Android Navigation add to back stack

Question

I tried use Android Navigation component and have a problem with back stack.

I have Fragment A, B.To navigate from A to B, I write:

Navigation.findNavController(view).navigate(R.id.a_to_b)

But how can i return back to A on back button clicked?

Answer 1

It's well known that the Nav library is supposed to take care of pushing and popping from the backstack itself. I've spent a couple of hours hunting a missing line though so thought this might help future googlers, from the basic sample:

<androidx.fragment.app.FragmentContainerView
android:id="@+id/nav_host_splash_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:defaultNavHost="true"
app:navGraph="@navigation/launch_nav_graph"
tools:context=".launch.SplashActivity" />

If you do not set the defaultNavHost, you basically need to take care of the backstack yourself. This line is crucial to automatically add fragments to the back stack.

Answer 2

The fragment A is in your backstack, so you can just implement a click listener for your button and, for example, use this solution.

It provides an example and some explanations:

New release androidx.activity ver. 1.0.0-alpha07 brings some changes

More explanations in android official guide: Provide custom back navigation ```java public class MyFragment extends Fragment {

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // This callback will only be called when MyFragment is at least Started.
    OnBackPressedCallback callback = new OnBackPressedCallback(true /* enabled by default */) {
        @Override
        public void handleOnBackPressed() {
            // Handle the back button event
        }
    };
    requireActivity().getOnBackPressedDispatcher().addCallback(this, callback);

Happy coding!