F6 — Ringer volume down ➤➤ Ctrl+F11/Ctrl+F12 — Toggle orientation For example, by pressing Ctrl+F11, you can change the orientation of the emulator to landscape mode (see Figure B-21). Figure B-21
- 427. Sending SMS Messages to the Emulator ❘ 405 Take a look at how this is done in Telnet. First, ensure that the Android Emulator is running. In order to Telnet to the emulator, you need to know the port number of the emulator. You can obtain this by looking at the title bar of the Android Emulator window. It normally starts with 5554, with each subsequent emulator having a port number incremented by two, such as 5556, 5558, and so on. Assuming that you currently have one Android Emulator running, you can Telnet to it using the fol- lowing command: C:telnet localhost 5554 To send an SMS message to the emulator, use the following command: sms send +651234567 Hello my friend! The syntax of the sms send command is as follows: sms send <phone_number> <message> Figure B-22 shows the emulator receiving the sent SMS message. Besides using Telnet for sending SMS messages, you can also use the DDMS perspective in Eclipse. If the DDMS perspective is not visible within Eclipse, you can display it by clicking the Open Perspective button (see Figure B-23) and selecting Other. Figure B-22 Figure B-23 Select the DDMS perspective (see Figure B-24) and click OK. Once the DDMS perspective is displayed, you will see the Devices tab (see Figure B-25), which shows the list of emulators currently running. Select the emulator instance to which you want to send the SMS mes- sage, and under the Emulator Control tab you will see the Telephony Actions section. In the Incoming number field, enter an arbitrary phone number and check the SMS radio button. Enter a message and click the Send button. The selected emulator will now receive the incoming SMS message. If you have multiple AVDs running at the same time, you can send SMS messages between each AVD by using the port number of the emulator as the phone number. For example, if you have an emula- tor running on port number 5554 and another on 5556, their phone numbers will be 5554 and 5556, respectively.
- 428. 406 ❘ Appendix B Using the Android Emulator Figure B-24 Figure B-25 Making Phone Calls Besides sending SMS messages to the emulator, you can also use the Telnet client to make a phone call to the emulator. To do so, simply use the following commands. To Telnet to the emulator, use this command: C:telnet localhost 5554 To make a phone call to the emulator, use this command: gsm call +651234567 The syntax of the gsm send command is as follows: gsm call <phone_number> Figure B-26 shows the emulator receiving an incoming call. Likewise, you can also use the DDMS perspective to make a phone call to the emulator. Figure B-27 shows how to make a phone call using the Telephony Actions section. As with sending SMS, you can also make phone calls between AVDs by using their port numbers as phone numbers.
- 429. Transferring Files into and out of the Emulator ❘ 407 Figure B-26 Figure B-27 Transferring Files into and out of the Emulator Occasionally, you may need to transfer files into or out of the emulator. The easiest way is to use the DDMS perspective. From the DDMS perspective, select the emulator (or device if you have a real Android device connected to your computer) and click the File Explorer tab to examine its file sys- tems (see Figure B-28).
- 430. 408 ❘ Appendix B USinG the android emUlator Figure B-28 The two buttons shown in Figure B-28 enable you to both pull a fi le from the emulator and push a fi le into the emulator. Alternatively, you can also use the adb.exe utility shipped with the Android SDK to push or pull fi les to and from the emulator. This utility, like emulator.exe, is located in the < Android_SDK_ Folder>tools folder. To copy a fi le from the connected emulator/device onto the computer, use the following command: adb.exepull/data/app/<filename>c: NOTE When using the adb.exe utility to pull or push files from or into the emula- tor, ensure that only one AVD is running. Figure B-29 shows how you can extract an APK fi le from the emulator and save it onto your computer. Figure B-29 To copy a fi le into the connected emulator/device, use the following command: adb.exepushNOTICE.txt/data/app The preceding command copies the NOTICE.txt fi le located in the current directory and saves it onto the emulator’s /data/app folder (see Figure B-30).
- 431. Resetting the Emulator ❘ 409 Figure B-30 If you need to modify the permissions of the files in the emulator, you can use the adb.exe utility together with the shell option, like this: adb.exe shell Figure B-31 shows how you can change the permissions of the NOTICE.txt file by using the chmod command. Figure B-31 Using the adb.exe utility, you can issue Unix commands against your Android Emulator. Resetting the Emulator All applications and files that you have deployed to the Android Emulator are stored in a file named userdata-qemu.img located in the C:Users<username>.androidavd<avd_name>.avd folder. For example, I have an AVD named Android_2.2_Emulator; hence, the userdata-qemu.img file is located in the C:UsersWei-Meng Lee.androidavdAndroid_2.2_Emulator.avd folder. If you want to restore the emulator to its original state (to reset it, that is), simply delete the userdata-qemu.img file.
- 433. C Answers to exercises This appendix includes the answers to the end of chapter exercises. chApter 1 AnSWerS 1 . An AVD is an Android Virtual Device. It represents an Android Emulator, which emu- lates a particular configuration of an actual Android device. 2 . The android:versionCode attribute is used to programmatically check if an application can be upgraded. It should contain a running number (an updated application should be set to a higher number than the older version). The android:versionName attribute is used mainly for displaying to the user. It is a string, such as “1.0.1”. 3 . The strings.xml file is used to store all string constants in your application. This enables you to easily localize your application by simply replacing the strings and then recompiling your application. chApter 2 AnSWerS 1 . The Android OS will display a dialog from which users can choose which activity they want to use. 2 . Intenti=new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(“http://www.amazon.com”)); startActivity(i); 3 . In an intent filter, you can specify the following: action, data, type, and category.
