How to remove an observer from livedata so it doesn't show twice when navigating back to the fragment

Question

I have a fragment which displays a popup when the user is successfully logged in. If I navigate to a new fragment and come back, the popup with the previous username is shown again. I fixed this problem using SingleLiveEvent, but I now have to refactor my code to use MediatorLiveData as my data can come from 2 sources (remote and database), and it is not compatible with SingleLiveEvent.

I tried using an event wrapper and removing observers on onDestroyView() but so far nothing is working, the livedata onChanged function keeps getting called when I move back to the fragment. Here is some of my fragment:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    binding = FragmentDashboardBinding.inflate(inflater, container, false);
    binding.setLifecycleOwner(getActivity());

    //Get the attendanceViewModel for registering attendance
    attendanceViewModel = ViewModelProviders.of(this).get(AttendanceViewModel.class);
    attendanceViewModel.getAttendance().observe(getViewLifecycleOwner(), attendanceAndMember -> {
        if (attendanceAndMember != null && attendanceAndMember instanceof AttendanceMemberModel) {
            clokedInOutMember = attendanceAndMember.member;
        }
        showResultClockInOutPopup();
    });

    return binding.getRoot();
}

private void showResultClockInOutPopup() {

    clockInBuilder = new AlertDialog.Builder(getActivity());

    View view = getLayoutInflater().inflate(R.layout.status_clock_in_out_popup, null);
    TextView responseClockInOut = view.findViewById(R.id.responseClockInOut);
    Button dismissButton = view.findViewById(R.id.dismissButton);

    //Setup Popup Text
    if (clokedInOutMember != null) {
        if (StringToBool(clokedInOutMember.is_clocked_in_temp)) {
            responseClockInOut.setText("Bienvenue " + clokedInOutMember.name + ", tu es bien enregistré(e).");
        } else {
            responseClockInOut.setText("Désolé de te voir partir " + clokedInOutMember.name + ", à bientôt!");
        }
    } else {
        responseClockInOut.setText("Oups, il semblerait qu'il y ait une erreur...\n Essaye à nouveau.");
    }

    [..SETUP ALERTDIALOG...]

        //Dismiss popup
        dismissButton.setOnClickListener(v -> {
            clockInResultDialog.dismiss();
            clockInResultPopupShowed = false;
            clokedInOutMember = null;
        });

        clockInResultDialog.show();
        clockInResultPopupShowed = true;
    }

}

@Override
public void onDestroyView() {
    attendanceViewModel.getAttendance().removeObservers(this);
    super.onDestroyView();
}

And here is my ViewModel, I have to use transformations as I am getting the userId from the fragment, passing to the Viewmodel which passes it to the repository for query (maybe there is a better way?):

public class AttendanceViewModel extends AndroidViewModel {

private AttendanceRepository repository = AttendanceRepository.getInstance();
public LiveData<AttendanceMemberModel> mAttendanceAndMember;
private MutableLiveData<String> mId =  new MutableLiveData<>();

private MediatorLiveData<AttendanceMemberModel> mObservableAttendance = new MediatorLiveData<AttendanceMemberModel>();
{
    mObservableAttendance.setValue(null);

    mAttendanceAndMember = Transformations.switchMap(mId, id -> {
        return repository.saveAttendance(id);
    });

    mObservableAttendance.addSource(mAttendanceAndMember, mObservableAttendance::setValue);
}


public AttendanceViewModel(@NonNull Application application) {
    super(application);
}

public LiveData<AttendanceMemberModel> getAttendance() {
    return mObservableAttendance;

}

public void setMemberId(String id) {
    mId.setValue(id);
}


@Override
protected void onCleared() {
    mObservableAttendance.setValue(null);
    super.onCleared();
}
}

Answer 1

I can suggest you two ways. First create a boolean variable whether dialog is shown in Fragment and after showing dialog set it to true and before showing dialog check if dialog is shown. Second way is after showing dialog set livedata value to null and check if observer value null before showing dialog. I prefer second way.