Hi, I can't find how to remove a subscriber to a StateFlow since collect never terminates. I just w...

# coroutines

[Justin Tullgren]

Hi, I can't find how to remove a subscriber to a StateFlow since collect never terminates. I just want to stop listening once a certain state is emitted. Thanks

scope.launch { stateFlow.collect { if (it is State) doWork(); /* how do i unsubscribe here? */ } }

[Joffrey]

This should do:

scope.launch {
    stateFlow.takeWhile { it is State }.collect { doWork() }
}

[Justin Tullgren]

okay I thought I tried that and transformWhile but i'll double check. I might have been blocking something and it never completed.

[Justin Tullgren]

i'll get back to you thanks!

[Nick Allen]

You may also be looking for something like:

scope.launch {
    val item = stateFlow.first() //wait for first item
    if (item is State) {
        doWork()
    }
}

Not really sure if the code snippet you wrote is exactly what you meant. I read that as "check the first item if work should be done and then stop listening regardless of what it is."

[Joffrey]

Ah yeah I sort of assumed an else there, but technically you're right @Nick Allen

[Justin Tullgren]

I'm looking to listen until a state is emitted and then stop listening

[Justin Tullgren]

so any number of emissions can be ignored until the correct state is emitted

[Justin Tullgren]

so the takeWhile is what i was expecting but it never completed in my sample

[Joffrey]

Then I don't believe takeWhile is what you want here. If you want to subscribe and wait for the first item that is a State you should use val state = stateFlow.first { it is State } . Or if you want to avoid casting to State you could use:

scope.launch {
    val item = stateFlow.filterIsInstance<State>().first()
    doWork()
}

[Justin Tullgren]

ok i'll give it a whorl! thanks

[Justin Tullgren]

that worked thank you!