- 434. 412 ❘ Appendix C Answers to Exercises 4. The Toast class is used to display alerts to the user and disappears after a few seconds. The NotificationManager class is used to display notifications on the device’s status bar. The alert displayed by the NotificationManager class is persistent and can only be dismissed by the user when selected. Chapter 3 Answers 1. The dp unit is density independent and 160dp is equivalent to one inch. The px unit corresponds to an actual pixel on screen. You should always use the dp unit because it enables your activity to scale properly when run on devices of varying screen size. 2. With the advent of devices with different screen sizes, using the AbsoluteLayout makes it dif- ficult for your application to have a consistent look and feel across devices. 3. The onPause() event is fired whenever an activity is killed or sent to the background. The onSaveInstanceState() event is like the onPause() event, except that it is not always called, such as when the user presses the Back button to kill the activity. 4. The three events are onPause(), onSaveInstanceState(), and onRetainNonConfigurationInstance(). Chapter 4 Answers 1. You should check the isChecked() method of each RadioButton to determine if it has been checked. 2. You can use the getResources() method. 3. The code snippet to obtain the current date is as follows: //---get the current date--- Calendar today = Calendar.getInstance(); yr = today.get(Calendar.YEAR); month = today.get(Calendar.MONTH); day = today.get(Calendar.DAY_OF_MONTH); showDialog(DATE_DIALOG_ID); Chapter 5 Answers 1. The ImageSwitcher enables images to be displayed with animation. You can animate the image when it is being displayed, as well as when it is being replaced by another image. 2. The two methods are onCreateOptionsMenu() and onOptionsItemSelected(). 3. The two methods are onCreateContextMenu() and onContextItemSelected(). 4. To prevent launching the device’s web browser, you need to implement the WebViewClient class and override the shouldOverrideUrlLoading() method.
- 435. Chapter 9 Answers ❘ 413 Chapter 6 Answers 1. The former allows the data to be shared among all the activities in an application, whereas the latter is accessible only to the activity that created it. 2. The method name is getExternalStorageDirectory(). 3. The permission is WRITE_EXTERNAL_STORAGE. Chapter 7 Answers 1. The code is as follows: Cursor c = managedQuery( allContacts, projection, ContactsContract.Contacts.DISPLAY_NAME + “ LIKE ?”, new String[] {“%jack%”} , ContactsContract.Contacts.DISPLAY_NAME + “ ASC”); 2. The methods are getType(), onCreate(), query(), insert(), delete(), and update(). 3. The code is as follows: <provider android:name=”BooksProvider” android:authorities=”net.learn2develop.provider.Books” /> Chapter 8 Answers 1. You can either programmatically send a SMS message from within your Android application or invoke the built-in Messaging application to send it on your application’s behalf. 2. The two permissions are SEND_SMS and RECEIVE_SMS. 3. The Broadcast receiver should fire a new intent to be received by the activity. The activity should implement another BroadcastReceiver to listen for this new intent. 4. The permission is INTERNET. Chapter 9 Answers 1. The likely reasons are as follows: ➤➤ No Internet connection ➤➤ Incorrect placement of the <uses-library> element in the AndroidManifest.xml file ➤➤ Missing INTERNET permission in the AndroidManifest.xml file 2. Geocoding is the act of converting an address into its coordinates (latitude and longitude). Reverse geocoding converts a pair of location coordinates into an address.
- 436. 414 ❘ Appendix C Answers to Exercises 3. The two providers are as follows: ➤➤ LocationManager.GPS_PROVIDER ➤➤ LocationManager.NETWORK_PROVIDER 4. The method is addProximityAlert(). Chapter 10 Answers 1. This is because a service runs on the same process as the calling activity. If a service is long- running, you need to run it on a separate thread so that it does not block the activity. 2. The IntentService class is similar to the Service class, except that it runs the tasks in a separate thread and automatically stops the service when the task has finished execution. 3. The three methods are doInBackground(), onProgressUpdate(), and onPostExecute(). 4. The service can broadcast an intent, and the activity can register an intent using an IntentFilter class. Chapter 11 Answers 1. You specify the minimum Android version required using the minSdkVersion attribute in the AndroidManifest.xml file. 2. You can either use the keytool.exe utility from the Java SDK, or use Eclipse’s Export feature to generate a certificate. 3. Go to the Settings application and select the Applications item. Check the “Unknown Do sources” item.
