What’s the proper way to show an one time even? Fo...

# compose

[Tgo1014]

What’s the proper way to show an one time even? For example a toast from a SharedFlow ?

[Csaba Kozák]

You should use a side-effect composable for that. LaunchedEffect is perfect for this. See this example.

[Tgo1014]

My concern is the “collecting” part. So I should make an if to see if the flow has some value and then launch the toast? I see the scaffold have some snaback state, but what about something else that doesn’t have this state ready for you?

[Csaba Kozák]

You can add a SnackbarHost() outside of a Scaffold as well.

[Damian Zawadzki]

you can pass any key you want to launched effect, but not sure how null key for instance would work with recompositions. I got one snippet for vm in mvi architecture that collects effects in compose:

LaunchedEffect(key1 = "PackagesStartFormEffects") {
                viewModel.effect.collect { effect ->
                    val message = when (effect) {
                        PackagesStartFormContract.Effect.FormConfirmed -> {
                            "Form confirmed!"
                        }
                        is PackagesStartFormContract.Effect.UnknownError -> {
                            effect.message ?: "Unknown error."
                        }
                    }
                    snackbarHostState.showSnackbar(
                        message = message,
                        actionLabel = label,
                        duration = SnackbarDuration.Long
                    )
                }
            }

but it feels like ""PackagesStartFormEffects" is not elegant solution to fulfill the key1 parameter requirement. I think that passing null would do same thing.

[Damian Zawadzki]

I've found some other example of key parameter by searching for @Csaba Kozák suggestion here:
https://developer.android.com/reference/kotlin/androidx/compose/material/SnackbarHostState

[Damian Zawadzki]

val channel = remember { Channel<Int>(Channel.Factory.CONFLATED) }
LaunchedEffect(channel) {
    channel.receiveAsFlow().collect { index ->
        val result = snackbarHostState.showSnackbar(
            message = "Snackbar # $index",
            actionLabel = "Action on $index"
        )

here is channel as parameter.

[Tgo1014]

I guess in this last document I found what as was doing wrong. Instead of collectAsState() the example just collect{} and do what’s needed