How to get navController inside activity?

Question

I use Jetpack Navigation for navigating between fragments and activity. So, I have a MainActivity with a FragmentContainerView in the layout. I can easily navigate from fragment to fragment/activity. But, I can't find a way how to navigate from one activity to another activity/fragment with navController.

For example, from fragment FA, I call navController.navigate() to activity A. Now, I want to navigate from activity A to activity B or fragment FB.

I already tried this:

val host = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
val navController = host.navController

But always got this error

null cannot be cast to non-null type androidx.navigation.fragment.NavHostFragment

Thanks!

Answer 1

A note from the navigation component guide

Note: The Navigation component is designed for apps that have one main activity with multiple fragment destinations. The main activity is associated with a navigation graph and contains a NavHostFragment that is responsible for swapping destinations as needed. In an app with multiple activity destinations, each activity has its own navigation graph.

You shouldn't use the navigation component to navigate from one activity to another. It is made to swap fragments on a Fragment container.

You can get navController inside activity using

val navHostFragment =
        supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
val navController = navHostFragment.navController

You also have to add android:name="androidx.navigation.fragment.NavHostFragment" to your fragment container

<androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
/>