- 437. Index Symbols ViewGroups, 82–83 Android Development Tools Views, 82–83 (ADT), 7–11 . (period), APK naming Activities, 32 Android Device Chooser, 21 convention, 16 Activity, 27–29 Android Emulator, 403–407 - (minus sign), TimePicker, 144 Context, 38 APK, 408 + (plus sign), TimePicker, 144 events, 28 AVDs, 393–397 ListActivity, 158 debugging, 36, 46, 52, 55, 69, MainActivity, 180 76, 116, 143, 144, 146, A managedQuery(), 242 148, 150, 157, 159, 162, abd.exe, 367–369, 408 MapActivity, 307 164, 174, 175, 180, 184, AbsoluteLayout, 82, 87–89, 412 methods, 114–119 189, 192, 196, 206–207, ACTION_PICK, 63 onCreate(), 82 212, 241, 266, 272, 276, actions onCreateDialog(), 34, 36 279, 287, 290, 294, 307, <intent-filter>, 70, 411 onKeyDown(), 117 309, 310, 314, 317, 324, intents, 61 setContentView(), 82 334, 337, 345, 393–409 ACTION_VIEW, 62, 70 setRequestOrientation(), devices, 398–399 activities, 22, 27–42 110–111 file transfer, 407–409 AndroidManifest.xml, 28 <activity>, 33, 110–111 localhost, 288 applications, 47 Activity.findViewById(), orientation, 106 BroadcastReceiver, 273–280 132, 134 permissions, 409 categories, 71–73 adb, 367 Phone button, 32 debugging, 31 add(), 188 phone calls, 406–407 dialog windows, 34–38 addCategory(), 72 physical capabilities, 402–403 EditText, 54, 55 addProximityAlert(), 327 resetting, 409 hiding title, 33–34 ADT. See Android Development screens, 401–402 intents, 43–78 Tools SD, 399–401 life cycle, 30–32 AlertDialog, 37 shortcut keys, 404 orientation, 104–108, 110–111 alias, 364 SMS messaging, 403–406 progress dialog, 39–42 AnalogClock, 194 testing, 18–19, 214 services anchoring Android Hierarchy Viewer, 8 binding, 350–356 orientation, 98–100 Android library, 387 communication, 346–350 RelativeLayout, 98 Android Market, 6 styles, 32–33 Android 2.3, 22 AndroidManifest.xml, 361 themes, 32–33 Android Debug Bridge, 367–369 applications, 359, 372–378 developer profile, 372–373 415
- 438. Android Packages – BroadcastReceiver Android Packages (APK), 7, 16 versions, 23, 360 Application name, 21 Android Emulator, 408 WRITE_EXTERNAL_STORAGE, 216 app_name, 24 application publishing, 359 android:minSdkVersion, 24 architecture, 3–4 deploying files, 367–378 android:orientation, 86 arguments, 61, 77 MIME, 369 android.permission.CALL_PHONE, ArrayAdapter, 143, 165 SD, 369 62 assets, 22, 199, 231 Android runtime, 4 android:screenOrientation, asynchronous calls, 296–297 110–111 asynchronous services, 338–341, android:theme, 33 343–346 11–14, 411 android:versionCode, 360, 361, AsyncTask, 296–297, 340 Android Emulator, 393–397 411 attributes AVD Manager, 21, 266 android:versionName, 360, 361 Button, 99 customization, 393–397 android.view.ViewGroup, 82 RelativeLayout, 92 testing, 21 animateTo(), 312, 315 AutoCompleteTextView, 141–144 anonymous class, 120 ArrayAdapter, 143 .ACTION_VIEW, 61 Apache License, 2 debugging, 143 , 361 API key, 303–305 EditText, 141 , 108 apiKey, 306 MainActivity.java, 142 , 70 APK. See Android Packages setThreshold(), 144 .apk, 369 simple_dropdown_item_line, 143 LAUNCHER, 24 <application>, 308, 361 Available Packages, 12 , 22 applications, 4 AVD Manager, 21, 266 , 361 activities, 47 AVDs. See Android Virtual android_layout_x, 88 anatomy, 22–25 Devices android_layout_y, 88 Android Market, 359, 372–378 android.location, 326 built-in AndroidManifest.xml, 22, 251–252 intents, 56–65 B activities, 28 SMS messaging, 269 Back button, 32, 164 <activity>, 33, 110–111 creating, 14–22 BackgroundTask, 297 Android Market, 361 databases, 231–233 Barnes and Noble, 4 <application>, 308 DDMS, 368 BaseAdapter, 176, 181 <category>, 71 digital certificates, 359, 362–366 binary data downloads, 286–288 content providers, 241 Export Android Application, debugging, 287 <intent-filter>, 65–71 363–366 MainActivity.java, 287 IntentService, 344–345 framework, 4 main.xml, 286 INTERNET, 305, 413 Gmail/Email, 281 Binder, 354 MyBrowserActivity, 70 icons, 375 bindService(), 356 networking, 284 launcher, 20 Bitmap, 287 permissions, 267, 270, 286 Manage applications, 48 BitmapFactory, 287 services, 333, 335 market, 4 BooksProvider.java, 248–251 SMS messaging, 265, 270–271 permissions, 280–281 boolean, 118 SMS_SEND, 270 publishing, 359–379 breakpoints, 389–390 <uses-sdk>, 361 versions, 360–362 BroadcastReceiver, 269, 350 web servers, 369–372 activities, 273–280 416
- 439. Browser – Dalvik Debug Monitor Service intents, 276 C ContactsContract.Contacts MainActivity, 279–280 .HAS_PHONE_NUMBER, 246 MainActivity.java, 277–278 CA. See certificate authority ContactsContract main.xml, 279 callbacks .Contacts._ID, 245 onDestroy(), 280 onCreateDialog(), 37 Content, 242 onPause(), 277, 279–280 setOnClickListener(), 134 content providers, 237–262 onResume(), 277, 279–280 showDialog(), 37 AndroidManifest.xml, 241 , 272 CallLog, 237 creating, 247–260 , 278–279 CallLog.CONTENT_URI, 243 data sharing, 237–238 cancel(), 78 debugging, 241 , 243 categories MainActivity(), 257–258 , 243 activities, 71–73 MainActivity.java, 240 , 68 Intent, 65 main.xml, 239–240, 256–257 , 37 <intent-filter>, 70, 411 queries, 238 <category>, 71–73 ContentProvider, 247 cell tower triangulation, 322 ContentResolver, 253, 255 certificate authority (CA), 362 ContentUris, 243 character array, 