How to show snackbar in Jetpack Compose material 3

Question

I started to learn Jetpack Compose and it looks confusing how to implement a simple snackbar, using material3 dependencies.

Documentation shows I need a scaffold and it needs a content with padding (?). Do I need put my screen composable inside scaffolds lambda? How do I pass my message text to Snackbar? I have a simple flow collector for event from viewmodel where I want to pass the error text to snackbar.

Test()
LaunchedEffect(Unit) {
    viewModel.loginEvent.collect {
        when (it) {
            is LoginViewModel.LoginEvent.Error -> {
             // show snackbar with it.error
            }
       
            is LoginViewModel.LoginEvent.Success -> {
              // 
            }
        }
    }
}

@Composable
fun Test() {
    Box(modifier = Modifier.fillMaxSize()) {
//my composable screen
}

Answer 1

You can use a scaffoldHostState to show a snackbar inside a scaffold and yes, you should use the scaffoldPadding for the padding of e.g. a topAppBar, navigationBar ...

Can you try this?

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun Screen() {
    val snackbarHostState = remember { SnackbarHostState() }

    val localCoroutineScope = rememberCoroutineScope()

    LaunchedEffect(Unit) {
        viewModel.loginEvent.collect {
            when (it) {
                is LoginViewModel.LoginEvent.Error -> {
                    // show snackbar with it.error
                    localCoroutineScope.launch {
                        snackbarHostState.showSnackbar(
                            message = "Error message"
                        )
                    }
                }
                // ...
            }
        }
    }

    Scaffold(
        snackbarHost = { SnackbarHost(snackbarHostState) }
    ) { scaffoldPadding ->
        Box(
            modifier = Modifier
                .padding(scaffoldPadding)
                .fillMaxSize()
        ) {
            // your composables ...
        }
    }
}