When should one use RxJava Observable and when simple Callback on Android?

Question

I\'m working on networking for my app. So I decided to try out Square\'s Retrofit. I see that they support simple Callback

@GET("/user/{id}/         


        

Answer 1

By the samples and conclusions in other answers, I think there is no big difference for simple one or two-steps tasks. However, Callback is simple and straightforward. RxJava is more complicated and too big for simple task. There is the third solution by: AbacusUtil. Let me implement above use cases with all three solutions: Callback, RxJava, CompletableFuture(AbacusUtil) with Retrolambda:

Fetch photo from network and save/display on device:

// By Callback
api.getUserPhoto(userId, new Callback() {
    @Override
    public void onResponse(Call call, Response response) {
        save(response.body()); // or update view on UI thread.
    }

    @Override
    public void onFailure(Call call, Throwable t) {
        // show error message on UI or do something else.
    }
});

// By RxJava
api.getUserPhoto2(userId) //
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(photo -> {
            save(photo); // or update view on UI thread.
        }, error -> {
            // show error message on UI or do something else.
        });

// By Thread pool executor and CompletableFuture.
TPExecutor.execute(() -> api.getUserPhoto(userId))
        .thenRunOnUI((photo, error) -> {
            if (error != null) {
                // show error message on UI or do something else.
            } else {
                save(photo); // or update view on UI thread.
            }
        });

Load user details and photo in parallel

// By Callback
// ignored because it's little complicated

// By RxJava
Observable.zip(api.getUserDetails2(userId), api.getUserPhoto2(userId), (details, photo) -> Pair.of(details, photo))
        .subscribe(p -> {
            // Do your task.
        });

// By Thread pool executor and CompletableFuture.
TPExecutor.execute(() -> api.getUserDetails(userId))
          .runOnUIAfterBoth(TPExecutor.execute(() -> api.getUserPhoto(userId)), p -> {
    // Do your task
});