213 ContentValues, 223 CheckBox, 127–135 Context, 38 chmod, 409 Toast, 38 , 309–310 classes Context menu, 185, 190–193 Android library, 387 debugging, 192 , 310 anonymous, 120 MainActivity.java, 191–192 Bundle MainActivity.java, 46 CopyDB(), 232–233 getExtras(), 56, 351 Notification, 77 counter, 343 Intent, 56 Clear defaults button, 48 Create Activity, 21 key/value pairs, 56 <com.google.android.maps createFromPdu(), 272 onReceive(), 272 .MapView>, 307 CreateMenu() onSaveInstanceState, 108–109 commit(), 208 Menu, 188 putExtras(), 56 component name, 64 onCreateContextMenu(), 192 Button, 85, 113, 127–135 configuration change, orientation, Options menu, 189 android_layout_x, 88 108–109 cursor, 242 android_layout_y, 88 Confirm Perspective Switch Cursor, 244 attributes, 99 dialog, 390 moveToFirst(), 226 DatePicker, 152 connectivity, 3 queries, 223, 254 events, 117 constructors customization FrameLayout, 93–94 Intent, 61 AVDs, 393–397 id, 132 Notification, 77 ListView, 159–161 layout_width, 130 Contacts, 238, 242, 243 ProgressBar, 139–141 LinearLayout, 95–96 contacts, 221 main.xml, 98–99 ContactsContract.Contacts setOnCreateContextMenu .CONTENT_URI, 243 D Listener(), 192 ContactsContract.Contacts Dalvik Debug Monitor Service TimePicker, 146 .DISPLAY_NAME, 245 (DDMS), 8 byte stream, 213 Android Emulator, 403–407 417
- 440. Dalvik Debug Monitor Service – DoBackgroundTask Dalvik Debug Monitor DBAdapter, 218–223 perspectives, 387 Service (continued) deleteContact(), 228–229 ProgressBar, 137 applications, 368 getAllContacts(), 225–226 services, 334, 337 databases, 233 getContact(), 226–227 SMS messaging, 266, 272, internal storage, 214 onCreate(), 221–222 276, 279 Location Controls, 324 onUpgrade(), 221–222 SpinnerView, 164 perspectives, 387 SQLiteOpenHelper, 221 strings.xml, 162 screenshots, 375 updateContact(), 227–228 text file downloads, 290 SMS messaging, 272, 276, 279 DDMS. See Dalvik Debug Monitor TimePicker, 144, 146, 148 Service views, 128–129 debugging. See also Dalvik Debug Web services, 294 <intent-filter>, 70, 411 Monitor Service WebView, 196 intents, 61 activities, 31 debug.keystore, 304, 364–365 path, 238 Android Debug Bridge, 367–369 decodeStream(), persistence, 203–235 Android Device Chooser, 21 BitmapFactory, 287 databases, 218–233 Android Emulator, 36, 46, 52, 55, <Definition>, 295–296 files, 209–218 69, 76, 116, 137, 143, 144, delete(), 413 sharing, 237–238 146, 148, 150, 157, 159, 162, content providers, 252, 255 types 164, 174, 175, 180, 184, 189, deleteContact(), 228–229 ContentValues, 223 192, 196, 206–207, 212, 241, deliveryIntent, 267 getType(), 253 266, 272, 276, 279, 287, 290, Dell, 4 Intent, 64–65 294, 307, 309, 310, 314, 317, density-independent pixel. See dp <intent-filter>, 411 324, 334, 337, 345, 393–409 Desire HD, 4 data, 54 Android SDK, 303 destinationAddress, 267 /data/app, 368, 408 AutoCompleteTextView, 143 developer profile, 372–373 databases binary data downloads, 287 devices, 4–5 applications, 231–233 built-in zoom controls, 309, 310 Android Emulator, 398–399 data persistence, 218–233 certificate, 303–304 devices, 367 DDMS, 233 content providers, 241 Devices tab, 325 methods, 222–223 Context menu, 192 dialog windows pre-creating, 230–233 DatePicker, 150 activities, 34–38 Database Browser, 230 Eclipse, 389 DatePicker, 153–156 DATABASE_CREATE, 221 Gallery, 174 showDialog(), 148 databases, 224 getSharedPreferences(), TimePicker, 147–149 DATABASE_VERSION, 222, 230 206–207 Dictionary Web service, 291 DatePicker, 149–156 Google Maps, 307, 314, 317 digital certificates Button, 152 GridView, 184 applications, 359, 362–366 debugging, 150 ImageSwitcher, 180 keytool.exe, 362 dialog windows, 153–156 ImageView, 175 DigitalClock, 194 MainActivity.java, 150–151, IntentService, 345 Display, 110 153–155 internal storage, 212 Display Notification button, 76 onDateSet(), 156 ListView, 157, 159 DisplayContact(), 226 DatePickerDialog, 156 Location Manager, 324 DistributionKeyStoreAlias, 364 day, 156 Options menu, 189 DoBackgroundTask, 341 418
- 441. Document – getService() Document, 294–295 onFocusChange(), 120–121 Flash support, 3 DocumentBuilder, 294 orientation, 106, 108 flush(), 213 DocumentBuilderFactory, 294 SeekBar, 207 FrameLayout, 82, 93–95 doInBackground(), 297, 340, 414 setHint(), 56 fromPixels(), 319 doSomethingRepeatedly(), 343 e-mail, 281–283 doSomeWork() Intent, 283 progressStatus, 141 MainActivity.java, 282–283 G , 138 main.xml, 282 Galaxy Tab, 4 , 369 putExtra(), 283 Gallery, 170–176 setData(), 283 debugging, 174 setType(), 283 MainActivity.java, 172–174 Emulator Control tab, 325 main.xml, 171, 176 emulator.exe, 408 gen, 22 , 337 e-reader devices, 4–5 Geocoder, 320–321 , 287 events geocoding, 320–322, 413 , 291 Activity, 28 GeoPoint, 314, 318, 319 Button, 117 GET, 291 , 23 EditText, 117 get(), 351 , 22E handlers, 120 getAction(), 319 views, 119–121, 133–135 getActivity(), 77 exceptions, 390–392 getAllContacts(), 225–226 execute(), 341, 351 getBaseContext(), 38 onStartCommand(), 355 getContact(), 226–227 