Demos using a listener for a data source and also an editable field.

AttributeExtensions.kt

val <T> T.exhaustive: T
    get() = this

ControlledNavigationPartialCode.kt

mainActivityVm.currentFragment.observe(this, Observer(::setScreen))

    private fun setScreen(screen: Screen) =
        with(findNavController(R.id.nav_host_fragment_container)) {
        when (screen) {
            Screen.SPLASH -> { /*is default and never returns here*/
            }
            Screen.FROM_SPLASH_TO_LIST -> safeNavigate(SplashFragmentDirections.actionSplashFragmentToGoalFragment())
            Screen.FROM_ADD_TO_LIST -> safeNavigate(AddGoalFragmentDirections.actionAddGoalFragmentToGoalFragment())
            Screen.ADD -> safeNavigate(GoalsListFragmentDirections.actionGoalFragmentToAddGoalFragment())
        }.exhaustive
    }
    
private fun NavController.safeNavigate(d: NavDirections) =
    currentDestination?.getAction(d.actionId)?.let { navigate(d) }
        ?: Timber.e("Invalid route for direction ${d} with id ${d.actionId}")

NavigationPartialCode.kt

private val _currentFragment = MutableLiveData<Screen>(Screen.SPLASH)

    /**
     * The current fragment is determined by two factors:
     * 1. The move from the splash screen to the main fragment happens when authentication is complete
     * 2. Any subsequent navigations are guided by code that modifies _currentFragment, the private
     *    mutable livedata.
     */
    val currentFragment: LiveData<Screen> = MediatorLiveData<Screen>().apply {
        addSource(repository.isAuthenticated) { authenticated ->
            if (authenticated) {
                value = Screen.FROM_SPLASH_TO_LIST
            }
        }
        addSource(_currentFragment) { value = it }
    }