How to determine back button press

Question

I am using android navigation components library. I have two fragments set up with navigation graph. I want to do some additional actions on back button press inside of my fragment.

override fun onOptionsItemSelected(item: MenuItem): Boolean {
    return NavigationUI.onNavDestinationSelected(item, view!!.findNavController())
           || super.onOptionsItemSelected(item)
}

I use this code to handle toolbar up button click, but I also want to handle back button press. How can I do this?

Look at https://stackoverflow.com/questions/7992216/android-fragment-handle-back-button-press page. You will find your answer there. — Mir Milad Hosseiny, Apr 07 '19 at 15:01
I want to notify my viewmodel about leaving fragment to save data — Vladislav, Apr 07 '19 at 15:22
This is what you want https://stackoverflow.com/questions/51043428/handling-back-button-in-android-navigation-component — John Joe, Apr 07 '19 at 15:26
the on back pressed should be handlet only in the [activity](https://medium.com/@stavro96/how-to-setup-android-navigation-component-with-drawer-88b833312661) — coroutineDispatcher, May 03 '19 at 08:33

keepTrackOfYourStack · Answer 1 · 2019-04-07T15:06:36.013

0

It is another override onBackPessed

back press

edited Apr 07 '19 at 15:06

answered Apr 07 '19 at 14:52

keepTrackOfYourStack

1,235
9
22

It won't work in fragment, you need some tricks to handle it. – Mir Milad Hosseiny Apr 07 '19 at 15:00
added a link to the answer – keepTrackOfYourStack Apr 07 '19 at 15:07

score 0 · Answer 2 · answered May 03 '19 at 08:32

Example:

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 boolean handleOnBackPressed() {
                // Handle the back button event
            }
        });
        requireActivity().getOnBackPressedDispatcher().addCallback(this, callback);

        // The callback can be enabled or disabled here or in handleOnBackPressed()
    }
    ...
}

More explanations in android official guide: Provide custom back navigation

How to determine back button press

2 Answers2