Android Device Chooser, 21 Export Android Application, getCurrentHour(), 146–147 breakpoints, 389–390 363–366 getCurrentMinute(), 146 code completion, 388 Export dialog, 363 getData(), 54 debugging, 389 external storage, 214–216 getDayOfMonth(), 153 editors, 385–386 getDefault(), 267 exceptions, 390–392 getDefaultDisplay(), 110 F IDE for Java EE Developers, 6–7 getExternalStorageDirectory(), Package Explorer, 382–383 features, 3 215, 413 perspectives, 387 files getExtras(), 56, 351 refactoring, 388–389 data persistence, 209–218 getFromLocation(), 320–321 R.java, 24 transfer, 407–409 getFromLocationName(), 321 workspaces, 381–382 File Explorer tab, 407 getIntent(), 56 eclipse.exe, 7 FILE_DOWNLOAD_ACTION, 349 getListView(), 160 Editor, 207 FileInputStream, 213 getMonth(), 153 editors, Eclipse, 385–386 FileOutputStream, 213 getOriginatingAddress(), EditText, 127–135 fill_parent, 84, 130 272–273 activities, 54, 55 filtering. See also <intent-filter> getPackageInfo(), 360–361 AutoCompleteTextView, 141 IntentFilter, 349, 414 getPreferences(), 208–209 events, 117 ListView, 160 getProjection(), 319 internal storage, 212 setTextFilterEnabled(), 160 getResources(), 162, 412 LinearLayout, 95–96 finish(), 53 getService(), 354, 356 419
- 442. getSharedPreferences() – IntentService getSharedPreferences(), 204–208 http://, 70 integrated development debugging, 206–207 HTTP_OK, 286 environment (IDE), 6 MainActivity.java, 205–206 HttpURLConnection, 286 Intent, 64–65 main.xml, 204–205 addCategory(), 72 getString(), 56 arguments, 61 getSystemService(), 326 I bindService(), 356 getType(), 413 icon.png, 23, 385 Bundle, 56 content providers, 253 icons categories, 65 data types, 253 android:icon, 361 constructors, 61 MIME, 252 applications, 375 data types, 64–65 , 153 id, 238 e-mail, 283 Button, 132 key/value pairs, 77 , 138 IDE. See integrated development MainActivity.java, 355 environment NotificationView, 76 Android SDK, 303 IIS. See Internet Information Object, 351 API key, 303–305 Server onStartCommand(), 351 built-in zoom controls, 308–310 ImageAdapter passing data, 54–56 debugging, 307, 314, 317 BaseAdapter, 176, 181 request code, 53 displaying, 305–308 GridView, 184–185 setData(), 53, 64 geocoding, 320–322 ImageView, 181 SMS messaging, 272, 276 INTERNET, 307 ImageButton, 127–135 startActivityForResult(), 63 MainActivity.java, 306–307, ImageSwitcher, 177–181, 412 URL, 350–351 313–317 debugging, 180 intents main.xml, 306 MainActivity.java, 178–180 actions, 61 markers, 315–318 main.xml, 177 activities, 43–78 navigation, 312–315 makeView(), 180 BroadcastReceiver, 276 reverse geocoding, 318, 320–322 onCreate(), 181 built-in applications, 56–65 views, 310–312 View, 181 data, 61 Google TV, 4 ViewFactory, 180 notifications, 73–78 GridView, 181–185 ImageView, 170–176 resolution, 48–49, 64 groupId, 188 AsyncTask, 296 results, 50–54 debugging, 175 SMS messaging, 269–270 FrameLayout, 93 TextView, 277 H IntentFilter, 349, 414 GridView, 181 hardware support, 3 ImageAdapter, 181 <intent-filter>, 24, 411 helper methods, 186–188 MainActivity.java, 175 actions, 70 hint text, 55 main.xml, 171, 176 AndroidManifest.xml, 65–71 Home button, 19, 32 import, namespaces, 387 categories, 70 horizontal, 132 InputStream, 233, 286 data, 70 HTC, 4, 398 InputStreamReader, 213, 291 intent resolution, 48–49 HTML, 198–199 insert(), 252, 254–255, 413 services, 335 HTTP, 284–286 insertContact(), 224 Intent.FLAG_ACTIVITY GET, 291 Install button, 281, 370 _NEW_TASK, 280 WordDefinition(), 294 IntentService, 343–346, 414 420
- 443. internal storage – MainActivity internal storage landscape orientation, 97, list views, 156–165 DDMS, 214 102–103, 104 ListActivity, 158, 160 debugging, 212 Launch my Browser button, 69 listener, 326 EditText, 212 Launch Options dialog, 396 ListView, 156–162, 242 MainActivity.java, 210–212 layout, 101–102 customization, 159–161 main.xml, 209 Layout view, 17 debugging, 157, 159 save, 209–214 layout_alignLeft, 92 filtering, 160 layout_alignParentBottom, 99 getListView(), 160 , 305, 413 layout_alignParentLeft, 92, 99 ListActivity, 158 layout_alignParentRight, 99 MainActivity.java, 157, 159 layout_alignParentTop, 92, 99 main.xml, 158 layout_alignRight, 92 onListItemClick(), 158 Server (IIS), 369 layout_below, 92 ScrollView, 95 layout_centerHorizontal, 92, 99 setChoiceMode(), 160 , 315 layout_centerVertical, 99 simple_list_item_1, 158 , 138 layout_gravity, 84, 85–86 Load button, 215–216 , 135, 412 layout_height, 83, 131 loadDataWithBaseURL(), 198–199 , 307 layout-land, 102–103 loadUrl(), 196, 199 , 188 layout_marginBottom, 83 localhost, 288 layout_marginLeft, 83 Location Controls, 324 layout_marginRight, 83 Location Manager, 281, 322–327 layout_marginTop, 83 debugging, 324 LayoutParams, 112, 113 MainActivity.java, 322–324 .java, 22, 385 layout_weight, 84, 85–86 location-based services (LBS), Java EE, 6–7, 387 layout_width, 83 301–329 Java SE Development Kit (JDK), 7 Button, 130 Google Maps, 13, 302–322 java.io, 209 fill_parent, 130 location data, 322–327 JDK. See