RxGroups

Easily group RxJava Observables together and tie them to your Android Activity lifecycle

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Felipe Lima

Felipe Lima

RxGroups

Build Status

RxGroups lets you group RxJava Observables together in groups and tie them to your Android lifecycle. This is especially useful when used with Retrofit.

For simple scenarios you can probably just let the original request be cancelled and fire a new one. However it’s easy to see how this becomes a problem in more complex situations.

Let’s say your user is submitting a payment. You’ll probably want to to guarantee that you can reattach to the same in-flight or completed request after rotating the screen or leaving the Activity and returning later.

RxGroups will also automatically prevent events from being delivered to your Activity or Fragment before onResume() and after onPause(). If that happens, they will be automatically cached in memory and delivered once the user returns to your screen. If they never return, the memory is then reclaimed automatically after onDestroy().

Usage

  1. Add a GroupLifecycleManager field to your Activity, Fragment, Dialog, etc. and call its respective lifecycle methods according to your own (eg.: onPause, onResume, onDestroy, etc.);
  2. Annotate your ResubscriptionObserver with @AutoResubscribe and use method resubscriptionTag() to tell RxGroups what tag it should use for reattaching your Observer to it Observable automatically.
  3. Before subscribing to your Observable, compose it with observableGroup.transform() to define a tag for that Observable;

Example

public class MyActivity extends Activity {
  private static final String OBSERVABLE_TAG = "arbitrary_tag";
  private TextView output;
  private FloatingActionButton button;
  private GroupLifecycleManager groupLifecycleManager;
  private ObservableGroup observableGroup;
  private Observable<Long> observable = Observable.interval(1, 1, TimeUnit.SECONDS);

  // The Observer field must be public, otherwise RxGroups can't access it
  @AutoResubscribe public final ResubscriptionObserver<Long> observer = new ResubscriptionObserver<Long>() {
    @Override public void onCompleted() {
      Log.d(TAG, "onCompleted()");
    }

    @Override public void onError(Throwable e) {
      Log.e(TAG, "onError()", e);
    }

    @Override public void onNext(Long l) {
      output.setText(output.getText() + " " + l);
    }

    @Override public Object resubscriptionTag() {
      return OBSERVABLE_TAG;
    }
  };

  @Override protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    output = (TextView) findViewById(R.id.txt_output);
    button = (FloatingActionButton) findViewById(R.id.fab);
    SampleApplication application = (SampleApplication) getApplication();
    ObservableManager manager = application.observableManager();
    groupLifecycleManager = GroupLifecycleManager.onCreate(manager, savedInstanceState, this);
    observableGroup = groupLifecycleManager.group();

    button.setOnClickListener(v -> observable
        .compose(observableGroup.<Long>transform(OBSERVABLE_TAG))
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(observer));
  }

  @Override protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    groupLifecycleManager.onSaveInstanceState(outState);
  }

  @Override protected void onResume() {
    super.onResume();
    groupLifecycleManager.onResume();
  }

  @Override protected void onPause() {
    super.onPause();
    groupLifecycleManager.onPause();
  }

  @Override protected void onDestroy() {
    super.onDestroy();
    groupLifecycleManager.onDestroy(this);
  }
}

Optional: If you don’t want to use a ResubscriptionObserver with @AutoResubscribe just use a regular Observer anonymous class with a public method called resubscriptionTag(). Eg.:

@AutoResubscribe public final Observer<Long> observer = new Observer<Long>() {
    @Override public void onCompleted() {
    }

    @Override public void onError(Throwable e) {
    }

    @Override public void onNext(Long l) {
    }

    public Object resubscriptionTag() {
      return Arrays.asList("tag1", "tag2", "tag3");
    }
  };

If the method doesn’t exist or is not public, RxGroups will throw a RuntimeException letting you know. You can use any Object tag for your Observer, including arrays and List, In that case, it will associate the Observer with all the tags in the collection, allowing you to share the same Observer with multiple Observables.

Download with Gradle

compile 'com.airbnb:rxgroups-android:0.3.5'

Check out the Sample app for more details and a complete example!

Snapshots of the development version are available in Sonatype’s snapshots repository.

Felipe Lima

Felipe Lima

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