CODEWITHSUNDEEP
androidrx-javarx-android
Ralph Bergmann
Ralph Bergmann

Reputation: 3076

flatMap which returns the item and the result of the transformation

I have a not so beautiful RxJava flow :-(

RxView.clicks(sendButton)
      .flatMap(ignored -> cameraManager.getCamera())
      .flatMap(camera -> camera.isReachable())
      .filter(reachable -> reachable)
      .flatMap(ignored -> cameraManager.getCamera())
      .flatMap(camera -> camera.sendCommand("foo bar"))
      .subscribe(send -> Timber.i("send successful"),
                 error -> Timber.e(error, "send failed: "));

I don't like this chain of cameraManager.getCamera() to do something with the camera.

Is there a way that a flatMap returns both the item and the result of its transformation like this flatMap(camera -> Pair.create(camera, camera.isReachable()))?

RxView.clicks(sendButton)
      .flatMap(ignored -> cameraManager.getCamera())
      .flatMap(camera -> Pair.create(camera, camera.isReachable()))
      .filter(pair -> pair.second)
      .flatMap(pair -> pair.first.sendCommand("foo bar"))
      .subscribe(send -> Timber.i("send successful"),
                 error -> Timber.e(error, "send failed: "));

More code to understand my snippet:

private class Bar {

    private CameraManager cameraManager = new CameraManager();
    private View          sendButton    = null;

    public Bar() {
        bind();
    }

    private void bind() {

        RxView.clicks(sendButton)
              .flatMap(ignored -> cameraManager.getCamera())
              .flatMap(camera -> camera.isReachable())
              .filter(reachable -> reachable)
              .flatMap(ignored -> cameraManager.getCamera())
              .flatMap(camera -> camera.sendCommand("foo bar"))
              .subscribe(send -> Timber.i("send successful"),
                         error -> Timber.e(error, "send failed: "));
    }
}

private class CameraManager {

    public Observable<Camera> getCamera() {
        return Observable.just(new Camera());
    }
}

public class Camera {

    private BehaviorSubject<Boolean> reachable = BehaviorSubject.create(false);


    public Observable<Boolean> isReachable() {
        return reachable.asObservable();
    }

    public Observable<Boolean> sendCommand(String msg) {
        return Observable.create(subscriber -> {

            // send message...
            final boolean sendSuccessful = true;

            if (sendSuccessful) {
                subscriber.onNext(true);
                subscriber.onCompleted();
            } else {
                subscriber.onError(new Exception());
            }
        });
    }
}

Upvotes: 0

Views: 543

Answers (1)

akarnokd
akarnokd

Reputation: 70007

There is a flatMap overload that has an additional Func2<T, U, R> that takes the original element and each element the generated Observable<U> and returns a value to be emitted.

Observable.range(1, 10)
.flatMap(v -> Observable.range(1, 2), (v, w) -> v + 100 * w)
.subscribe(System.out.println);

Upvotes: 3

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