Java SE Development Kit RadioButton, 132 LocationListener, 326 wrap_content, 84, 130, 132 LocationManager, 326, 327 layout_x, 84 LocationManager K layout_y, 84 .GPS_PROVIDER, 414 KeyEvent.KEYCODE_DPAD_CENTER, 47 LBS. See location-based services LocationManager.NETWORK_ keystores, 304, 363–364 LG, 4 PROVIDER, 414 keytool.exe, 304–305 libraries, 4, 305, 387, 413 LogCat, 31, 32, 230 digital certificates, 362 LinearLayout, 82, 83–87, 112–114 orientation, 106 key/value pairs Button, 95–96 PrintContacts(), 245 Bundle, 56 EditText, 95–96 services, 339, 342 ContentValues, 223 layout_gravity, 85–86 Start Service button, 345 Intent, 77 LayoutParams, 113 keywords, 281 layout_weight, 85–86 main.xml, 83 M ScrollView, 95–96 MainActivity, 22 L <LinearLayout>, 83, 130 Activity, 180 label view. See TextView Linux kernel, 4 BroadcastReceiver, 279–280 421
- 444. MainActivity – messaging MainActivity (continued) main.xml, 17, 18, 22, 23, 46, Manage applications, 48 ListActivity, 158 66–67, 87–88 managed cursor, 242 onKeyDown(), 117 AutoCompleteTextView, 141–142 managedQuery() String, 143 binary data downloads, 286 Activity, 242 MainActivity(), 257–258 BroadcastReceiver, 279 ORDER BY, 247 MainActivity.java, 22, 30, 35, 45, Button, 98–99 projections, 246 67–68 content providers, 239–240, WHERE, 246 AutoCompleteTextView, 142 256–257 <manifest>, 361 binary data downloads, 287 copy, 44 Manual tab, 325 BroadcastReceiver, 277–278 e-mail, 282 MapActivity, 307 built-in zoom controls, 309–310 FrameLayout, 93 MapController, 310 class, 46 Gallery, 171, 176 animateTo(), 312, 315 content providers, 240 getSharedPreferences(), MapView, 314 Context menu, 191–192 204–205 MapOverlay, 318, 319 DatePicker, 150–151, 153–155 Google Maps, 306 maps.jar, 303 e-mail, 282–283 GridView, 182 MapView, 310 Gallery, 172–174 ImageSwitcher, 177 invalidate(), 315 getSharedPreferences(), ImageView, 171, 176 MapController, 314 205–206 internal storage, 209 MapOverlay, 318 Google Maps, 306–307, layout, 101–102 onTouchEvent(), 319 313–317 layout-land, 102–103 setSatellite(), 310–311 GridView, 182–184 LinearLayout, 83 UI, 305 ImageSwitcher, 178–180 ListView, 158 markers, 315–318 Intent, 355 ProgressBar, 136, 139 MD5 IntentService, 345 <ProgressBar>, 138 debug.keystore, 364–365 internal storage, 210–212 RelativeLayout, 91–92 Keytool.exe, 304–305 ListView, 157, 159 res/layout, 81–82, 126, measurement units, 85 Location Manager, 322–324 127–128, 136, 141–142, media support, 3 LocationManager, 326 144, 163, 386 MediaStore, 238 networking, 284–285 R.layout.main, 25 MediaStore.Images.Media onKeyDown, 47 ScrollView, 95–96 .EXTERNAL_CONTENT_URI, 243 OpenHttpConnection(), 285 services, 333 MediaStore.Images.Media Options menu, 188–189 setContentView(), 25 .INTERNAL_CONTENT_URI, 243 orientation, 105–106 SMS messaging, 265, 273 Menu ProgressBar, 136–137, 139–140 SpinnerView, 163 CreateMenu(), 188 services, 333–334, 336–337 startActivityForResult(), 50 setQuertyMode(), 193 SMS messaging, 265–266, 274–275 TableLayout, 89–90 menus SpinnerView, 163–164 <TextView>, 126 helper methods, 186–188 startActivityForResult(), 51 TimePicker, 144 views, 185–193 strings.xml, 162 UI, 112 MENU button, 189, 190 text file downloads, 289–290 WebView, 195 MenuChoice(), 188, 189, 193 TimePicker, 145–148 Make Calls button, 59 MenuItem, 188 Web services, 292–294 makeView(), 180 messaging. See SMS messaging WebView, 195–196 422
- 445. methods – onStartCommand() methods NOOKcolor, 4 onDateSet(), 156 Activity, 114–119 NOTICE.txt, 409 onDestroy(), 28, 32 add(), 188 NotifcationManager, 73–78 BroadcastReceiver, 280 databases, 222–223 Notification, 77 stopService(), 335 MIME, 369 notifications onFocusChange(), 120–121 getType(), 252 intents, 73–78 onHandleIntent(), 346 setType(), 64–65 UI, 114–121 onKeyDown(), 114 notification bar. See status bar Activity, 117 NotificationManager, 77, 412 boolean, 118 , 326 NotificationView, 76, 78 built-in zoom controls, 310 , 414 NotificationView.java, 73 MainActivity, 117 , 326 notification.xml, 73 MainActivity.java, 47 , 400 notify(), 78 onKeyUp, 114 notifyChange(), 255 onListItemClick(), 158 , 207, 213 onLocationChanged(), 326 , 213 onMenuItemSelected, 114 , 156 O onMenuOpened, 114 , 319 Object, 351 onNothingSelected(), 164 , 226 onBind(), 335, 354 onOptionsItemSelected(), 189, 412 onCheckedChanged(), 135 onPause(), 28, 412 onClick() BroadcastReceiver, 277, 279–280 Load button, 215–216 orientation, 106, 108 Save button, 214 onPostExecute(), 297, 340, 414 MyBrowserActivity, 70, 72 SD, 214 onProgressUpdate(), 340, 414 MyBrowserActivity.java, 65, 68–69 Start Service button, 356 onProviderDisabled(), 326 MyDB, 221, 224 views, 135 onProviderEnabled(), 326 MyLocationListener, 326 onContextItemSelected(), 193 onReceive(), 269 onCreate(), 25, 28, 413 Bundle, 272 Activity, 82 SMSReceiver, 280 N onRestart(), 28, 32 content providers, 252, 254 Name, 56 DBAdapter, 221–222 onRestoreInstanceState(), 108 namespaces, 387 ImageSwitcher, 181 onResume(), 28, 32 navigation, 312–315 onRestoreInstanceState(), 108 BroadcastReceiver, 277, 279–280 netbooks, 4–5 orientation, 97, 111 onRetainNonConfiguration net.learn2develop.MyBrowser, 70 setContentView(), 158 Instance(), 109, 412 networking, 284–297 setListAdapter(), 158 onSaveInstanceState(), 412 AndroidManifest.xml, 284 UI, 29, 82 Bundle, 108–109 asynchronous calls, 296–297 views, 134 orientation, 108 binary data downloads, 286–288 onCreateContextMenu(), 192 onServiceConnected(), 356 HTTP, 284–286 onCreateDialog(), 34, 36 onServiceDisconnected(), 356 MainActivity.java, 284–285 callbacks, 37 onStart(), 28, 32 text file downloads, 288–291 showDialog(), 148 onStartCommand(), 335 Web services, 291–296 onCreateOptionsMenu(), 189, 412 execute(), 355 Intent, 351 423
