The RxJava Android Module

The rxjava-android module contains Android-specific bindings for RxJava. It adds a number of classes to RxJava to assist in writing reactive components in Android application.

• It provides a Scheduler that schedules an Observable on a given Android Handler thread, particularly the main UI thread.
• It provides base Observer implementations that make guarantees concerning reliable and thread-safe use throughout Fragment and Activity life-cycle callbacks. (coming soon)
• It provides reusable, self-contained, reactive components for common Android use cases and UI concerns. (coming soon)

Binaries

You can find binaries and dependency information for Maven, Ivy, Gradle and others at http://search.maven.org.

Here is an example for Maven:

<dependency>
    <groupId>com.netflix.rxjava</groupId>
    <artifactId>rxjava-android</artifactId>
    <version>0.10.1</version>
</dependency>

…and for Ivy:

<dependency org="com.netflix.rxjava" name="rxjava-android" rev="0.10.1" />

Examples

Observing on the UI thread

You commonly deal with asynchronous tasks on Android by observing the task’s result or outcome on the main UI thread. Using vanilla Android, you would typically accomplish this with an AsyncTask. With RxJava you would instead declare your Observable to be observed on the main thread by using the observeOn operator:

    public class ReactiveFragment extends Fragment {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Observable.from("one", "two", "three", "four", "five")
                .subscribeOn(Schedulers.newThread())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(/* an Observer */);
    }

This executes the Observable on a new thread, which emits results through onNext on the main UI thread.

Observing on arbitrary threads

The previous example is a specialization of a more general concept: binding asynchronous communication to an Android message loop by using the Handler class. In order to observe an Observable on an arbitrary thread, create a Handler bound to that thread and use the AndroidSchedulers.handlerThread scheduler:

    new Thread(new Runnable() {
        @Override
        public void run() {
            final Handler handler = new Handler(); // bound to this thread
            Observable.from("one", "two", "three", "four", "five")
                    .subscribeOn(Schedulers.newThread())
                    .observeOn(AndroidSchedulers.handlerThread(handler))
                    .subscribe(/* an Observer */)
                    
            // perform work, ...
        }
    }, "custom-thread-1").start();

This executes the Observable on a new thread and emits results through onNext on custom-thread-1. (This example is contrived since you could as well call observeOn(Schedulers.currentThread()) but it illustrates the idea.)

See also

• The rxjava-android readme file
• Functional Reactive Programming on Android With RxJava and Conquering concurrency - bringing the Reactive Extensions to the Android platform by Matthias Käppler
• Learning RxJava for Android by example by Kaushik Gopal
• Top 7 Tips for RxJava on Android and Rx Architectures in Android by Timo Tuominen
• FRP on Android by Yaroslav Heriatovych
• Rx for .NET and RxJava for Android by Olli Salonen
• RxJava in Xtend for Android by Andre Medeiros
• RxJava and Xtend by Stefan Oehme