Android Data Binding in action using MVVM pattern - droidconUK

#droidconUK
Android Data Binding in action
using MVVM pattern
Fabio Collini
droidcon London
October 2016

2
Ego slide
@fabioCollini
linkedin.com/in/fabiocollini
github.com/fabioCollini
medium.com/@fabioCollini
codingjam.it

3
Agenda
1. Data Binding basics
2. Custom attributes
3. Components
4. Two Way Data Binding
5. Data Binding + RxJava
6. Model View ViewModel

#droidconUK - London - October 2016 - @fabioCollini 4
1Data Binding basics

Google I/O 2016
5
Google I/O 2015

6
github.com/fabioCollini/DataBindingInAction

7
match_result.xml
<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout style="@style/root_layout" 
xmlns:android=“http://schemas.android.com/apk/res/android">
 
<ImageView android:id="@+id/result_gif" style="@style/gif"/> 
 
<LinearLayout style="@style/team_layout"> 
<TextView android:id="@+id/home_team" style="@style/name"/> 
<TextView android:id="@+id/home_goals" style="@style/goals"/> 
</LinearLayout> 
 
<TextView android:id="@+id/away_team" style="@style/name"/> 
<TextView android:id="@+id/away_goals" style="@style/goals"/> 
</LinearLayout> 
</LinearLayout>

8
public class TeamScore { 
private final String name; 
private final int goals;
//constructor and getters 
}
public class MatchResult { 
private final TeamScore homeTeam; 
private final TeamScore awayTeam; 
private final String gifUrl;
//constructor and getters 
}

dataBinding { 
enabled = true 
} 
9
build.gradle
android { 
//... 
//... 
 
defaultConfig { 
//... 
____} 
buildTypes { 
//... 
____}
}

<layout> 
<LinearLayout style=“@style/root_layout"
xmlns:android="http://schemas.android.com/apk/res/android"> 
 
 
</LinearLayout> 
 
</LinearLayout> 
</LinearLayout> 
</layout>
10
Data Binding layout
 
 
</LinearLayout> 
 
</LinearLayout> 
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<layout>
</layout>

 
 
</LinearLayout> 
 
</LinearLayout> 
</LinearLayout>
11
One layout traversal
match_result.xmlMatchResultBinding.java
Auto generated class
<?xml version="1.0" encoding="utf-8"?>
<layout>
</layout>
public class MatchResultBinding extends
android.databinding.ViewDataBinding { 
 
// ... 
public final android.widget.ImageView resultGif; 
public final android.widget.TextView homeTeam; 
public final android.widget.TextView homeGoals; 
public final android.widget.TextView awayTeam; 
public final android.widget.TextView awayGoals; 
// ... 
}

12
public class MatchResultActivity extends AppCompatActivity { 
 
private MatchResultBinding binding; 
 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
 
binding = DataBindingUtil.setContentView(this, R.layout.match_result); 
 
MatchResult result = getIntent().getParcelableExtra("RESULT"); 
 
if (result.getHomeTeam() != null) { 
binding.homeTeam.setText(result.getHomeTeam().getName()); 
binding.homeGoals.setText(
Integer.toString(result.getHomeTeam().getGoals())); 
}if1 
if (result.getAwayTeam() != null) { 
binding.awayTeam.setText(result.getAwayTeam().getName()); 
binding.awayGoals.setText(
Integer.toString(result.getAwayTeam().getGoals())); 
}if 
Glide.with(this).load(result.getGifUrl()) 
.placeholder(R.drawable.loading).into(binding.resultGif); 
}onCreate 
}activity

13
Variable in layout
<layout xmlns:android="http://schemas.android.com/apk/res/android">
Automatic null check
<data> 
<variable name="result"
type="it.droidcon.databinding.MatchResult"/> 
</data>
<LinearLayout style="@style/root_layout"> 
 