- 446. onStatusChanged() – RadioButton onStatusChanged(), 326 P style, 141 onStop(), 28 Visibility, 138 onTimeSet(), 149 Package Explorer, 16, 382–383 <ProgressBar>, 138 onTouchEvent(), 319 Package name, 21 ProgressDialog, 41 onUpgrade(), 221–222 PackageManager, 360–361 progressStatus, 141 Open button, 370 parse(), 61 Project name, 21 openFileOutput(), 213 Paste, 44 projections, 246 PDU, 272 provider, 326 DownloadImage(), 287 PendingIntent, 267, 269 pt, 85 InputStream, 286 getActivity(), 77 publishing applications, 359–379 MainActivity.java, 285 People of Lava, 4 Push a file onto the device permissions button, 368 Android Emulator, 409 put(), 223 CreateMenu(), 189 AndroidManifest.xml, 267, putBoolean(), 207 debugging, 189 270, 286 putExtra(), 269, 350 MainActivity.java, 188–189 android.permission e-mail, 283 , 188 .CALL_PHONE, 62 PutExtras(), 56 , 247 applications, 280–281 putFloat(), 208 Install button, 281 putInt(), 208 activities, 104–108, 110–111 INTERNET, 286, 413 putLong(), 207 anchoring, 98–100 persisting state, 108–109 putString(), 207 Android Emulator, 106 perspectives, 387 px, 85, 401 configuration change, 108–109 Phone application, 59 EditText, 106, 108 Phone button, 32 landscape, 97, 102–103, 104 phone calls, 406–407 Q LogCat, 106 physical capabilities, 402–403 queries. See also managedQuery() MainActivity.java, 105–106 picker views, 144–156 Contacts, 243 managing changes, 104–108 pictures, 169–185 content providers, 238 onCreate(), 97, 111 pixel. See px Cursor, 223, 254 onPause(), 106, 108 placeholder text, 55 strings, 238 onSaveInstanceState(), 108 point. See pt predefined constants, 243–246 persisting state, 108–109 portrait, 111 title, 254 portrait, 97, 103 portrait orientation, 97, 103 query(), 413 resizing and repositioning, predefined constants, 243–246 content providers, 252, 254 101–104 PrintContacts(), 245 res/layout, 101 private keys, 364 UI, 97–111 progress dialog, 39–42 R WindowManager, 109 ProgressBar, 135–141 RadioButton, 127–135 XML, 104 customization, 139–141 horizontal, 132 orientation, 132 debugging, 137 isChecked(), 135 OutputStream, 233 MainActivity.java, 136–137, layout_width, 132 Overlay, 317–318 139–140 onCheckedChanged(), 135 setMax, 141 orientation, 132 424
- 447. RadioGroup – setPositiveButton() RadioGroup, 131 Runnable, 138 service, 356 setOnCheckedChange runtime, 4 services, 331–356 Listener(), 135 activities RadioGroup, 127–135 binding, 350–356 RadioButton, 131 S communication, 346–350 setOnCheckedChange -s, 367 AndroidManifest.xml, 333, 335 Listener(), 135 Samsung, 4 asynchronous, 338–341 , 213 satellite view, 310–311 IntentService, 343–346 , 413 save debugging, 334, 337 external storage, 214–216 <intent-filter>, 335 , 349 internal storage, 209–214 LogCat, 339, 342 , 82, 91–92 onSaveInstanceState(), long-running tasks, 336–341 108–109, 412 MainActivity.java, 333–334, user preferences, 203–209 336–337 , 93 Save button, 214 main.xml, 333 , 98–99 scAddress, 267 repeated tasks, 341–343 scale-independent pixel. See sp serviceBinder, 355, 356 Scandinavia Android TV, 4 ServiceConnection, 355 , 326 scheduleAtFixedRate(), 343 bindService(), 356 , 33 screens. See also orientation setAlphabeticShortcut(), 188 , 22 Android Emulator, 401–402 setBuiltInZoomControls(), screenshots, 375 196, 309 , 25, 44 ScrollView, 82, 95–97 setChoiceMode(), 160 main.xml, 81–82, 126, 127–128, FrameLayout, 95 setContentView() 136, 141–142, 144, 163, 386 LinearLayout, 95–96 Activity, 82 notification.xml, 73 ListView, 95 main.xml, 25 orientation, 101 main.xml, 95–96 onCreate(), 158 UI, 28 SD. See secure digital UI, 112 Resolver getContentResolver(), 242 secure digital (SD), 12, 214–216 setData(), 62 Do res/raw, 217–218 Android Emulator, 399–401 e-mail, 283 results, 50–54 APK, 369 Intent, 53, 64 RESULT_CANCELLED, 53 onClick(), 214 SetHint(), 56 RESULT_OK, 53 SeekBar, 207 setIs24HourView(), 146 res/values, 23 self-signed certificates, 359, 362 setLatestEventInfo(), 78 strings.xml, 161, 163 Send button, 325 setListAdapter(), 158 reverse geocoding, 318, 320–322 Send Email button, 283 setMax, 141 RIM. See Research In Motion sendBroadcast(), 348–349 setMultiChoiceItems(), 38 R.java, 18, 22, 24 BroadcastReceiver, 272 setNegativeButton(), 38 R.layout.main, 25 SEND_SMS, 413 setOnCheckedChangeListener(), 135 RSS Reader, 288 sendTextMessage(), 267 setOnClickListener(), 134 run(), 343 sensor, 111 setOnCreateContextMenu doSomeWork(), 138 sentIntent, 267 Listener(), 191, 192 Service, 335, 344, 414 setPositiveButton(), 38 425
