Hello, is there any best practice to return a `State<T>` AND a `StateFlow<T>` , backed b...

# compose

[Steffen Funke]

Hello, is there any best practice to return a State<T> AND a StateFlow<T> , backed by the same changing data, at the same time from an Android ViewModel? I have some View based UI which consumes the data as StateFlow, and some Compose UI, which would need State. And ideally I don’t want to rewrite the Compose part to collectAsState(), rather just have it consume State directly from ViewModel (e.g. hide the implementation details inside ViewModel):

Inside ViewModel:
    // is consumed by View based UI
    protected val _itemsFlow = MutableStateFlow<List<Item>>(emptyList())
    val itemsFlow = _itemsFlow.asStateFlow()

    // should be consumed by Compose UI
    val items: State<List<Item>> = itemsFlow.collectAsState() // not working bc. of missing @Composable scope
    val items: State<List<Item>> = itemsFlow.collectAsState(emptyList()) // also not working

[Zoltan Demant]

You could use State<T> over StateFlow<T> in your ViewModel, if thats a viable option for you?

[Steffen Funke]

Hm, mind you have an example how to use mutableStateOf(List<T>) inside VM, and get an StateFlow<List<T>> out of it 🤔 ?

[Zoltan Demant]

I meant completely replacing StateFlow with State, heres a relevant discussion!

[Steffen Funke]

I know I can use State inside viewModel, but my old View part would need this data then as StateFlow… how to do the exposing from State to StateFlow, if I am using State inside VM (which I would prefer as well)? Sorry I think I have some blockage at the moment …

[Steffen Funke]

Might SnapshotFlow be a way to convert mutablestate to StateFlow? Have to read about it.

[Steffen Funke]

Hm, am I on the right track here? At least the data types are fine now 🙂 But is itemsFlow updating, when items are?

// Inside VM
var items by mutableStateOf(emptyList<Item>())
        protected set
    
val itemsFlow = snapshotFlow { items }

[Zoltan Demant]

I dont know if this is a good idea:

class StateExample<State>(initial: State) {

    private val state = MutableStateFlow(initial)

    val composableState
        @Composable
        get() = state.collectAsState()
}

@Composable
fun Test(example: StateExample<String>) {
    val state by example.composableState
    
    state // <- String!
}

[Steffen Funke]

Thanks all, snapshotFlow was the missing piece to convert a mutableStateOf into StateFlow<T> , see above. Working now! 🥳

[Jaime]

@Steffen Funke If I understood correctly, this can help you https://developer.android.com/reference/kotlin/androidx/compose/runtime/package-summary#producestate