Is there a way to use `collectAsState ` or an equivalent ins kotlinlang #compose

08/30/2021, 9:59 AM

Is there a way to use

collectAsState()

(or an equivalent) inside of a

LazyListScope

(outside of a

@Composable

)? The usecase is conditionally emitting either A or B items, depending on the content of a

StateFlow

Would this work? 🤔

val x = derivedStateOf {
  controllingStateFlow.value
}

Felix Schütz

08/30/2021, 10:51 AM

Is there one

StateFlow

for each item?

08/30/2021, 10:57 AM

No, there is a stateflow which basically holds a yes/no decision, depending on that flow the form should emit items contained in another stateflow

Felix Schütz

08/30/2021, 11:03 AM

But you can't decide between items A and B outside of the

LazyColumn

LazyRow

08/30/2021, 2:30 PM

There is no UI workaround that I can think of.. But I tried mapping the StateFlow inside of the ViewModel like so:

fun <T> StateFlow<T>.asComposeState(scope: CoroutineScope): State<T> {
    val outState = mutableStateOf(value)
    scope.launch {
        collect {
            outState.value = it
        }
    }
    return outState
}

~~It semy works, not sure why but the first emission is swallowed~~

Actually it works brilliantly, I had an error somewhere else in my rendering code 🙂

Zach Klippenstein (he/him) [MOD]

08/30/2021, 4:49 PM

I don’t understand why you don’t want to use

collectAsState

though, because this should work:

val decision by decisionFlow.collectAsState()

LazyColumn {
  if (decision) {
    items(…)
  } else {
    items(…)
  }
}

08/30/2021, 7:39 PM

I need to collect the state inside of a reused section inside of the LazyColumn, e.g.

@Composable
fun Parent() {
  LazyColumn {
    DecisionSection(viewModel.decisionForm)
  }
}

fun LazyListScope.DecisionSection(decisionForm: DecisionForm){
  val decision by decisionForm.decision.collectAsState() <-- Can't do, because this is not inside of a composable
  if (decision) {
    items(…)
  } else {
    items(…)
  }
}

DecisionSection

might be 3 layers down the hierarchy as the above example is extremely simplified. I could hoist

decision

but then I would need to pass about 20 parameters from the top level down, which is very cumbersome for lots of reasons.