Managing RxState Starting 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) {
    bind();
  }

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

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

  /** on creation */
  public Observable<Intent.LoadFirstPageIntent> loadFirstPageIntent() {}

  /** on bottom of list */
  public Observable<Intent.LoadNextPageIntent> loadNextPageIntent() {}

  public void render(ViewState state) {
    // Update the UI
  }
}

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 Service service;

  Binder(Service service) {
    this.service = service;
  }
  
  Observable<ViewState> compose(Observable<Intent> intents) {
    return intents
        .map(this::actionFromIntent)
        .compose(actionToResultTransformer)
        .scan(ViewState.idle(), reducer);
  }

  // Emits loading, success and failure events.
  private ObservableTransformer<Action.LoadFirstPageAction, Result.LoadFirstPageResult>
      loadFirstPageTransformer;

  // Emits loading, success and failure events.
  private ObservableTransformer<Action.LoadNextPageAction, Result.LoadNextPageResult>
      loadNextPageTransformer;

  private ObservableTransformer<Action, Result> actionToResultTransformer =
      actions -> actions.publish(shared -> Observable.merge(
          shared.ofType(Action.LoadFirstPageAction.class).compose(loadFirstPageTransformer),
          shared.ofType(Action.LoadNextPageAction.class).compose(loadNextPageTransformer));

  private Action actionFromIntent(Intent intent) {
    // Create an Action from an Intent. 
  }

  private static BiFunction<ViewState, Result, ViewState> reducer =
      (previousState, result) -> {
        // Create new state from previousState
        // Update the new state accordingly to the result
        // Return it
      };
}