A: 8 - ui/example_3/parent_fragment/Example3ParentFragment.java

Example3ParentFragment.java

public final class Example3ParentFragment extends BaseFragment implements View.OnClickListener {

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

        if (savedInstanceState == null) {
            addChildFragment(R.id.child_fragment_container, new Example3ChildFragment());
        }

        ...
    }
}