Proper use of sub sub fragments with (Child)FragmentManager

Question

How do I properly use Fragments in Fragments?

My (simplified) use case is following, I have an activity with a layout fragment and this fragment theirself contains a sub fragment... all fragments are added manually to their parents...

---------------------------------------------------------- - Activity                                               - -                                                        - -                                                        - -     ---------------------------------------            - -     - Fragment                            -            - -     -                                     -            - -     -    -----------------                -            - -     -    - SubFragment   -                -            - -     -    -               -                -            - -     -    -               -                -            - -     -    -----------------                -            - -     ---------------------------------------            - -                                                        - ---------------------------------------------------------- 

Now in my activity's onCreate I do following:

if (savedInstanceState == null) {     // I create the fragment     mMainFragment = new MainFragment();     FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();     transaction.replace(R.id.fragment_main, mMainFragment);     transaction.commit(); } else {     // I retrieve the fragment     mMainFragment = (BaseFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_main); } 

And in my fragments onCreate I get/create my SubFragment:

mSubFragment = getChildFragmentManager().findFragmentByTag(SubFragment.class.getName()); if (mSubFragment == null) {     mSubFragment = new SubFragment();     getChildFragmentManager().beginTransaction().add(R.id.fragment_sub, mSubFragment, SubFragment.class.getName()).commit(); } 

Problem

After screen rotation, my SubFragment is added twice... If I use the activity's FragmentManager then it works... But why does it not work with the ChildFragmentManager? Of course, the Fragment is a new fragment, but the activity is a new one as well, so why does it work with the activity's FragmentManager but not with the parent fragment's one?

In a fragment, I should use the fragments ChildFragmentManager, shouldn't I?

Answer 1

You should add SubFragment to Fragment the same way like you add Fragment to Activity. I mean adding Fragment to Activity should look like:

 @Override  public void onCreate(Bundle savedInstanceState) {    ....    if (savedInstanceState == null){       //add fragment       mMainFragment = new MainFragment();       FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();       transaction.replace(R.id.fragment_main, mMainFragment);       transaction.commit();    }  } 

Adding SubFragment to MainFragment should look like:

    public class MainFragment extends Fragment{        @Override       public View onCreateView(LayoutInflater i, ViewGroup c, Bundle savedInstanceState) {            ...         if (savedInstanceState == null){            mSubFragment = new SubFragment();             //add child fragment            getChildFragmentManager()                    .beginTransaction()                    .add(R.id.fragment_sub, mSubFragment, "tag")                    .commit();         }       }     } 

or you can add child fragment to Fragment in onCreate method