Binding Data with Android Databinding +Riccardo Ciovati 

Whoami ● I have been building Android apps for more than 5 years ● Android Developer at Subito ● GDG Milano manager since April 2015 

Data Binding is a way to get your data from your data model into your UI using (almost) just markup. What’s Data Binding? 

How we did it so far? 

How we did it so far? public class MainActivity extends AppCompatActivity { private Ad mAd = new Ad("iPhone for sale"); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); TextView subject = (TextView) findViewById(R.id.ad_subject); subject.setText(mAd.getSubject()); } } 

What’s wrong with this? ● Could crash at runtime ○ Missing ID ○ Wrong cast ○ Multiple layout configurations can have different elements ● Each findViewById requires a layout traversal ● Only the main thread can access those elements ● It’s boilerplate code ○ A few libraries to the rescue (eg Butterknife) 

Hello Data Binding 

Hello Data Binding public class MainActivity extends AppCompatActivity { private Ad mAd = new Ad("iPhone for sale"); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main); binding.setAd(mAd); } } 

Hello Data Binding ● ● ● ● ● ● ● ● Code generator + small runtime dependency ● Works with API level 7+ apply plugin: 'com.android.databinding' buildscript { repositories { jcenter() } dependencies { classpath "com.android.databinding:dataBinder:1.0-rc2" } } 

● Most Java expressions are supported: ○ String concatenation: + ○ Logical operator: &&, || ○ Comparision: ==, =>, <=, ect ● Method invocation and field access ● Built-in null-safety and null-coalescing operator: ○ android:text="@{ad.subject ?? @string/no_subject}" ● Expressions autocomplete in AS is not supported (yet) ● Syntax checks at compile-time Full List: https://goo.gl/9FVASg Expressions - Basics 

Expressions - Method invocation 

Expressions - Arrays and Maps android:text="@{list[index]}" android:text="@{sparse[index]}" android:text="@{map[key]}" 

Expressions - Considerations ● Expression type matters! ● Avoid complex expressions ○ Consider use ViewModel 

Model-View-ViewModel is an architectural pattern which allows to to separate and mediate the communication between model and views. ● Separation of presentation logic and business logic ● Testability Source: https://goo.gl/d0oxj7 MVVM MVVM picture 

One way: model values are automatically assigned to the UI placeholder elements specified through the data binding notation, but the UI elements don't change the values in the model. Changes in the model are not propagated to the view. Source: https://goo.gl/fo3797 Databinding models One-Way Data Binding 

Two way: model values are automatically assigned to the UI placeholder elements specified through the data binding notation. Any changes to the view are immediately reflected in the model, and any changes in the model are propagated to the view. Source: https://goo.gl/fo3797 Databinding models Two-Way Data Binding 

One and a half way databinding The Data Binding Library provides a mechanism to implement an hybrid approch between one-way and two-way databinding in wich model changes are reflected to the UI. To implement that we have two options: ● Using Observable Objects ● Using Observable Fields 

Observable Objects public class Ad extends BaseObservable { private String mSubject; public void setSubject(String subject) { mSubject = subject; notifyPropertyChanged(BR.subject); } @Bindable public String getSubject() { return mSubject; } } 

Observable Objects ● We need to annotate each getter with the @Bindable annotation provided by the Data Binding Library and notify the changes in the setter. ● For each method annotated the compiler will generate a corrisponding field in the BR class. If case we don’t want or we can’t extend from BaseObservable we can implement the Observable interface. 

Observable Fields ● Built-in Observable types: ObservableField, ObservableBoolean, ObservableByte, ObservableChar, ObservableShort, ObservableInt, ObservableLong, ObservableFloat, ObservableDouble, and ObservableParcelable. public class Ad { public final ObservableField subject = new ObservableField<>(); } //Setting the value will refresh the components observing this field mAd.subject.set("iPhone for sale"); 

Observable Collections ● ObservableList ○ ObservableArrayList is the implementation ○ Notify whether items are added, changed, moved or removed ● ObservableMap ○ ObservableArrayMap is the implementation ○ Notify whether a key is added, removed or changed. 

● You don’t have to take care to set Observables fields from the main thread, the Data Binding Library will dispatch notifications in the main thread for you. Observable Fields 

Binding Adapter ● ● ● ● ● ● ● 

Binding Adapter ● ● ● ● ● ● ● 

Binding Adapter ● Namespace is actually not taken into account ● Cool examples: ○ Setting custom typeface: https://goo.gl/H9v1vA ○ Binding collection to ListView/RecyclerView: https://goo.gl/zQl94z @BindingAdapter("bind:displayedChild") public static void setDisplayedChild(ViewAnimator viewAnimator, int index) { viewAnimator.setDisplayedChild(index); } 

Binding Adapter ● You read parameters from multiple attributes at once @BindingAdapter({"bind:imageUrl", "bind:error"}) public static void loadImage(ImageView view, String url, Drawable error) { Picasso.with(view.getContext()).load(url).error(error).into(view); } 

Summary ● Databinding allows you to rethink your app architecture in a more robust and testable way ● Keep away your business logic from you views → MVVM ● Tools are currently under development so expect big enhacements in the future 

Thanks! We are hiring! - jobs.subito.it 

References and further reading ● Databinding Guide: https://goo.gl/2s693c ● Building Apps Faster with Android Data Binding: https://goo.gl/zkyNwA ● Data Binding Techniques @ Droidcon NYC, 2015: https://goo.gl/WsmIYc ● Android Databinding: goodbye Presenter, hello ViewModel: http://goo. gl/xnqDWt ● MVVM on Android using the Data Binding Library: http://goo.gl/qCXFRc