Keep getChildFragmentManager navigation stack after deleting and re-adding fragment

Question

I have activity:

`<RelativeLayout>
    <FrameLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
    <Button/>
    <Button/>
</RelativeLayout>`

Inside this container, depending on which button is pressed, FragmentA or FragmentB appear. These fragments are containers for nested child fragments. That is, each fragment contains its own navigation stack.

In onCreate of Activity, I create these 2 fragments:

fragmentA = (FragmentContainer) Fragment.instantiate(this, FragmentContainer.class.getName()); fragmentB = (FragmentContainer) Fragment.instantiate(this, FragmentContainer.class.getName());

Then I continue to replace each other:

final FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction() .replace(R.id.container, fragment); .commitAllowingStateLoss();

So far, so good, everything works. BUT

Problem:

Each time I replace fragment A with fragment B (and vice versa), getChildFragmentManager () destroys its navigation stack, and fragment A / B starts every time from scratch, and not with the nested fragment that it contained before the replacement.

? , ? ,

Answer 1

, :

MainActivity.xml

<RelativeLayout>
    <FrameLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</RelativeLayout>

MainActivity.java

public class MainActivity extends FragmentActivity {

    final FragmentContainer [] fragmentContainers = new FragmentContainer[3];
    int currentTabIndex = -1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final FragmentMetaData [] fragmentContainersMetaData = {
                new FragmentMetaData(FragmentA.class.getName(), null),
                new FragmentMetaData(FragmentB.class.getName(), null),
                new FragmentMetaData(FragmentC.class.getName(), null)
        };

        for (int i = 0; i < fragmentContainers.length; i++) {
            fragmentContainers[i] = (FragmentContainer) Fragment.instantiate(this, FragmentContainer.class.getName());
            fragmentContainers[i].addMetaData(fragmentContainersMetaData[i]);
        }

        tabPageNavigationSelection(0);
    }

    void replaceFragmentBy(final Fragment fragment) {
        FragmentManager fragmentManager = getSupportFragmentManager();                    
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.container, fragment);
        fragmentTransaction.commitAllowingStateLoss();
    }

    // Method to switch between tabs
    void tabPageNavigationSelection (final int index) {
        if (currentTabIndex == index) {
            fragmentContainers[currentTabIndex].clearStackExceptRootFragment();
        } else {
            currentTabIndex = index;
            replaceFragmentBy(fragmentContainers[currentTabIndex]);
        }
    }
}

FragmentContainer.xml

<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:background="@color/lightest_gray"
    android:id="@+id/nestedContainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

FragmentContainer.java

public final class FragmentContainer extends Fragment {
    private final List<FragmentMetaData> fragmentMetaDataStack = new ArrayList<>();

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        initialize(inflater, container, R.layout.fragment_container);

        for (FragmentMetaData metaData : fragmentMetaDataStack) {
            showNestedFragment(Fragment.instantiate(getActivity(), metaData.className, metaData.fragmentBundle), fragmentMetaDataStack.indexOf(metaData) > 0, true);
        }

        return getFragmentView();
    }

    @Override
    public void onResume() {
        super.onResume();
        if (getChildFragmentManager().getFragments() == null){
            return;
        }

        int stackDepth = getChildFragmentManager().getFragments().size();
        if (stackDepth > 0 && fragmentMetaDataStack.size() < stackDepth &&
                getChildFragmentManager().getFragments().get(fragmentMetaDataStack.size() - 1) != null) {
            getChildFragmentManager().getFragments().get(fragmentMetaDataStack.size()-1).onResume();
        }
    }

    public void showNestedFragment(final Fragment fragment, final boolean addToBackStack, final boolean isRestoring) {
        final FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.nestedContainer, fragment);
        if (addToBackStack) {
            fragmentTransaction.addToBackStack(null);
        }

        if (!isRestoring) {
            fragmentMetaDataStack.add(new FragmentMetaData(fragment.getClass().getName(), fragment.getArguments()));
        }

        fragmentTransaction.commitAllowingStateLoss();
    }

    public void onBackPressed() {
        if (getChildFragmentManager().getBackStackEntryCount() > 0) {
            getChildFragmentManager().popBackStack();
            fragmentMetaDataStack.remove(fragmentMetaDataStack.size() - 1);
        } else {
            getActivity().finish();
        }
    }

    public void addMetaData(FragmentMetaData metaData) {
        fragmentMetaDataStack.add(metaData);
    }

    public void clearStackExceptRootFragment() {
        getChildFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
        while (fragmentMetaDataStack.size() > 1) {
            fragmentMetaDataStack.remove(1);
        }
    }
}

, -, instagram:)