IssueTracker

Component used: Navigation
Version used: 1.0.0-alpha05
Devices/Android versions reproduced on: Pixel 2

When building NavDirections from ViewModels I miss a method to build a NavDirections object that represents a popBackStack or a navigateUp event for the consumer Activity/Fragment.
The objective of this feature request is to build, from ViewModel classes, Navigation Directions that have no dependency on Navigation Controllers. These navigation events can be published in a LiveData observable that Fragments and Activities can observe and consume with a Navigation Controller to navigate according to the logic implemented in the ViewModel class and leaving the Activity/Fragment completely ignorant of navigation logic.

I currently implemented this with a sealed class where I wrap popBackStack events and NavDirections into my own NavigationDirection data structure like this code below, but it will be better if this was part of the Navigation library:
/**
 * Sealed class that represents all the possible navigation destination directions that can be produced in a View Model
 */
sealed class NavigationDirection {
    object NavigateBack : NavigationDirection()
    data class Screen(val directions: NavDirections) : NavigationDirection()
}
fun NavController.navigateToNavigationDirection(direction: NavigationDirection) {
    when (direction) {
        NavigationDirection.NavigateBack -> this.popBackStack()
        is NavigationDirection.Screen -> this.navigate(direction.directions)
    }
}

// LiveData used in ViewModels
val mutableNavigationState = SingleLiveEvent<NavigationDirection>()

// Consumer code in Activity/Fragment
ViewModel.navigationState.observe(viewLifecycleOwner) {
    findNavController().navigateToNavigationDirection(it)
}