<TextView style=“@style/name" 
android:text="@{result.homeTeam.name}"/> 
<TextView style="@style/goals" 
android:text="@{Integer.toString(result.homeTeam.goals)}"/> 
</LinearLayout> 
 
<TextView style="@style/name" 
android:text="@{result.awayTeam.name}"/> 
android:text="@{Integer.toString(result.awayTeam.goals)}"/> 
</LinearLayout> 
</LinearLayout> 
</layout>

14
 
 
@Override 
 
binding = DataBindingUtil.setContentView(this, R.layout.match_result); 
 
binding.setResult(result); 
if 
}onCreate 
}activity

15
Code in XML?
Are you serious?!?

16
Complex code in XML is
NOT
a best practice

2Custom attributes

18
@BindingAdapter
<ImageView android:id="@+id/result_gif" style="@style/gif"/>
<ImageView style="@style/gif" app:imageUrl="@{result.gifUrl}"/>
@BindingAdapter("imageUrl") 
public static void loadImage(ImageView view, String url) { 
Glide.with(view.getContext()).load(url) 
.placeholder(R.drawable.loading).into(view); 
}

19
 
 
@Override 
 
binding = DataBindingUtil.setContentView(
this, R.layout.match_result); 
 
binding.setResult(result); 
}onCreate 
}activity

Annotated methods are static but…
@BindingAdapter("something") 
public static void bindSomething(View view, AnyObject b) { 
MyBinding binding = DataBindingUtil.findBinding(view);
 
MyObject myObject = binding.getMyObject(); 
//…
TextView myTextView =  
binding.myTextView;
//…
}
Can be any object
Get the layout binding
Get the connected objects
Access to all the views
Can be defined anywhere Can be used everywhere
Can be any View

@BindingAdapter("goals") 
public static void bindGoals(TextView view, int goals) { 
view.setText(Integer.toString(goals)); 
}__ 
21
BindingAdapter
android:text="@{Integer.toString(result.awayTeam.goals)}"/>
<TextView style="@style/goals"
app:goals="@{result.awayTeam.goals}"/>

3Components

23
<layout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto"> 
<data> 
<variable name="result" 
</data> 
<ImageView style="@style/gif" app:imageUrl="@{result.gifUrl}"/> 
 
 
android:text="@{result.awayTeam.name}"/> 
app:goals="@{result.awayTeam.goals}"/> 
</LinearLayout> 
</LinearLayout> 
</layout>
android:text="@{result.homeTeam.name}"/> 
app:goals="@{result.homeTeam.goals}"/> 
</LinearLayout>

24
<layout
xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto"> 
</layout>
team_detail.xml
<data> 
<variable name="team" 
type="it.droidcon.databinding.TeamScore"/> 
</data> 
android:text="@{team.name}"/> 
app:goals="@{team.goals}"/> 
</LinearLayout>

</data> 
<ImageView style="@style/gif" app:imageUrl="@{result.gifUrl}"/> 
 
 
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:bind="http://schemas.android.com/tools"> 
<data> 
<variable name="result" 
<include layout="@layout/team_detail" 
/>
/>
</LinearLayout> 
</layout>
bind:team="@{result.homeTeam}"
bind:team="@{result.awayTeam}"

4Two Way Data Binding

28
public class QuestionInfo { 
public String answer = ""; 
public int countdown = 10;
public int decrementCountdown() { 
return --countdown; 
}_
}_

29
}_
}_
<layout xmlns:android="http://schemas.android.com/apk/res/android"> 
<data> 
<variable 
name="info" 
type="it.droidcon.databinding.question.QuestionInfo"/> 
</data> 
 
<LinearLayout style="@style/form_root"> 
<TextView style="@style/question"/> 
 
<EditText style="@style/answer"  
android:text="@{info.answer}" /> 
 
<Button style="@style/form_button" 
android:enabled="@{info.countdown > 0 && !info.answer.empty}"/> 
 
