Destination results

Khonshu has a built-in way to receive results from another screen inside the app. For that it is required to call HostNavigator.registerForNavigationResult<Route, Result>. Route in this case should be the NavRoute class for the current screen, while Result is the type of the expected result which can be any Parcelable class. The register method will return a NavigationResultRequest, which has a results property that returns a Flow<Result> to collect the results.

The navigation to the screen from which the result should be returned is a regular call to navigateTo. However the NavRoute class for that target destination should have NavigationResultRequest.Key<Result> as a parameter. An instance of such a Key can be obtained from the key property of the request object.

The target screen can then simply call deliverNavigationResult(route.key, result) on its own navigator to send the result and afterwards remove itself from the back stack with navigateBack.

The logic for a hypothetical FooScreen that wants to receive a result from BarScreen would look like this:

data class MessageResult(val message: String): Parcelable

class FooScreenViewModel(
    private val hostNavigator: HostNavigator
) {
    // use request.results somewhere to handle the results that BarScreen delivers
    val request = hostNavigator.registerForNavigationResult<FooScreenRoute, MessageResult>()

    fun navigateToScreenB() {
        // if needed BarScreenRoute could also have additional parameters
        hostNavigator.navigateTo(BarScreenRoute(request.key))
    }
}

BarScreen would then have the following route and logic:

data class BarScreenRoute(
    val key: NavigationResultRequest.Key<MessageResult>,
) : NavRoute

class BarScreenViewModel(
    private val hostNavigator: HostNavigator,
    val route: BarScreenRoute,
) {
    fun deliverMessage(message: String) {
        hostNavigator.deliverNavigationResult(route.key, MessageResult(message))
    }
}