RxJava and RxBinding

Overview

One of the benefits of using RxJava is the ability to compose asynchronous events in a more straightforward way. Complex UI interactions in Android can also be greatly simplified too, especially when there are multiple UI events that can trigger. To describe the interaction pattern with standard Android code, you would usually need to use a combination of both listeners, Handlers and AsyncTask (see this ebook for an example). With RxJava and RxBinding, this logic can be greatly simplified and you can describe the interaction patterns between multiple UI components.

Setup

Make sure to follow the setup instructions for RxJava first.

To use RxBinding in your project, add the following line to your module level build.gradle file:

compile 'com.jakewharton.rxbinding:rxbinding:0.4.0'

If you rely on any widgets from the 'support-v4' library bindings, make sure to add the following:

compile 'com.jakewharton.rxbinding:rxbinding-support-v4:0.4.0'

You may also need to add any widgets that rely on the 'appcompat-v7' library:

compile 'com.jakewharton.rxbinding:rxbinding-appcompat-v7:0.4.0'

Check out this link to learn more about RxBinding.

Converting to Observables

You can use the RxJava to convert Android view events to Observables. Essentially the library wraps the listener and implements the Observable interface as described in this section.

Normally we react to a click event on Android like the following example:

Button button = (Button)findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
      //handle on click here
   }
});

Using RxBinding, same can be accomplished with RxJava subscription:

Button button = (Button)findViewById(R.id.button);
Subscription buttonSub = RxView.clicks(button).subscribe(new Action1<Void>() {
   @Override
   public void call(Void aVoid) {
      //handle on click here
   }
}); 

// make sure to unsubscribe the subscription.

Another example handling text change on an EditText. Vanila android:

EditText editText = (EditText)findViewById(R.id.editText);
editText.addTextChangedListener(new TextWatcher() {
   @Override
   public void beforeTextChanged(CharSequence s, int start, int count, int after) {
   
   }
   
   @Override
   public void onTextChanged(CharSequence s, int start, int before, int count) {
      // do some work with new text
   }
   
   @Override
   public void afterTextChanged(Editable s) {
   
   }
});

Same thing written with RxBinding support:

EditText editText = (EditText)findViewById(R.id.editText);
Subscription editTextSub = RxTextView.textChanges(editText).subscribe(new Action1<CharSequence>() {
   @Override
   public void call(CharSequence value) {
      // do some work with new text
   }
});

// make sure to unsubscribe the subscription.

Example

For example, consider what you would need to do to implement a SearchView that will trigger an API call to fetch results related to the search term, so long as the term is at least three characters long and there has been at least a 100 milliseconds delay since the user last modified the search term in the view. With RxJava, this pattern can be described as follows:

RxTextView.textChanges(searchTextView)
	.filter(new Func1<String, Boolean> (){
		@Override
		public Boolean call(String s) {
			return s.length() > 2;
		}
	})
	.debounce(100, TimeUnit.MILLISECONDS)
	.switchMap(new Func1<String, Observable<List<Result>>>() {
		makeApiCall(s);
	})
	.subscribeOn(Schedulers.io())
	.observeOn(AndroidSchedulers.mainThread())
	.subscribe(/* attach observer */);

The filter operation will only trigger if there is more than 2 characters, the debounce operation will filter multiple events that occur within 100 ms, and the switchMap operation will return an API response in the form of another Observable to make the API call. SwitchMap is preferred over FlatMap because it ignores stale response - http://stackoverflow.com/questions/28175702/what-is-the-difference-between-flatmap-and-switchmap-in-rxjava

Attribution

This guide was originally drafted by Adegeye Mayowa.

References

• http://www.oreilly.com/programming/free/files/rxjava-for-android-app-development.pdf