Hi, I’m trying to migrate to the new compose versi...

# compose

[nglauber]

Hi, I’m trying to migrate to the new compose version and facing this issue:

Flow operator functions should not be invoked within composition

Basically, almost all flows of my app are using something like this:

val someStateInViewModel by viewModel.myState.flowInLifecycle()
    .collectAsState(initial = null)

This flowInLifecycle function is doing the following:

@Composable
fun <T> Flow<T>.flowInLifecycle(): Flow<T> {
    val lifecycleOwner = LocalLifecycleOwner.current
    return remember(this, lifecycleOwner) {
        this.flowWithLifecycle(lifecycleOwner.lifecycle, Lifecycle.State.STARTED)
    }
}

Any suggestion? Because I’m using this function is 225 places in my app 😭

[Will Shelor]

why do you nee flowInLifecycle? My understanding is that coroutines should be able to handle their own subscriptions/unsubscriptions in their state. Does something go wrong if it’s removed?

[nglauber]

I did this implementation based on this article by @Manuel Vivo
https://medium.com/androiddevelopers/a-safer-way-to-collect-flows-from-android-uis-23080b1f8bda

Even if Compose doesn’t recompose the UI when the host activity or fragment is in the background, the flow producer is still active and can waste resources. Compose can suffer from the same problem as the View system.

When collecting flows in Compose, use the Flow.flowWithLifecycle operator as follows:

[tad]

The reason the warning pops up is to prevent the accidental creation of new Flow objects on every recomposition. Your operator doesn't do that (it uses remember under the hood), but it also doesn't do anything collectAsState doesn't already do, as the coroutine scope it uses doesn't outlive LifecycleScope.

If you're using StateFlow then no other operator is required to keep it hot for multiple collectors, but if you want to avoid creating a hot flow for each collector, use shareIn(viewModelScope) with the appropriate restart policy in the ViewModel.

[nglauber]

thanks for the clarification @tad, I’m using StateFlow in my viewmodel, so I think I’m good 🙂

[Adam Powell]

Might be worth filing feedback for the lint warning, if you declare a flow operator as @Composable we could assume you know what you're doing w.r.t. avoiding recomposition causing a cancel/re-collect for a new Flow instance