Events — Android

Events are one-shot messages sent from a ViewModel to a Composable. They are backed by a Channel, which guarantees single delivery even during screen rotation.

Defining Events

Define events as a sealed class extending Event<VS>:

sealed class HomeEvent : Event<HomeViewState>() {
    object ShowDetailEvent : HomeEvent()
    data class ShowMessageEvent(val message: String) : HomeEvent()
}

Sending Events

Send an event from the ViewModel:

sendEvent(ShowDetailEvent)

Collecting Events in Compose

Use EventsEffect to collect events in a Composable:

@Composable
fun HomeScreen(viewModel: HomeViewModel = hiltViewModel()) {
    viewModel.EventsEffect {
        onEvent<ShowDetailEvent> { /* navigate to detail */ }
        onEvent<ShowMessageEvent> { showSnackbar(it.message) }
    }
}

EventsEffect is an extension function on BaseCoreViewModel from the compose module. It launches a coroutine that collects events for the lifetime of the Composable.

onEvent<E> is a type-safe filter — it checks whether the received event is of type E and executes the lambda only when it matches.