Subscribe after collect doesn't work

Question

I'm experimenting with RxJava. I need an Observable , which produces a HashSet<String> . Into Observable I want to be abele to put Pair<String, Boolean> in the way that false boolean value removes the String key from the resulting HashSet . Here's a code snippet of what I have:

private val selectionSubject = ReplaySubject.create<Pair<String, Boolean>>()
init {
    selectionSubject.onNext(Pair("dd", false))
    selectionSubject
        .collect({HashSet<String>()}, {dest, value -> collectSelection(dest, value)})
        .subscribe { t1, t2 -> Log.d(TAG, t1.toString())}
}

private fun collectSelection(dest: HashSet<String>, value: Pair<String, Boolean>): HashSet<String> {
    if (value.second) {
        dest.add(value.first)
    } else {
        dest.remove(value.first)
    }
    Log.d(TAG, "collectSelection, ${dest.toString()}")
    return dest
}

In the logs I can see that collectSelection gets called but my subscribe listener doesn't.

How can it be fixed?

Answer 1

collect waits for onComplete event from the stream above before emitting a value. In your case, ReplaySubject never ends and thus no value is emitted.

Without knowing the context of selectionSubject I can't provide a solution to your problem, like, does it have to remain open? If there are limited onNext calls, you can use .take(X) . If it has to remain open, you shouldn't depend on collect but add the item inside on HashSet in something like .doOnNext