<TextView style="@style/countdown" 
android:text="@{Integer.toString(info.countdown)}" /> 
</LinearLayout> 
</layout>

public class QuestionActivity extends AppCompatActivity { 
private QuestionInfo info; 
 
@Override 
protected void onCreate(@Nullable Bundle savedInstanceState) { 
QuestionBinding binding =
DataBindingUtil.setContentView(this, R.layout.question); 
info = new QuestionInfo(); 
binding.setInfo(info);
Handler handler = new Handler(); 
handler.postDelayed(new Runnable() { 
@Override public void run() { 
int newValue = info.decrementCountdown(); 
if (newValue > 0) { 
handler.postDelayed(this, 1000); 
} 
} 
}, 1000); 
}
}
30
}_
}_

32
Views are not automatically updated :(
package android.databinding; 
 
public interface Observable { 
 
void addOnPropertyChangedCallback(
OnPropertyChangedCallback callback); 
 
void removeOnPropertyChangedCallback(
OnPropertyChangedCallback callback); 
 
abstract class OnPropertyChangedCallback { 
public abstract void onPropertyChanged(
Observable sender, int propertyId); 
} 
}

34
public class QuestionInfo extends BaseObservable {_ 
private String answer = ""; 
 
private int countdown = 10; 
 
--countdown; 
notifyPropertyChanged(BR.countdown); 
return countdown; 
}__ 
 
@Bindable public String getAnswer() { 
return answer; 
}getAnswer 
 
public void setAnswer(String answer) { 
this.answer = answer; 
notifyPropertyChanged(BR.answer); 
}setAnswer 
 
@Bindable public int getCountdown() { 
}getCountdown 
}___

35
public class QuestionInfo {_ 
public final ObservableField<String> answer = new ObservableField<>(""); 
 
public final ObservableInt countdown = new ObservableInt(10); 
 
int value = countdown.get() - 1; 
countdown.set(value); 
return value; 
}__ 
}___

<data> 
<variable 
name="info" 
</data> 
 
 
android:text="@{info.answer}" /> 
 
 
</LinearLayout> 
</layout>
36
ObservableField<String>
ObservableInt
ObservableInt
 
 
return value; 
}__ 
}___
ObservableField<String>

38
Two way Data Binding
@BindingAdapter("binding") 
public static void bindEditText(EditText view,
final ObservableString observable) { 
Pair<ObservableString, TextWatcherAdapter> pair =
(Pair) view.getTag(R.id.bound_observable); 
if (pair == null || pair.first != observable) { 
if (pair != null) 
view.removeTextChangedListener(pair.second); 
TextWatcherAdapter watcher = new TextWatcherAdapter() { 
@Override
public void onTextChanged(CharSequence s, int a, int b, int c) { 
observable.set(s.toString()); 
} 
}; 
view.setTag(R.id.bound_observable, new Pair<>(observable, watcher)); 
view.addTextChangedListener(watcher); 
} 
String newValue = observable.get(); 
if (!view.getText().toString().equals(newValue)) 
view.setText(newValue); 
} 
medium.com/@fabioCollini/android-data-binding-f9f9d3afc761

<data> 
<variable 
name="info" 
</data> 
 
 
android:text="@={info.answer}" /> 
 
 
</LinearLayout> 
</layout>
40
Two way data binding

43
Layout
QuestionInfo
Binding
TextWatcherset(…)
addOnProperty
ChangedCallbackset(…)
if (changed)
WeakReference
if (changed)

5Data Binding + RxJava

45
<data> 
<variable 
name="info" 
</data> 
 
 
android:text="@={info.answer}" /> 
 
 
</LinearLayout> 
</layout>

public class QuestionInfo extends BaseObservable {_ 
private String answer = ""; 
private int countdown = 10; 
 
--countdown; 
notifyPropertyChanged(BR.countdown);
notifyPropertyChanged(BR.sendEnabled); 
}__ 
 
