Rxjava: 2.1.2 Completable with andThen never completes

[micHar]

This test fails:

Completable.complete()
        .andThen{ Completable.complete() }
        .test()
        .assertComplete()

However this one succeeds:

Completable.complete()
        .test()
        .assertComplete()

This one also succeeds:

    Flowable.just("")
            .flatMap { Flowable.just("") }
            .test()
            .assertComplete()

My understanding is that concating (which is what andThen does?) two completables which complete immediately should complete.
I tried:

• using awaitForTerminalEvent but it just runs forever in the first case.
• .andThen{} instead of .andThen{ Completable.complete() }
• Completable.fromCallable instead of Completable.complete() or switching from a Flowable to Completable

[JakeWharton]

You want andThen(Completable.complete()). Note the use of parenthesis and
not curly braces. The latter creates a lambda that doesn't call its emitter.

On Sat, Aug 12, 2017, 11:30 AM Michał Klimczak [e-mail]
wrote:

This test fails:

Completable.complete()
.andThen{ Completable.complete() }
.test()
.assertComplete()

However this one succeeds:

Completable.complete()
.test()
.assertComplete()

This one also succeeds:

Flowable.just("")
        .flatMap { Flowable.just("") }
        .test()
        .assertComplete()

My understanding is that concating (which is what andThen does?) two
completables which complete immediately should complete.
I tried:

• using awaitForTerminalEvent but it just runs forever in the first
  case.
• .andThen{} instead of .andThen{ Completable.complete() }
• Completable.fromCallable instead of Completable.complete() or
  switching from a Flowable to Completable

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[micHar]

So simple. Thanks!

[akarnokd]

Please be patient on StackOverflow (deleted) next time!

[micHar]

Generally I am, but it honestly looked like an error to me, especially given the way flatMap and similar operators work for Flowable. Sorry!

[afaucogney]

@micHar I agree with you, the .andThen{} is equivalent to .doOnComplete{}, isn't it? I mean what would be the use case that only .andThen{} solve ?

[amanshuraikwar]

I am having a similar problem:

someCompletable().andThen(someObservable()).subscribe{...}

my someObservable() is never being called. Please help! I am new to Rx.

On a similar note, how can I sequence an Observable after a Completable. Is that even possible?

[akarnokd]

@amanshuraikwar That is how it is supposed to be done. How is it not working. Could you write an unit test demonstrating your problem?

[amanshuraikwar]

Here is how I am using it:

Observable<Integer> observable = Observable.just(1).doOnSubscribe(disposable -> System.out.println("observable-subscribed"));

Completable completable = new Completable() {
    @Override
    protected void subscribeActual(CompletableObserver s) {
        System.out.println("completable-subscribed");
    }
};

completable
        .andThen(observable)
        .subscribe(integer -> System.out.println("emitted:"+integer));

And this is my output:

completable-subscribed

The observable is not even being subscribed. What am I doing wrong?

[akarnokd]

For one, you implemented Completable incorrectly and in a way most people don't need to do it. Use Completable.create() instead. Second, you have to complete the CompletableObserver, otherwise andThen won't know to switch to the other source.

Completable completable = Completable.create(emitter -> {
    emitter.onComplete();
});

completable
        .andThen(observable)
        .subscribe(integer -> System.out.println("emitted:"+integer));

[amanshuraikwar]

@akarnokd It works now, I was not completing the Completable. Thanks for your help! I really appreciate it.

[AlexeyPoldeo]

This is definitely frustrating issue for beginners. I think it's good idea to do something to warn on incorrect usage.

[ursusursus]

This is a very silly api tbh, everyone I know was burned by this