RxJava2从侦听器创建Flowable并在最后删除侦听器

Question

My use case is related to using RxJava2 with Firebase Database.

I have a DatabaseReference and I can register value listeners to it. I can transform it into a flowable like this:

disposable = Flowable.create<DataSnapshot>({ s ->
            dbRef.addValueEventListener(object : ValueEventListener {
                override fun onCancelled(p0: DatabaseError) {...}

                override fun onDataChange(value: DataSnapshot) {
                    s.onNext(value)
                }
            })
        }, BackpressureStrategy.BUFFER)
        .subscribe(...)

I would like to be able to remove the listener when the disposable is disposed. Any idea how I can do that?

I saw that in rxjava 1 there was this possibility maybe, but it's not available in rxjava2

Answer 1

With RxJava2 you need to use the setCancellable() method, and put your listener removal code there.
This is much like Emitter.setCancellation() from RxJava1, when creating Observable with Observable.fromEmitter() .

Take also this note by akarnokd regarding cancellation:
"But note that unless the create logic gives up the scheduler (by terminating or going async), the cancellation logic may not ever execute due to same-pool livelock." ( RxJava 2: always unsubscribe on the .subscribeOn(..) scheduler? )