Managing RxState Ending point

01_Activity.java

/**
 * Many things are omitted to focus on the relevant data.
 */
public class Activity extends AppCompatActivity {
  Binder binder;

  @Override protected void onCreate(@Nullable Bundle savedInstanceState) {
    Object lastCustomNonConfigInstance = getLastCustomNonConfigurationInstance();
    if (lastCustomNonConfigInstance != null) {
      binder = (Binder) lastCustomNonConfigInstance;
    } else {
      binder = new Binder();
    }
    
    bind();
  }

  private void bind() {
    binder.getStatesAsObservable().subscribe(this::render);
    binder.forwardIntents(intents());
  }

  public Observable<Intent> intents() {
    return Observable.merge(loadFirstPageIntent(), loadNextPageIntent());
  }

  @Override public Object onRetainCustomNonConfigurationInstance() {
    return binder;
  }
}

02_Binder.java

/**
 * Many things are omitted to focus on the relevant data.
 * See Jake's talk for the flow explanation: http://jakewharton.com/the-state-of-managing-state-with-rxjava/
 */
class Binder {
  private PublishSubject<Intent> intentsSubject = PublishSubject.create();
  private PublishSubject<ViewState> statesSubject = PublishSubject.create();

  Binder() {
    compose().subscribe(state -> statesSubject.onNext(state));
  }

  private Observable<ViewState> compose() {
    return intentSubject
        .scan(intentReducer)
        .map(this::actionFromIntent)
        .compose(actionToResultTransformer)
        .scan(ViewState.idle(), reducer);
  }

  public void forwardIntents(Observable<Intent> intents) {
    intents.subscribe(intent -> IntentSubject.onNext(intent));
  }

  public PublishSubject<ViewState> getStatesAsObservable() {
    return statesSubject;
  }

  private BiFunction<Intent, Intent, Intent> intentReducer =
      (previousIntent, newIntent) -> {
        // i.e. we are inside the scan, meaning there has already
        // been intent in the past, meaning the InitialIntent cannot
        // be the first => it is a config change.
        if (newIntent instanceof Intent.InitialIntent) {
          return Intent.GetLastState.create();
        } else {
          return newIntent;
        }
      };
}