Artifact used: android.arch.navigation:navigation-ui:1.0.0-alpha04

The Navigation Component has this very useful function to sync up menu items from a NavigationView with the NavController. It makes sure that the selected item is checked, can close the navigation drawer on selection if a DrawerLayout is used, or set the title of an ActionBar/Toolbar according to the current destination.

With the addition of the bottom app bar in Material Design we've also begun using the bottom navigation drawer (https://material.io/design/components/navigation-drawer.html#bottom-drawer). It can be implemented with a BottomSheetDialogFragment containing a NavigationView and some additional UI elements. We can then set up our NavigationView with the parent Activity's NavController from inside this dialog (simplified):

public class BottomDrawerFragment extends BottomSheetDialogFragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_bottom_drawer, container, false);
NavigationView navigationView = view.findViewById(R.id.bottom_drawer_navigation);
NavigationUI.setupWithNavController(navigationView, Navigation.findNavController(getActivity(), R.id.nav_host_fragment));
return view;
}
}

This works well, but because NavigationUI currently doesn't dismiss the BottomSheetDialogFragment when a menu item has been selected like it closes the DrawerLayout, the bottom navigation drawer remains open and needs to be dismissed in another way (which comes with additional code overhead and issues).

Since AndroidX is now part of AOSP, I took a look at the implementation and I think that support for this could be added with two lines of code (see '+' characters at beginning of lines below) by doing for the DialogFragment what is already done for the DrawerLayout (excerpt from androidx-master-dev/navigation/ui/src/main/java/androidx/navigation/ui/NavigationUI.java).

public static void setupWithNavController(@NonNull final NavigationView navigationView,
@NonNull final NavController navController) {
navigationView.setNavigationItemSelectedListener(
new NavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
boolean handled = onNavDestinationSelected(item, navController, true);
if (handled) {
ViewParent parent = navigationView.getParent();
if (parent instanceof DrawerLayout) {
((DrawerLayout) parent).closeDrawer(navigationView);
+ } else if (parent instanceof BottomSheetDialogFragment) {
+ ((DialogFragment) parent).dismiss();
}
}
return handled;
}
});
navController.addOnNavigatedListener(new NavController.OnNavigatedListener() {
@Override
public void onNavigated(@NonNull NavController controller,
@NonNull NavDestination destination) {
Menu menu = navigationView.getMenu();
for (int h = 0, size = menu.size(); h < size; h++) {
MenuItem item = menu.getItem(h);
item.setChecked(matchDestination(destination, item.getItemId()));
}
}
});
}

The most active owner of the Navigation Component is Ian Lake and it he's been adding support for more and more UI components to the NavigationUI class in the past months, so I think he's the person to talk to about this. Assuming this doesn't introduce any issues, he could probably get it done in a couple of minutes.
Alternatively, I could implement this and the accompanying test myself, contribute it and try to get it reviewed.