Side Effects & Lifecycle

Why side effects need care

Composables can run many times (recomposition). To run something once or in response to a key change, use effect APIs instead of calling it directly in the body.

LaunchedEffect

@Composable
fun Profile(userId: Int, vm: ProfileViewModel) {
    LaunchedEffect(userId) {
        vm.load(userId)     // runs when userId changes
    }
}

rememberCoroutineScope (event-driven)

val scope = rememberCoroutineScope()
Button(onClick = {
    scope.launch { snackbarHostState.showSnackbar("Saved!") }
}) { Text("Save") }

Collecting state from a ViewModel

val uiState by viewModel.state.collectAsStateWithLifecycle()

Rule: never start coroutines or network calls directly in a composable body — wrap them in LaunchedEffect or an event handler.