LaunchedEffect not restarted after backgrounding Circuit app

[itsandreramon]

Moved this into discussions as requested:

I ran into an edge-case lately that involves backgrounding and foregrounding a Circuit app I've been developing. Basically what happens is that I have a Presenter that uses LaunchedEffect (or in our case RememberedEffect which is the same as LaunchedEffect but without a coroutine attached) to start Interactors. In our case we have a SubjectInteractor which allows me to observe a list of items from local storage. To avoid restarting in compositions we internally use a ParamStateFlow with distinctUntilChanged similar to what Tivi is using. Although I don't think it has to do with the issue I will just leave the code here:

abstract class SubjectInteractor<P, R> {

  private val paramState =
    MutableSharedFlow<P>(
      replay = 1,
      extraBufferCapacity = 1,
      onBufferOverflow = BufferOverflow.DROP_OLDEST,
    )

  val observable: Flow<R> =
    paramState
      .distinctUntilChanged()
      .flatMapLatest { params -> createObservable(params) }
      .distinctUntilChanged()

  operator fun invoke(params: P) {
    paramState.tryEmit(params)
  }

  protected abstract fun createObservable(params: P): Flow<R>
}

@Inject
class ObserveTasks(
  private val taskRepository: TaskRepository
) : SubjectInteractor<Unit, Resource<List<Task>>>() {
  override fun createObservable(params: Unit): Flow<Resource<List<Task>>> {
    return taskRepository.observeTasks()
  }
}

The presenter injects them like this:

@Inject
@CircuitInject(SelectTaskScreen::class, UiScope::class)
class SelectTaskPresenter(private val observeTasks: ObserveTasks) : Presenter<SelectTaskUiState> {

  @Composable
  override fun present(): SelectTaskUiState {
    val tasksResource by observeTasks.observable.collectAsRetainedResource()
    LaunchedEffect(Unit) { observeTasks(Unit) }
    return SelectTaskUiState(...)
}

So when entering the screen, the LaunchedEffect kicks off the SubjectInteractor and we get updates that we can show in Ui. Backgrounding the app and foregrounding again causes the LaunchedEffect to not restart with Unit as a key. This causes the tasksResource to not be updated. The presenter is recreated (e.g. new UiComponent etc.) and our App composable is restarted properly. We could fix this issue by just passing hashCode of the Presenter class as key but this feels like a workaround.

[stagg]

The LaunchedEffect itself will be launched if the composition is started, which it sounds like it is. Should be able to drop a breakpoint in it and see that.

It's a little hard to know what could be wrong without knowing what collectAsRetainedResource() or what taskRepository.observeTasks() does. For example, the SubjectInteractor with a P parameter of Unit will only ever call createObservable() once so if there's any initialization there thats needed it won't run again. Or if collectAsRetainedResource is capturing a coroutine scope from the composition, then that would have been canceled.