Android casting-wide-net-android-devices

Casting a Wide Net:
Targeting All Android Devices
Justin Mattson
Developer Advocate
19 May 2010

Tuesday, May 25, 2010

House keeping
Use Wave to see live notes and ask questions

http://tinyurl.com/io10casting

3


Agenda
Resource Loading
Image & Drawable Considerations
Adapting to API Availability
Testing

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Resource Loading
• Based on current system configuration
• If config changes, your app restarts (eg. orientation change)
• Hierarchy of qualifiers

5


Resource loading
Screen size
• Physical size of the screen
• Buckets
– small: <~3.0”
– normal: ~3.0” - ~4.0”
– large: >~4.0”

6


Resource loading
Screen orientation
• landscape, portrait, or
square
• Might be triggered by
accelerometers or other
events

7


Resource loading
Screen density
• Pixels per unit of measurement
• System looks for “best” fit*
• Buckets
– ldpi: ~120dpi
– mdpi: ~160dpi
– hdpi: ~240dpi
• *Matching: everyone is a
winner
– first match on 1.5

8


Resource loading
SDK Version
• Styles across versions

• Inexact matching, <= current
version

• Work around 1.5 dpi bug
– Exact matching on 1.5 - 2.0
– v5 thinks its v6

9


Image resources


Image Resources
• Goal is uniform physical sizing across screens
• Best match allows for up or down sampling based on
available resources
– Single or few pixel features are most obviously impacted

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Image Resources
The trouble with pixels

12


Manipulating Image Loading
• DO NOT DO THIS
• OKAY, okay, if you must...
• Only possible (and sensical) on 1.6 and above
• Bitmap scaling controlled by density attributes of the object
• Normally...
BitmapFactory.Options default = new BitmapFactory.Options();
default.inDensity = <density of loaded resource>
default.inTargetDensity =
getResources().getDisplayMetrics().densityDpi;

• Pixels are scaled by inTargetDensity/inDensity
• Manually set inDensity = inTargetDensity =
DisplayMetrics.densityDpi

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Nine-Patches
• Use to create image resources that can stretch controllably
• One set of controls for stretching, another for the content
area

14


Nine-Patches
Stretching to fill the space

15


Nine-Patches
A little cushion

16


Drawables


Shapes
• Draw optimized views, regardless of screen
• Primitives like square, oval, rectangle
• Use these as the basis for simple graphics instead of
bitmaps
• Shape.draw() makes it easy to build a custom view

18


Shapes
public class LogoView extends View {
private Shape mShape = new RectShape();
private Drawable mLogo;
public LogoView (Context context) {
super(context);
mLogo = getContext().getResources()
.getDrawable(R.id.logo);
}
protected void onDraw(Canvas canvas) {
mShape.resize(canvas.getWidth(), canvas.getHeight());
mShape.draw(canvas, mLogoBackgroundPaint);
mLogo.draw(canvas);
}
}
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ScaleDrawable
• Adapt your drawables in a custom manner based on screen
• Wraps another drawable
• Allows for more exact control over scaling
• Ideal for situations where it doesn’t make sense to preserve
aspect ratio
– Progress bars
– Dividers
– Any place where one dimension is more important than the
other

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LevelListDrawable
• Specified in XML
• Combines a group of resources into a drawable
• Use where the drawable is logically the same, but
presentation varies based on state
– status meters (eg. battery, signal)
– weather condition
– sports team
– UI theme
• For cases without a natural “level”, define constants making
code more readable
• Select the right resource for the right UI theme

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LevelListDrawable
<?xml version="1.0" encoding="utf-8"?>
<level-list xmlns:android="http://schemas.android.com/apk/
res/android">
<item android:maxLevel="0"
android:drawable="@drawable/rain_chance_zero"/>
android:drawable="@drawable/rain_chance_slight"/>
android:drawable="@drawable/rain_chance_good"/>
android:drawable="@drawable/rain_chance_high"/>
</level-list>

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LevelListDrawable

public class IO_Demo extends Activity {
public void onResume() {
((ImageView)findViewBy(R.id.weather))
.setImageLevel(getRainChance());
}

private int getRainChance() {
// call web service to get forecast
}
}

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LevelListDrawable

Thanks to openclipart.org from for the Public Domain clipart used on this slide.
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Cross-Version Compatibility


API Changes: New Classes
• Runtime handling of class load failures
• Class dependencies resolved when class is first loaded
• Use a second class with a static method to provoke class
verification
• Catch any verification error and adapt behavior
• Avoids messy Class.forName(“”) pattern, but grows number
of classes needed
– group in a single package or as inner classes

26


public class Canary {
private static NEW_CLASS foo;

public static void tryNewClass() {
foo = new NEW_CLASS();
}
}

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public class MyActivity extends Activity {
private boolean canaryAvailable;
private void checkApis() {
try {
Canary.tryNewClass();
canaryAvailable = true;
} catch (VerifyError e) {
canaryAvailable = false;
Log.w(LOG_TAG, “Canary unavailable, falling back.”);
}
}

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API Changes: New Methods
• A bit trickier than dealing with classes
• Determining which APIs are available
– Use reflection to check availability
– Make your code version aware
• Working with availability
– Call through using reflection (fewer classes)
– Write a factory to return the right class (cleaner)

29


API Changes: Mirror, mirror...
private static Method getDensity;
static {
getDensity = Canvas.class.getMethod(“getDensity”, null);
} catch (NoSuchMethodException e) {
Log.w(LOG_TAG, “getDensity method not available.”);
}
}

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API Changes: Mirror, mirror...
private static boolean hasDensity;
private Canvas mDrawingSurface;
public Integer getDensity() {
if (getDensity != null) {
return (Integer) getDensity.invoke(mDrawingSurface,
null);
} else {
return DEFAULT;
}
}

31


Testing


Testing, testing, testing
• Nothing beats it
• Verify the UI is behaving as expected
• Check that any API compatibility code functions properly
• Hardware testing is hopefully unnecessary, but...

33


Questions?
Use Wave to see live notes and ask questions

http://tinyurl.com/io10casting

34


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