Is it possible to start observation when launching...

# coroutines

[Daniel Rodak]

Is it possible to start observation when launching StateFlow? So the case is that I have StateFlow in my ViewModel and I would like to launch some observation(e.g. User status Flow) but I would like to stop this observation at the same moment that I will stop observing main StateFlow itself so they need to be launched in the same scope. Currently I’m using combine with status observation flow but I’m ignoring events emitted by this Flow, is there a better way to handle it? Side not: I'm not using values emitted by the second flow directly so that's why I need to ignore them.

[Stylianos Gakis]

val stateFlow: StateFlow<T> = flow {
  userStatusFlow.collect {
    emit(it)
  }
}
.stateIn(
  null or whatever initial value,
  WhileSubscribed(5.seconds),
  viewModelScope,
)

This will keep the userStatusFlow alive as long as there is someone subscribed to this flow (and 5 seconds after that).
Is this what you’re going after?
If you throw in some more code it might be easier to map it to your use case

[Daniel Rodak]

Thanks for suggestion! Unfortunately it’s not exactly what I’m trying to achieve but I will share some code. I have ViewModel which contains private MutableStateFlow and public Flow on which I’m collecting with lifecycle scope in my Fragment. And that’s important that I’m not using viewModelScope here. The code in view model looks like this:

private val state = MutableStateFlow<SomeState>(SomeState())
    val viewState: Flow<SomeViewState> = state
        .combineWithSideEffectFlow(observeSomeData()) // <- this is the part I'm trying to make simpler
        .map(mapper::from) // <- ignore this, just mapping
...
		private fun observeSomeData(): Flow<SomeData> {
				... 
				state.emit(...)
		}

And combineWithSideEffectFlow function is complicated at this moment because it uses combine to subscribe on the second flow using same scope as the main flow so the one from the Fragment. I’m ignoring events emitted by this observation observeSomeData. So what I’m trying to achieve would be something like current .onSubscription method but with the same scope as the StateFlow on which it will be called.

val viewState: Flow<ProductDetailsViewState> = state
        .collectAlso(observeDraftOrder())
        .map(mapper::from)

[Rick Clephas]

Can't you use combine directly?:

val viewState: Flow<SomeViewState> = state.combine(observeSomeData()) { state, _ -> state }.map(mapper::from)