Generating the Activity

Similar to generating the set up for each screen, Khonshu also supports generating an Activity and the set up that is required for it. To do that add the @NavHostActivity annotation to a @Composable function. The composable will then be shown in the generated Activity.

 // a scope marker used to represent the `Activity`.
sealed interface ExampleActivityScope

@NavHostActivity(
    scope = ExampleActivityScope::class,
    parentScope = AppScope::class, // AppScope is the default value and can be omitted
    stateMachine = ExampleStateMachine::class,
    activityBaseClass = ComponentActivity::class, // the super class for the generated activity
)
@Composable
internal fun ExampleUi(
  state: ExampleState,
  sendAction: (ExampleAction) -> Unit,
  navHost: SimpleNavHost,
) {
    // place the given NavHost composable
    navHost(Modifier.fillMaxSize()) { root, route -> /* route changed listener */ }
}

The scope and parentScope work the same as route and parentScope for the destination code generation. stateMachine also behaves the same and the composable will receive state from it and can use sendAction to talk to the state machine.

A new parameter is the navHost composable. This composable is a pre-configured NavHost that already has all destinations and deep links added to it. This leaves 2 parameters when calling the composable: - A Modifier to influence how the NavHost is shown on screen - A (NavRoot, BaseRoute) -> Unit) function that will be called whenever the currently shown destination changes. This is optional and null can be passed instead.

The code generation will automatically take care of creating a HostNavigator and makes it available in the scope. This means any screen can simply inject HostNavigator to use it.

One requirement is that the destinationScope used by other screens is either the scope or parentScope (or a parent of the parent if there are deeper scope hierarchies) used for @NavHostActivity. Otherwise the Set<NavDestination> won’t be available for injection and Metro will fail when injecting dependencies.