Chain two retrofit observables w/ RxJava

Question

I want to execute 2 network calls one after another. Both network calls return Observable. Second call uses data from successful result of the first call, method in successf

Answer 1

Have you looked into flatMap()? If your aversion to it (or zip()) is the need to make an unnecessary class just to hold two objects, android.util.Pair might be an answer. I'm not sure how to get exactly the error handling you're looking for, though.

       API().auth(email, password)
        .subscribeOn(Schedulers.newThread())
        .observeOn(AndroidSchedulers.mainThread())
        .flatMap(new Func1<AuthResponse, Observable<List<User>>>() {
          @Override
          public Observable<List<User>> call(AuthResponse authResponse) {
            return API().getUser(authResponse.getAccessToken());
          }
        }, new Func2<AuthResponse, List<User>, Pair<AuthResponse, List<User>>>() {
          @Override
          public Pair<AuthResponse, List<User>> call(AuthResponse authResponse, List<User> users) {
            return new Pair<>(authResponse, users);
          }
        }).subscribe(new Action1<Pair<AuthResponse, List<User>>>() {
          @Override
          public void call(Pair<AuthResponse, List<User>> pair) {
            doSomething(pair.first, pair.second);
          }
        }, new Action1<Throwable>() {
          @Override
          public void call(Throwable throwable) {
            // not sure how to tell which one threw the error
          }
        });

Answer 2

In addition to Anthony R.'s answer, there is a flatMap overload which takes a Func2 and pairs your primary and flattened values for you. In addition, look at the onErrorXXX and onExceptionXXX operators for error manipulation, and chain them with your first and second Observables

first.onErrorReturn(1)
.flatMap(v -> service(v).onErrorReturn(2), (a, b) -> a + b);