Databinding in Android BRYAN HERBST

Job Interview Q: How does an Android Activity fit in to the MVC pattern? A: Ehh…

MV[C|P|VM] A Model that represents your raw data. Aka POJOs. A View that dictates how your data is displayed to the user Something to get the data and display the view

View

Controller var template = Handlebars.compile(viewTemplate); var data = {title: “Hello World", body: “Templating rocks!"}; var html = template(data);

Let there be data binding Now we can have better separation of concerns Activities and Fragments now have more limited scope and a clearer purpose: ◦ Load data ◦ Bind data to the View ◦ Respond to events

Setup buildscript { dependencies { classpath 'com.android.databinding:dataBinder:1.0-rc0' } } apply plugin: 'com.android.databinding'

The View- step one Wrap your layout in a tag

The View- step two Add a tag with s for your models

The View- step three Bind to model with @{model.property}

The binding class Plugin generates binding class my_fancy_layout.xml becomes MyFancyLayoutBinding

The controller side @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ActivityAnimalBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_animal); binding.setAnimal(new Elephant()); }

Demo time!

Can the views be smarter? What else can we bind?

Visibility- step one Import types into layouts just like Java

Visibility- step two android:visibility="@{note.content == null ? View.GONE : View.VISIBLE}"

Introducing the ViewModel Because that date format is terrible.

NoteViewModel public class NoteViewModel { private static final DateFormat TIMESTAMP_FORMAT = DateFormat.getDateInstance(); private Note mNote; public String getFormattedTimestamp() { return TIMESTAMP_FORMAT.format(mNote.getCreatedTime()); } }

Demo time!

Data binding: Two way street Using app namespace, bind to anything with a setter

Automatic updates What happens when our data changes?

Observables No, not RxJava

Observables in the ViewModel public ObservableInt numClicks; public View.OnClickListener clickListener = new View.OnClickListener() { @Override public void onClick(View view) { numClicks.set(numClicks.get() + 1); } };

Observables in the layout Text now automatically updates

Demo time!

Resources https://developer.android.com/tools/data-binding/guide.html Tons of information about: ◦ s ◦ Operators in bindings ◦ Accessing arrays/lists/maps ◦ Using resources in bindings ◦ Value converters ◦ Binding custom view properties ◦ More ways to make data observable