DialogEventBus.java

public enum DialogEventBus {
  OK,
  CANCEL,
  CLOSE,
  ;

  private final SerializedSubject<String, String> bus;

  DialogEventBus() {
    bus = new SerializedSubject<>(PublishSubject.create());
  }

  public void post(String tag) {
    bus.onNext(tag);
  }

  public Observable<String> toObservable(String tag) {
    return bus.filter(s -> TextUtils.equals(s, tag));
  }

  public boolean hasObservers() {
    return bus.hasObservers();
  }
}