How to show snackbar with a button onclick in Jetpack Compose

You'll need two things:

1. SnackbarHostState - which will manage the state of your Snackbar (you would usually get that from the ScaffoldState)
2. CoroutineScope - which will be responsible for showing your Snackbar

@Composable
fun SnackbarDemo() {
  val scaffoldState = rememberScaffoldState() // this contains the `SnackbarHostState`
  val coroutineScope = rememberCoroutineScope()

  Scaffold(
        modifier = Modifier,
        scaffoldState = scaffoldState // attaching `scaffoldState` to the `Scaffold`
    ) {
        Button(
            onClick = {
                coroutineScope.launch { // using the `coroutineScope` to `launch` showing the snackbar
                    // taking the `snackbarHostState` from the attached `scaffoldState`
                    val snackbarResult = scaffoldState.snackbarHostState.showSnackbar(
                        message = "This is your message",
                        actionLabel = "Do something."
                    )
                    when (snackbarResult) {
                        Dismissed -> Log.d("SnackbarDemo", "Dismissed")
                        ActionPerformed -> Log.d("SnackbarDemo", "Snackbar's button clicked")
                    }
                }
            }
        ) {
            Text(text = "A button that shows a Snackbar")
        }
    }
}

You can use this

@Composable
fun MainScreen() {
    val coroutineScope = rememberCoroutineScope()
    val showSnackBar: (
        message: String?,
        actionLabel: String,
        actionPerformed: () -> Unit,
        dismissed: () -> Unit
    ) -> Unit = { message, actionLabel, actionPerformed, dismissed ->
        coroutineScope.launch {
            val snackBarResult = scaffoldState.snackbarHostState.showSnackbar(
                message = message.toString(),
                actionLabel = actionLabel
            )
            when (snackBarResult) {
                SnackbarResult.ActionPerformed -> actionPerformed.invoke()
                SnackbarResult.Dismissed -> dismissed.invoke()
            }
        }
    }


    showSnackBar.invoke(
        "YOUR_MESSAGE",
        "ACTION_LABEL",
        {
         //TODO ON ACTION PERFORMED
        },
        {
         //TODO ON DISMISSED
        }
    )
}

Building on Bartek's answer you can also use Compose's side-effects. Then you don't have to manage the CoroutineScope itself.

Since Composables itself should be side-effect free, it is recommended to make use of Compose's Effect APIs so that those side effects are executed in a predictable manner.

In your specific case you can use the LaunchedEffect API to run suspend functions in the scope of a composable. The example code would look like the following:

@Composable
fun SnackbarDemo() {
    val scaffoldState = rememberScaffoldState() // this contains the `SnackbarHostState`
    val (showSnackBar, setShowSnackBar) = remember {
        mutableStateOf(false)
    }
    if (showSnackBar) {
        LaunchedEffect(scaffoldState.snackbarHostState) {
            // Show snackbar using a coroutine, when the coroutine is cancelled the
            // snackbar will automatically dismiss. This coroutine will cancel whenever
            // `showSnackBar` is false, and only start when `showSnackBar` is true
            // (due to the above if-check), or if `scaffoldState.snackbarHostState` changes.
            val result = scaffoldState.snackbarHostState.showSnackbar(
                message = "Error message",
                actionLabel = "Retry message"
            )
            when (result) {
                SnackbarResult.Dismissed -> {
                    setShowSnackBar(false)
                }
                SnackbarResult.ActionPerformed -> {
                    setShowSnackBar(false)
                    // perform action here
                }
            }
        }
    }
    Scaffold(
        modifier = Modifier,
        scaffoldState = scaffoldState // attaching `scaffoldState` to the `Scaffold`
    ) {
        Button(
            onClick = {
                setShowSnackBar(true)
            }
        ) {
            Text(text = "A button that shows a Snackbar")
        }
    }
}

If you use new Material3 there is new field in Scaffold: "snackbarHost"

val snackbarHostState = remember { SnackbarHostState() }
val scope = rememberCoroutineScope()

Scaffold(
  snackbarHost = { SnackbarHost(snackbarHostState) },
  ...

            // for showing snackbar in onClick for example:
            scope.launch {
                snackbarHostState.showSnackbar(
                    "Snackbar Test"
                )
            }

Let me add an other answer, i was not using scaffold and was using state hoisting

val loginState by viewModel.uiState.collectAsState() // STATE HOISTING
val snackbarHostState = remember { SnackbarHostState() }
val message = stringResource(id = R.string.error_login) 
if (loginState.snackbarVisible) { // When passing true, show snackbar
    LaunchedEffect(snackbarHostState) {
        snackbarHostState.showSnackbar(
            message = message,
            actionLabel = "Do something."
        )
    }
}


Box(
    modifier = Modifier.fillMaxSize()
) {
    // Your screen content
    // ...
    SnackbarHost(
        hostState = snackbarHostState,
        modifier = Modifier.align(Alignment.BottomCenter)
    ) // Snackbar location
}

First of all you need a SnackbarHostState, you can pass this state down to your composable where you want to trigger a snackbar message. or if you use a scaffold use that one scaffoldState.snackbarHostState

val snackbarHostState = remember { SnackbarHostState() }

Showing a snackbar is a side effect and should be wrapped in a LaunchEffect Composable

@Composable
fun MyScreen(
    scaffoldState: ScaffoldState = rememberScaffoldState()
) {
   Scaffold(scaffoldState = scaffoldState) {    

     Button(onClick = {
      LaunchedEffect(scaffoldState.snackbarHostState) {
         scaffoldState.snackbarHostState.showSnackbar(
                  message = "hello world",
                  actionLabel = "Retry"
         )
      }

    
     // ...
    }
}

See more information here https://developer.android.com/topic/architecture/ui-layer/events#consuming-trigger-updates

and https://developer.android.com/jetpack/compose/side-effects

You can show snackBar without Scaffold using SnackBar Composable either.

Box(modifier = Modifier.fillMaxSize()) {
    var showSnackbar by remember {
        mutableStateOf(false)
    }

    LaunchedEffect(key1 = showSnackbar) {
        if (showSnackbar) {
            delay(2000)
            showSnackbar = false
        }
    }


    Column {

        Button(onClick = {
            showSnackbar = !showSnackbar
        }) {
            Text("Show Snackbar")
        }
    }

    if (showSnackbar) {
        androidx.compose.material.Snackbar(modifier = Modifier.align(Alignment.BottomStart),
            action = {
                Text(text = "Action",
                    color = Color(0xffCE93D8),
                    modifier = Modifier.clickable {
                        showSnackbar = false
                    }
                )
            }) {
            androidx.compose.material.Text("Message")
        }
    }
}

LaunchedEffect is to remove it from composition. You can use a slide animation if you want to.