Change toolbar from fragment

Question

I am writing an app using jetpack recommended architecture , NavigationUI, and the navigation graph . So I have one main activity with a Toolbar , a BottomNavigationView and the NavHostFragment .

Everything worked nicely until now: I need to change the Toolbar to use a CollapsingToolbarLayout and hide the BottomNavigationView in one of my fragment.

I tried to add a navigation listener (as described here ) to hide my Toolbar and BottomNavigationView , and in my fragment, I inflate the new Toolbar and call setSupportActionBar() on the main activity.

// in MainActivity.java
@Override
protected void onCreate(Bundle savedInstanceState) {
  // ...
  navController.addOnDestinationChangedListener((controller, destination, arguments) -> {
        if(destination.getId() == R.id.detailFragment){
          bottomBar.setVisibility(View.GONE);
          topBar.setVisibility(View.GONE);
        }else{
          bottomBar.setVisibility(View.VISIBLE);
          topBar.setVisibility(View.VISIBLE);
        }
      });
  // ...
}

public void changeToolbar(Toolbar toolbar){
  getSupportActionBar().hide();
  setSupportActionBar(toolbar);
}

// in DetailFragment.java
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
  Bundle savedInstanceState) {
  // ...
  navController = NavHostFragment.findNavController(this);

  AppBarConfiguration.Builder builder = new Builder(
      R.id.accuracyFragment,
      R.id.dataFragment,
      R.id.magnetFragment,
      R.id.settingsFragment);
  AppBarConfiguration config = builder.build();
  NavigationUI.setupWithNavController(toolbarLayout, toolbar, navController);
  ((MainActivity)getActivity()).changeToolbar(toolbar);
  // ...
}

It almost works correctly, but:

1. when I navigate up or go to another fragment, the BottomNavigationView is not correctly displayed. It seems to be pushed down by the Toolbar .
2. the transition is ugly: the toolbar is visibly changing, I can see it disappearing before being changed

So the question is: is there another way to change/hide the navigation elements from the fragment? If not, should I create a new activity?

Answer 1

It's been a wild ride, but I finally found a solution. For the issue number 1, this is due to the way Android manages the fitsSystemWindows property propagation. For this to work correctly, I made a few changes to my layouts. I created a custom FitSystemWindowLinearLayout , which is simply a class extending the standard LinearLayout and overriding onApplyWindowInsets like this:

  @Override
  public WindowInsets onApplyWindowInsets(WindowInsets insets) {
    int childCount = getChildCount();
    for (int index = 0; index < childCount; ++index) {
      getChildAt(index).dispatchApplyWindowInsets(insets);
    }

    return insets;
  }

My main activity now looks like this:

+-- CoordinatorLayout, fitsSystemWindows=false
    +-- FitSystemWindowLinearLayout, fitsSystemWindows="false"
        +-- Toolbar
        +-- NavHostFragment, fitsSystemWindows="false"
        +-- BottomNavigationView, fitsSystemWindows="false"

For the second issue, namely the transition being ugly, I mitigated that by adding a shared element to the transition.

All in all, I think it's easier to use a new activity for this kind of things, the NavigationUI falls a bit short for now.

Here are some resources that helped me:

• https://medium.com/androiddevelopers/why-would-i-want-to-fitssystemwindows-4e26d9ce1eec
• Android fitsSystemWindows not working when replacing fragments
• Collapsing Toolbar problems with Status Bar and Bottom Bar. Fitssystemwindows="true" not working
• fitsSystemWindows effect gone for fragments added via FragmentTransaction
• https://www.reddit.com/r/androiddev/comments/aryxvu/fitssystemwindows_misbehaves_with_navigation/ - https://medium.com/androiddevelopers/why-would-i-want-to-fitssystemwindows-4e26d9ce1eec