How to have an Activity notify a Fragment that the back button has been pressed

Question

I have been researching this for a few days and have yet to find a working solution. There is lots of information available but because of my inexperience with Android I can't get any of the suggestions to work.

I have an Activity with a stack of 3 Fragments on top of it all of which are presented using FragmentManager Transactions and added to the backstack. While the third Fragment is active, I need to intercept the onBackPressed() method and perform some extra stuff before the Fragment is destroyed.

I have tried using Callbacks and Interfaces to capture onBackPressed() at the Activity and send it to the 3rd Fragment with no luck.

What is the proper way to have a Fragment deep in the stack watch for the Activity's onBackPressed() method.

Let me know if this is not clear.

Thanks for the help.

Answer 1

This is the post that answered my question. For a Android newbie, this told me where everything needed to go.

https://stackoverflow.com/a/30865486/2640458

The Fragment that needed to see the onBackPress() method from it's activity:

public class RatingFragment extends Fragment implements ContentActivity.OnBackPressedListener  {

@Override
public void doBack() {
    getFragmentManager().popBackStack();
}

The very important subscription to the listener in the above Fragment:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_rating, container, false);

    ((ContentActivity)getActivity()).setOnBackPressedListener(this);
}

The Activity that needs to send the onBackPress() method to the above Fragment:

public class ContentActivity extends Activity {

protected OnBackPressedListener onBackPressedListener;

public interface OnBackPressedListener {
    void doBack();
}

public void setOnBackPressedListener(OnBackPressedListener onBackPressedListener) {
    this.onBackPressedListener = onBackPressedListener;
}

@Override
public void onBackPressed() {
    if (onBackPressedListener != null)
        onBackPressedListener.doBack();
    else
        super.onBackPressed();
}

@Override
protected void onDestroy() {
    onBackPressedListener = null;
    super.onDestroy();
}
}