What’s the best practice for triggering snackbars (outside onClick)?

LaunchedEffect(error) {
  snackbarState.showSnackbar(error.message)
}

I have this but this doesn’t run if exactly the same error happens.

IMO you could include a unique identifier in your

Error

Maybe you should take a look here: https://developer.android.com/reference/kotlin/androidx/compose/material/package-summary#SnackbarHost(androidx.compos[…]odifier,%20kotlin.Function1)

Thanks. The sample is too simple, it just shows a snackbar immediately on click.

As long as you have access to scafoldState you can trigger the snackbar whenever you want.

I can trigger it whenever, but it’s not triggering when want it to for some cases😄

Before this SnackbarHost existed i implemented (and still using) my own custom implementation:

class SnackbarController() {
    internal val snackbarList = mutableStateListOf<@Composable SnackbarScope.() -> Unit>()
    fun showSnackbar(snackbar: @Composable SnackbarScope.() -> Unit) {
        snackbarList.add(0, snackbar)
    }
    fun removeSnackbar(snackbar: @Composable SnackbarScope.() -> Unit) {
        snackbarList.remove(snackbar)
    }
}

@Composable
fun SnackbarContainer(modifier: Modifier = Modifier, snackbarController: SnackbarController) {
    val list = snackbarController.snackbarList
    list.firstOrNull()?.let { snackbar ->
        val scope = remember(snackbar) { SnackbarScope(snackbarController, snackbar) }
        Box(modifier) {
            snackbar(scope)
        }
    }
}
class SnackbarScope(private val snackbarController: SnackbarController, private val snackbar: @Composable SnackbarScope.() -> Unit) {
    fun dismiss() {
        snackbarController.removeSnackbar(snackbar)
    }
}

I have this but this doesn’t run if exactly the same error happens.

^ this is the use case I need to handle

I will try to hack a minimal sample into a open repo so you can see how it is working.

don't do this in a

@Composable

function:

val job = scope.launch {

we should probably have a lint error for any use of

CoroutineScope.launch

or

CoroutineScope.async

inside of a composable function. You want

LaunchedEffect

instead.

Hi Adam! 🙂 Any idea here? This issue just started to happen from alpha08 (at least) actually, it seems new optimization code got in and now checks for equality to avoid recomposition.

For the original question? Yes, that's what I would expect 🙂 can you show the code where the error originates and how it gets to the snippet in the OP?

Tried to write a minimal sample. I hope this helps illustrate the problem and what I expect

@Adam Powell yessss. need more lint warnings/errors. I feel like it's going to be critical to get people going in the right direction during the early adoption phase.

Busy for a little while longer here but I'll come back to this later

@Adam Powell but how can i than cancel the coroutine? LaunchedEffect do not return a reference to the job

@Timo Drick it doesn't have to, the job is maintained by the composition. If one of the other parameters changes, the old job will be cancelled and a new one launched. If the

LaunchedEffect

leaves the composition entirely, the job will be cancelled.

Yes i know. But in my usecase i want to cancel the job before the compose is changed because otherwise the onDismiss() is called.

you've got a bigger problem of identity though; remember, that function can be recomposed at any time for any reason, and you're launching that delay+dismiss every time

Ok yes. That is a good point. I think i understand the problem now.

Compose likes to work in terms of stable state. Error displays come in different flavors depending on what originated them. The idea of a "current" error is state; if you're displaying an error with a timeout, launch the timeout with a subject/key parameter of the current error. If you press a button to acknowledge the error, clear the current error - it will naturally cancel the timeout.

That makes sense! I think I see what you mean. I think this should work, or is there a better way to do this?

Looks good to me 👍

Thanks Adam! This is really great info.