Let's say you have some logic in your ViewModel that should trigger a snackbar in your UI/Composable. How do you send that event? In XML times I used an event channel but this doesn't seem to work well with Compose since 2 times the same snackbar text in a row gets ignored by the

mutableStateOf

holder.

I've had this question and conversation way more times on this channel than I care to admit. And probably like 2-4 times in the past ~3 week. If you want to look through adam powells history on slack you can probably find some good conversations that way, but I also asked for more documentation and guidance surrounding this here if you want to star. https://issuetracker.google.com/issues/194911952

Thanks. Yea I read one of those threads but it was quite messy to read through

Yeah. Messy and informative, but to the pragmatic person of "Hi. I'm a long time developer and now I am using compose. How do I do this?" it's not really reasonable. After all of those conversations I still don't really have a good answer. I suppose I have three approaches: 1. I try to make things state when I can, and following off of that, I just have been acknowleding that a snackbar was shown for example (just by resetting the state) 2. I use state to launch a LaunchedEffect or DisposableEffect (@zhuinden showed me some stuff around that here https://github.com/ColtonIdle/ComposeSignInSample/pull/1) 3. For navigation events, I basically call a viewmodel.doNetworkCall(success = mySuccessEvent, failure = myFailureEvent)

I’ve come across this article: https://codingtroops.com/android/compose-architecture-part-1-mvvm-or-mvi-architecture-with-flow/?s=09 haven’t tried but definitely going to :)

thanks, I'll look through that stuff in a bit!

Nothing. Except for the fact that it seemed like I needed a phd to understand anything related to flows and channels and such. I just need something that works. Emitting state, and then acking that a snackbar was shown was much easier, less error prone, and made sense to my teammates too. /shrug

and how do you reset that state so the snackbar is not shown again on screen rotation?

I just have something like If (state.showSnackBar){ showIt() State.showSnackBar = false } It's... Primitive. Maybe not the best. But it works.

yea it's an option

I'm using Channel to show snackbar, refresh indicators, and such just like from the article Alexey shared (I'm actually following the exact pattern from the article) and I face no issue in that. What problem do you face by using Channel?

I also used to use channels in XML times

ok, for this specific case, I'm not transforming the

Channel

into

mutableStateOf

. Like from the article, I expose the Channel as

Flow

to the composable. And in the composable, I use

LaunchedEffect(Unit)

to collect the flow and respond to that. This way I can consume all events emitted to the channel since the flow actually suspends until my task from

onEach/collect

is completed before emitting next item. Roughly like this,

fun MyComposable(effectFlow: Flow<Effects>){
  LaunchedEffect(Unit){
    effectFlow.onEach{
        //do thing with it
    }.launchIn(this)
  }
}

At that point, couldn't you just use state and based on the state you just have a LaunchedEffect?

In this way, I can queue the event handling. If a snackbar message is emitted while another one is showing, the new one will be handled only after the previous task is finished since the flow operators are suspend functions.

@muthuraj but what do you do with the snackbar text you receive through the channel? You have to get it into the snackbar somehow.

In the collect block, I show the snackbar directly using

scaffoldState.snackbarHostState.showSnackbar

.

yea I guess that makes more sense

yeah

now that I look at it again, the snackbarMessage MutableState doesn't make sense anyway

My case is actually simpler. I use the

Scafflold

in the same function that I handle these events. But passing

scaffoldState

or even just

snackbarHostState

should work I think.

thank you

You can use

collectLatest

instead of

collect.

@muthuraj you're a genius

@Florian looking forward to the video/blog post. Make this easy for me please. 🙏

So the TL;DR is something like this?

sealed class Effect {
    // different effects ...
}

class ViewModel {
    private val _effect = Channel<Effect>()
    val effect: Flow<Effect> = _effect.receiveAsFlow()
}

@Composable
fun Screen(viewModel: ViewModel) {
    LaunchedEffect(Unit) {
        viewModel.effect.collect { effect ->
            when (effect) {
                // handle cases ...
            }
        }
    }
}

Right. This is also what I did in XML times (minus the LaunchedEffect of course)