Question

当我们执行popBackStack并返回后一堆栈中的前一个片段时，方法onViewCreated(View view, Bundle bundle)中的bundle始终为null，因为之前未调用onSaveInstanceState(Bundle outState) 。因此，当我们返回时，bundle为null并再次创建演示者（和视图状态）。在这种情况下，我们如何重用presenter和view状态（而不是重新创建它）？

您可以在下面看到一个虚拟示例。有一个带2个按钮的片段。一个按钮打开一个新片段，另一个按钮转到上一个按钮。当您返回时，将重新创建演示者和视图状态。这不是我需要的，但我在上面描述了为什么它会根据库中的代码而发生。有没有办法确保我们回去时重用演示者和查看状态？

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();
}
}

Answer 1

这个图书馆的创建者回答了这个问题here。简短的回答：“这种行为并非有意”。

Mosby 3 MVP - 当回到后栈中的片段时，总是重新创建演示者

1 个答案: