RxJava - How to take the first element of a list and return it as Observable

问题

Let's take this observable:

Observable<List<UserProfile>> findUser =service.getUserProfiles()

How can I transform it so it returns the first element as an Observable (and not an Observable list just containing the first element). I tried first() and takeFirst() but it still returns a list.

回答1:

Map it!

Observable<List<UserProfile>> findUser = service.getUserProfiles();
Observable<UserProfile> firstUser = findUser
    .filter(list -> !list.isEmpty())
    .map(list -> list.get(0));

回答2:

Without see what´s going on getUserProfile() it´s complicated, but what about this

@Test
public void getFirstUser(){
    Observable<List<Integer>> findUser =Observable.just(Arrays.asList(1,2,3));
    Observable<Integer> user = findUser
            .flatMap(Observable::from)
            .first();
    user.subscribe(System.out::println);
}

来源：https://stackoverflow.com/questions/38212442/rxjava-how-to-take-the-first-element-of-a-list-and-return-it-as-observable