Mosby 3 MVP - presenter is always recreated when go back to the fragment in the back stack

Hello, I discribed the problem on stackoverflow first, but didn’t get the response so far. So, ask my question here.

When we do popBackStack and return to the previous fragment in the back stack, the bundle in the method onViewCreated(View view, Bundle bundle) is always null due to the fact that onSaveInstanceState(Bundle outState) wasn’t called before. So, when we go back, bundle is null and a presenter (and view state) is created again. How in this case we can reuse presenter and view state (and not recreate it)?

You can see a dummy example below. There is a fragment with 2 buttons. One button opens a new Fragment and another button goes to the previous one. When you go back, presenter and view states are recreated. That’s not I need, but I described above why it’s happenning according to the code in the library. Is there a way to ensure that we reuse presenter and view state when we go back?

public class FirstFragment extends MvpViewStateFragment<FirstFragmentView, FirstFragmentPresenter, FirstFragmentViewState> {

public static final String TAG = "TAG";

private Button moveToAnotherFragmentButton;
private Button moveBackButton;

@Nullable
@Override
public View onCreateView(final LayoutInflater inflater, @Nullable final ViewGroup container, @Nullable final Bundle savedInstanceState) {
    final View rootFragmentView = inflater.inflate(R.layout.first_fragment, container, false);
    moveToAnotherFragmentButton = (Button) rootFragmentView.findViewById(R.id.first_fragment_go_to_another_fragment_button);
    moveBackButton = (Button) rootFragmentView.findViewById(R.id.first_fragment_back_button);
    return rootFragmentView;
}

@Override
public void onViewCreated(@NonNull final View view, @Nullable final Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    moveToAnotherFragmentButton.setOnClickListener(ignored -> addToStack(FirstFragment.class));
    moveBackButton.setOnClickListener(ignored -> getFragmentManager().popBackStack());
}

@Override
@NonNull
public FirstFragmentPresenter createPresenter() {
    Log.e(TAG, "createPresenter");
    return new FirstFragmentPresenter();
}

@NonNull
@Override
public FirstFragmentViewState createViewState() {
    Log.e(TAG, "createViewState");
    return new FirstFragmentViewState();
}

@Override
public void onNewViewStateInstance() {
    Log.e(TAG, "onNewViewStateInstance");
}

private void addToStack(@NonNull final Class<? extends Fragment> fragmentClass) {
    final FragmentManager fragmentManager = getFragmentManager();
    if (fragmentManager.isDestroyed()) {
        throw new UnexpectedException("FragmentManager is destroyed");
    }

    final Fragment fragment = Fragment.instantiate(getContext(), fragmentClass.getName());

    final FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);

    fragmentTransaction.replace(R.id.activity_main_content_container, fragment, null)
            .addToBackStack(null)
            .commit();
}
}```

[sockeqwe]

Hi, sorry, not yet. Most likely I have time at end August to work on that…

On Do., 17. Aug. 2017, 18:52 Thomas Vos [e-mail] wrote:

@sockeqwe https://github.com/sockeqwe Hi Hannes, have you had a chance to work on the new presenter implementation? Could you share your idea about on how you are going to implement it? If you have a snapshot ready, I’ll be glad to help with testing. Thanks, Thomas

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[sockeqwe]

Since this is mostly yet another Presenter implementation I try to find some time for it this week. Its not like moxy which needs an entirely framework and tools like annotation processing around it.

Thomas Vos [e-mail] schrieb am Mo., 24. Juli 2017, 16:50:

@sockeqwe https://github.com/sockeqwe Thanks for an explanation about the back stack. If Mosby 3.1 adds adds support for a “queue” it would be great! How would you recommend me implementing my code, until the new 3.1 approach, so it will be easy to migrate?

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