Multiple/Nested NavHostFragments - Jetpack Navigation

Question

I have two NavHostFragments, one in an activity which is the startDestination and another one in a Fragment. I can't seem to make the Bottom Navigation work in the Fragment with a NavHostFragment.

nav_graph.xml (The first nav_graph) (MainActivity)

nav_graph_main.xml (The second navgraph) (Fragment)

NavigationFragment.java (The one that contains the second NavHostFragment)

public class NavigationFragment extends Fragment {
    FragmentNavigationBinding binding;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        binding = DataBindingUtil.inflate(inflater, R.layout.fragment_navigation, container, false);
        View view = binding.getRoot();

        NavController navController = Navigation.findNavController(getActivity(), R.id.fragment_navigation_navHostFragment);
        NavigationUI.setupWithNavController(binding.fragmentNavigationBtmNav, navController);

        return view;
    }
}

fragment_navigation.xml

<fragment
        android:id="@+id/fragment_navigation_navHostFragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:defaultNavHost="false"
        app:layout_constraintBottom_toTopOf="@id/fragment_navigation_btmNav"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/nav_graph_main"/>

<com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/fragment_navigation_btmNav"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        app:menu="@menu/bottom_navigation"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>

bottom_navigation.xml (Menu)

<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:id="@+id/homeFragment"
        android:icon="@drawable/ic_home"
        android:title="Home" />

    <item
        android:id="@+id/notificationFragment"
        android:icon="@drawable/ic_notification"
        android:title="Notification" />

    <item
        android:id="@+id/waterLevelFragment"
        android:icon="@drawable/ic_water_level"
        android:title="Water Level Map" />

</menu>

The Main Activity has the 1st NavHostFragment. Eventually, the user will be able to reach the NavigationFragment. Once the NavigationFragment has been navigaten into, in the NavigationFragment there is a 2nd NavHostFragment with a BottomNavigationView. I would like that to work. So far, I have only seen examples of BottomNavigation inside an Activity, not Fragment.

The NavigationFragment.java I have right now throws an error when I navigate into it:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.pup.ccis.mmReady, PID: 20253
java.lang.IllegalArgumentException: ID does not reference a View inside this Activity
    at androidx.core.app.ActivityCompat.requireViewById(ActivityCompat.java:371)
    at androidx.navigation.Navigation.findNavController(Navigation.java:58)
    at com.pup.ccis.mmReady.view.main.NavigationFragment.onCreateView(NavigationFragment.java:39)
    at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2963)
    at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:518)
    at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
    at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
    at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2106)
    at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002)
    at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:524)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6077)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)

And I think that this is because it is getting the Activity instead of the Fragment. I don't know any ways to pass the Fragment to findNavController method.

So basically I have something like this:

--MainActivity (contains 1st NavHostFragment for nav_graph.xml)
|--LoginFragment
|--RegisterFragment
|--MainFragment
|--NavigationFragment (contains 2nd NavHostFragment for nav_graph_main.xml)
  |--HomeFragment
  |--NotificationFragment
  |--WaterLevelFragment

Answer 1

I'm fairly certain I ran into the same issue in the nested NavHostFragment's scenario. It turned out that I seemed to query for nav controller too early in fragments lifecycle. It would find the top level one instead of the one in the current fragment. I solved it by moving setting up the bottom nav with nav controller from onViewCreated to onActivityCreated callback (even though the latter is now deprecated)