- 448. setProgress() – Telnet setProgress(), 141 intents, 269–270 startActivityForResult(), setQuertyMode(), 193 TextView, 277 50–54, 70 setRequestOrientation(), 110–111 keywords, 281 Intent, 63 setResult(), 53 MainActivity.java, 265–266, MainActivity.java, 51 setSatellite(), 310–311 274–275 main.xml, 50 setStreetView(), 311–312 main.xml, 265, 273 startService(), 335, 343 setTextFilterEnabled(), 160 MIME, 269 START_STICKY, 335 , 144 receiving, 270–280 static resources, 217–218 sending programmatically, status bar, 73–78 Manage applications, 48 264–267 Display Notification button, 76 , 243 TextView, 273, 276, 277 NotificationView, 76 , 311–312 Toast, 272 ticket text, 77 SMS_DELIVERED, 269 Stop Service button, 334 e-mail, 283 SmsManager, 267 stopSelf(), 341, 343 MIME, 64–65 SMSReceiver, 280 stopService(), 341, 343 , 315 SMSReceiver.java, 273–274 onDestroy(), 335 BroadcastReceiver, 278–279 storage, 3 XML, 208 src, 271 external, 214–216 , 203–209 SMS_SEND, 270 internal, 209–214 SMS_SENT, 269 Streak, 4 Android Emulator, 404 Sony, 4 street view, 311–312 setAlphabeticShortcut(), 188 sp, 85 String, 213 setQueryMode(), 193 SpinnerView, 162–165 InputStreamReader, 291 shouldOverrideUrlLoading(), 412 debugging, 164 MainActivity, 143 Show Map button, 59 MainActivity.java, 163–164 @string, 23 showDialog(), 37 main.xml, 163 strings.xml, 23, 161–162, 411 callbacks, 37 strings.xml, 163 app_name, 24 dialog windows, 148 SQLite, 3, 218 debugging, 162 onCreateDialog(), 148 Database Browser, 230 getResources(), 162 SimpleCursorAdapter, 242 SQLiteOpenHelper, 253 MainActivity.java, 162 simple_dropdown_item_line, 143 DBAdapter, 221 res/values, 163 simple_list_item_1, 158 src, 22 SpinnerView, 163 smartphones, 4–5 ImageButton, 131 style, 141 SMS messaging, 3, 263–281, 413 NotificationView.java, 73 styles, 32–33 Android Emulator, 403–406 SMSReceiver.java, 271 Switch Workspace, 383–385 AndroidManifest.xml, 265, standard prefix, 238 270–271 Start Service button, 342 AVD Manager, 266 LogCat, 345 T built-in applications, 269 onClick(), 356 TableLayout, 82, 89–91 DDMS, 272, 276, 279 Toast, 337, 339, 348 <TableRow>, 89 debugging, 266, 272, 276, 279 startActivity(), 47, 48, 70 tablets, 4–5 feedback, 267–269 Intent.FLAG_ACTIVITY_NEW_ Telephony Actions, 406 Intent, 272, 276 TASK, 280 Telnet, 403, 405 426
- 449. testing – WindowManager testing. See also debugging DATABASE_VERSION, 222, 230 U Android Emulator, 18–19, 214 Min SDK Version, 21 AVDs, 21 UI. See user interface minSdkVersion, 414 tethering, 3 update(), 413 View, 181 text, 267 content providers, 252, 255–256 views. See also specific views text file downloads, 288–291 updateContact(), 227–228 activities, 82–83 debugging, 290 URI, 238 debugging, 128–129 , 289–290 Uri, 61 events, 119–121, 133–135 , 217–218 UriMatcher, 253 Google Maps, 310–312 , 85, 113, 126 URL list, 156–165 , 38 Intent, 350–351 menus, 185–193 , 242 Object, 351 onClick(), 135 urls, 355 onCreate(), 134 intents, 277 user interface (UI), 81–123 picker, 144–156 , 90 AbsoluteLayout, 88 pictures, 169–185 , 83 creating programmatically, UI, 125–168 , 84 111–114 ViewFactory, 180 , 126 main.xml, 17, 22, 23, 46, View.findViewById(), 132 , 90 87–88, 112 ViewGroups, 82–83 MapView, 305 Visibility, 138 , 138 notifications, 114–121 vnd.android-dir/mms-sms, 269 , 337 onCreate(), 29, 82 orientation, 97–111 TimePicker, 144–149 res/layout, 28 W Button, 146 setContentView(), 112 Web Browser button, 59 debugging, 144, 146, 148 TimePicker, 146 web servers, 369–372 dialog windows, 147–149 views, 125–168 Web services MainActivity.java, 145–148 XML, 82, 386 debugging, 294 onTimeSet(), 149 user preferences, 203–209 MainActivity.java, 292–294 UI, 146 user-data-qemu.img, 409 networking, 291–296 TimePickerDialog, 149 <uses-library>, 305, 413 WebSettings, 196 Timer, 343 <uses-sdk>, 24, 361 WebView, 194–200 TimerTask, 343 debugging, 196 title, 188 HTML, 198–199 V queries, 254 loadUrl(), 196, 199 Toast, 36, 174, 188, 412 values, 22 MainActivity.java, 195–196 Context, 38 versions, 2 main.xml, 195 Geocoder, 321 AndroidManifest.xml, 23, 360 WebViewClient, 412 SMS messaging, 272 android:minSdkVersion, 24 WHERE, 246 Start Service button, 337, 339, android:versionCode, 360, while, 141 348 361, 411 Wi-Fi triangulation, 322 ToggleButton, 127–135 android:versionName, 360, 361 Window.FEATURE_NO_TITLE, 33 tools, 400 applications, 360–362 WindowManager, 109 427
- 450. withAppendedId() – zoomOut() withAppendedId(), 243 WRITE_EXTERNAL_STORAGE, 413 Y WordDefinition(), 294 AndroidManifest.xml, 216 <WordDefinition>, 295–296 yr, 156 workspaces Eclipse, 381–382 X Z Switch Workspace, 383–385 XML wrap_content downloads, 291 zoom. See built-in zoom controls layout_height, 131 orientation, 104 zoomIn(), 309, 310 layout_width, 84, 130, 132 shared preferences, 208 zoomOut(), 309, 310 , 213 UI, 82, 386 428