@Bindable public String getAnswer() { 
return answer; 
}getAnswer 
 
public void setAnswer(String answer) { 
this.answer = answer; 
notifyPropertyChanged(BR.answer); 
notifyPropertyChanged(BR.sendEnabled); 
}setAnswer 
 
@Bindable public int getCountdown() { 
}getCountdown
@Bindable public boolean isSendEnabled() { 
return !answer.isEmpty() && countdown > 0; 
}isButtonEnabled 
}___

47
Not an Observable, View is not updated!
 
 
return value; 
}__
public boolean isSendEnabled() { 
return !answer.get().isEmpty() && countdown.get() > 0; 
} 
}___

ObservableField<T> rx.Observable<T>

50
ObservableField<T> rx.Observable<T>
public static <T> rx.Observable<T> toRx(ObservableField<T> observableField) { 
return rx.Observable.fromEmitter(emitter -> { 
emitter.onNext(observableField.get()); 
OnPropertyChangedCallback callback = new OnPropertyChangedCallback() { 
@Override 
public void onPropertyChanged(Observable observable, int i) { 
emitter.onNext(((ObservableField<T>) observable).get()); 
} 
}; 
observableField.addOnPropertyChangedCallback(callback); 
emitter.setCancellation(() ->
observableField.removeOnPropertyChangedCallback(callback)); 
}, Emitter.BackpressureMode.BUFFER); 
}

51
 
public final ObservableInt countdown = new ObservableInt(10);
public final ObservableBoolean sendEnabled = new ObservableBoolean(); 
 
return value; 
}__
}___

52
 
 
private Subscription subscription; 
 
@Override 
//... 
} 
 
@Override protected void onStart() { 
super.onStart(); 
subscription = Observable.combineLatest( 
toRx(info.answer), 
toRx(info.countdown), 
(answer, countdown) -> 
!answer.isEmpty() && countdown > 0 
).subscribe(info.sendEnabled::set); 
} 
 
@Override protected void onStop() { 
super.onStop(); 
subscription.unsubscribe(); 
} 
}

53
compile 'com.cantrowitz:rxbroadcast:1.0.0'
public class ConnectionChecker { 
 
private Context context; 
 
public ConnectionChecker(Context context) { 
this.context = context; 
} 
 
public Observable<Boolean> getConnectionStatus() { 
IntentFilter filter = new IntentFilter(
ConnectivityManager.CONNECTIVITY_ACTION); 
return RxBroadcast.fromBroadcast(context, filter) 
.map(i -> getNetworkInfo()) 
.map(info -> info != null && info.isConnected()) 
.distinctUntilChanged(); 
} 
 
private NetworkInfo getNetworkInfo() { 
ConnectivityManager connectivityManager = (ConnectivityManager)
context.getSystemService(Context.CONNECTIVITY_SERVICE); 
return connectivityManager.getActiveNetworkInfo(); 
} 
}

 
 
private Subscription subscription; 
 
@Override 
//... 
}onCreate 
 
@Override protected void onStart() { 
super.onStart(); 
subscription = Observable.combineLatest( 
toRx(info.answer), 
toRx(info.countdown), 
connectionChecker.getConnectionStatus(), 
(answer, countdown, connected) -> 
!answer.isEmpty() && countdown > 0 && connected 
).subscribe(info.sendEnabled::set); 
}onStart 
 
@Override protected void onStop() { 
super.onStop(); 
subscription.unsubscribe(); 
}onStop 
}_
54

6MVVM

56
MatchResultViewModel
public class MatchResultViewModel {
 
public final ObservableField<MatchResult> result =
new ObservableField<>(); 
 
public final ObservableBoolean loading =
new ObservableBoolean(); 
 
public void reload() {
loading.set(true); 
reloadInBackground(result -> { 
loading.set(false); 
this.result.set(result); 
}); 
} 
}

xmlns:app="http://schemas.android.com/apk/res-auto"
<data> 
<variable name="viewModel" 
type="it.droidcon.databinding.MatchResultViewModel"/> 
</data> 
<ImageView style="@style/gif"
app:imageUrl="@{viewModel.result.gifUrl}"/> 
 
