onDestory,onDetach called when opening the fragment

Question

I was developing an app that became quite big in code when I noticed this problem, so I made a test app that contains a bottom navigation bar with main activity and three fragments (F1,F2,F3) and set it up with navigation component. I logged the life-cycle events of the first fragment like below and this is what I got:

public class F1 extends Fragment {

    private OnFragmentInteractionListener mListener;
    private static final String TAG = "F1";
    public F1() {
    }


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate: ");

    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Log.d(TAG, "onActivityCreated: ");
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy: ");
    }

    @Override
    public void onDetach() {
        super.onDetach();
        Log.d(TAG, "onDetach: ");
    }

    @Override
    public void onResume() {
        super.onResume();
        Log.d(TAG, "onResume: ");
    }

    @Override
    public void onStop() {
        super.onStop();
        Log.d(TAG, "onStop: ");
    }

    @Override
    public void onStart() {
        super.onStart();
        Log.d(TAG, "onStart: ");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        Log.d(TAG, "onCreateView: ");
        return inflater.inflate(R.layout.fragment_f1, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        Log.d(TAG, "onViewCreated: ");
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        Log.d(TAG, "onDestroyView: ");
    }

    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        void onFragmentInteraction(Uri uri);
    }
}

When navigating from f1 to f2 the logcat:

2019-09-22 14:11:34.648 6580-6580/com.example.navtest D/F1: onStop: 
2019-09-22 14:11:34.648 6580-6580/com.example.navtest D/F1: onDestroyView:

When navigating from f2 back to f1 using the nav bar:

2019-09-22 14:12:41.406 6580-6580/com.example.navtest D/F1: onCreate: 
2019-09-22 14:12:41.406 6580-6580/com.example.navtest D/F1: onCreateView: 
2019-09-22 14:12:41.408 6580-6580/com.example.navtest D/F1: onViewCreated: 
2019-09-22 14:12:41.408 6580-6580/com.example.navtest D/F1: onActivityCreated: 
2019-09-22 14:12:41.408 6580-6580/com.example.navtest D/F1: onStart: 
2019-09-22 14:12:41.408 6580-6580/com.example.navtest D/F1: onResume: 
2019-09-22 14:12:41.410 6580-6580/com.example.navtest D/F1: onDestroy: 
2019-09-22 14:12:41.410 6580-6580/com.example.navtest D/F1: onDetach:

Can anybody explain this behavior please? The app works normal and the fragment is visible and functions normally so why is onDestory/onDetach being called? Could it be a bug or what? I've had it in both projects and the common thing between them is how i Set up the bottom app bar in the main activity which is the normal way but I'll post it anyway:

NavController navController = Navigation.findNavController(this, R.id.navHostFragment);
BottomNavigationView appBar = findViewById(R.id.appBar);
NavigationUI.setupWithNavController(appBar, navController);

EDIT: Fragment one tested above was the start destination, logging fragment two every thing seems normal, it's only when I assign it (fragment 2) as the start destination fragment one acts as expected and fragment two shows the weird behavior. I think the issue is specifically about the starting destination fragment.

fragment2 is empty and the logcat is filtered by fragment one's tag — Hadi, Sep 22 '19 at 12:34
Could you add information about the references to the log? I'd assume there's actually two instances of F1 — tynn, Sep 22 '19 at 16:27
i dont do it manually just using the bottom nav. Actually I just tried logging the life-cycle of the destination graph of this codelab provided by google and it gave the same weird result. — Hadi, Sep 23 '19 at 13:43
https://codelabs.developers.google.com/codelabs/android-navigation/ — Hadi, Sep 23 '19 at 13:43

score 1 · Answer 1 · answered Sep 22 '19 at 12:14

1

Did you check your "TAG" on both fragment??....you may have given value F1 for TAG on both F1 and F2 fragments...

In any other cases this behavior is not expected...so if your app is not facing any problem then TAG may only be the case

answered Sep 22 '19 at 12:14

unownsp

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1

fragment2 is empty and the logcat is filtered by fragment one's tag – Hadi Sep 22 '19 at 12:34

onDestory,onDetach called when opening the fragment

1 Answers1