 
/>
/>
</LinearLayout> 
</layout>
bind:team="@{viewModel.result.homeTeam}"
bind:team="@{viewModel.result.awayTeam}"
ObservableField

58
Visibility
<FrameLayout style="@style/progress_layout" 
android:visibility=
"@{viewModel.loading ? View.VISIBLE : View.GONE}"> 
<ProgressBar style="@style/progress"/> 
</FrameLayout>
xmlns:app="http://schemas.android.com/apk/res-auto" 
<data>
<import type="android.view.View"/> 
<variable name="viewModel" 
type="it.droidcon.databinding.MatchResultViewModel"/>
</data> 
<FrameLayout style="@style/main_container">
 
 
</LinearLayout> 
 
 
</FrameLayout> 
</layout>

59
Visibility
app:visibleOrGone="@{viewModel.loading}"> 
</FrameLayout>
@BindingAdapter("visibleOrGone") 
public static void bindVisibleOrGone(View view, boolean b) { 
view.setVisibility(b ? View.VISIBLE : View.GONE); 
}____
@BindingAdapter("visible") 
public static void bindVisible(View view, boolean b) { 
view.setVisibility(b ? View.VISIBLE : View.INVISIBLE); 
}

android:onClick="@{???}"> 
 
</LinearLayout> 
60
}___
public class MatchResultViewModel {
public final ObservableField<MatchResult> result =
new ObservableField<>(); 
public final ObservableBoolean loading = new ObservableBoolean(); 
loading.set(true); 
reloadInBackground(result -> { 
loading.set(false); 
this.result.set(result); 
}); 
}__

android:onClick="@{v -> viewModel.reload()}"> 
 
</LinearLayout> 
61
//.. 
}__
android:onClick=“@{viewModel::reload}”> 
 
</LinearLayout> 
public void reload(View v) {
//.. 
}__
@BindingAdapter("android:onClick") 
public static void bindOnClick(View view, final Runnable listener) { 
view.setOnClickListener(new View.OnClickListener() { 
@Override public void onClick(View v) { 
listener.run(); 
}____ 
}); 
}___
 
</LinearLayout> 
//.. 
}__

62
Final layout
xmlns:app="http://schemas.android.com/apk/res-auto" 
<data> 
 
</data> 
<FrameLayout style="@style/main_container">
 
 
</LinearLayout> 
 
app:visibleOrGone="@{viewModel.loading}"> 
</FrameLayout> 
 
</FrameLayout> 
</layout>

63
Model View ViewModel
View
ViewModel
Model
DataBinding
Retained on
configuration change
Saved in Activity or
Fragment state
Activity or Fragment

MVVM
View
ViewModel
Model
DataBinding
View
Presenter
Model
MVPVs

MVVM MVPVs
Less Java code
if (view != null)
A/B testing on View
Sometimes we need an
Activity :(
Testable code Testable code
Less XML
No more

66
github.com/fabioCollini/LifeCycleBinder
Move your Android code to testable Java classes

Custom attributes Reusable UI code
67
Data binding
Includes UI components
RxJava Easy composition

68
Links
developer.android.com/tools/data-binding/guide.html
Google I/O 2015 - What's new in Android
Data Binding -- Write Apps Faster (Android Dev Summit 2015)
Advanced Data Binding - Google I/O 2016
George Mount medium profile
Radosław Piekarz: RxJava meets Android Data Binding
Florina Muntenescu: A Journey Through MV Wonderland
Bill Phillips: Shades of MVVM

69
Thanks for your attention!
Questions?
This presentation will be soon available on the droidcon London website at
uk.droidcon.com/#skillscasts

Android Data Binding in action using MVVM pattern - droidconUK

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