Where to call getChildFragmentManager()?

Question

Problem

According to the Google's docs:

You can now embed fragments inside fragments. This is useful for a variety of situations in which you want to place dynamic and re-usable UI components into a UI component that is itself dynamic and re-usable. For example, if you use ViewPager to create fragments that swipe left and right and consume a majority of the screen space, you can now insert fragments into each fragment page. To nest a fragment, simply call getChildFragmentManager() on the Fragment in which you want to add a fragment. This returns a FragmentManager that you can use like you normally do from the top-level activity to create fragment transactions. For example, here’s some code that adds a fragment from within an existing Fragment class:

Fragment videoFragment = new VideoPlayerFragment();
FragmentTransaction transaction = getChildFragmentManager().beginTransaction();
transaction.add(R.id.video_fragment, videoFragment).commit();

So I had (for example) TestFragment which looks like:

public class TestFragment extends Fragment {

    private View mFragmentView;
    private FrameLayout mFrameLayout;   

    public HistoryFragment() {
        super();
    }       

    @Override   
    public View onCreateView(LayoutInflater pInflater, ViewGroup pViewGroup, Bundle pBundle) {          

        mFragmentView = pInflater.inflate(R.layout.fragment_layout, pViewGroup, false);         

        mFrameLayout = (FrameLayout) mFragmentView.findViewById(R.id.framelayout);

        return mFragmentView;
    }   

    public void onDestroyView() {
        super.onDestroyView();
    }    

    /* ISSUE */
    public void doSomethingSpecial() {
        FragmentManager tFragmentManager = getChildFragmentManager();
    }
}

At the MainActivity I initialize my fragment like:

mTestFragment = new TestFragment();
mTestFragment.doSomethingSpecial();

Then I pass fragment to ViewPager via FragmentPagerAdapter.

Finally, I get an exception. But if I use only:

mTestFragment = new TestFragment();

Then it works.

Question

Where should I call getChildFragmentManager() method in my fragment? What I am doing wrong?

If you have a good example of using new Android Nested Fragments please share link with me. I would greatly appreciate for your help.

Independent

Take a look at this link ... getChildFragment() on Programmatically added fragments – Mere

Answer 1

Short answer: I call and use getChildFragmentManager() in my Fragment's onViewCreated() method.

For example:

@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    addInnerFragment(); // This method does the getChildFragmentManager() stuff.
}

Telles

Answer 2

Actually I Just used in the following case.

I was trying to add a Map into a ViewPager. As you may know, the "pages" in the ViewPager are Fragments, so I was unable to use this code Sample using maps from an Activity. I was trying to get the SupportMapFragment from the Activity doing things like:

SupportMapFragment mapView = (SupportMapFragment) getActivity().getSupportFragmentManager().findFragmentById(R.id.map);

But mapView was always null, so my application crashes.

I found the following answer and works inmediatly.

This can be an useful example where to use getChildFragmentManager()

Hope this can be helpful.

Milled

Your first link is broken and the second link doesn't provide any insight on where to use getChildFragmentManager(). :-( – Telles

That was a last year answer :/ You could edit the answer and provide feedback instead of down-voting – Milled

I'm not sure what code the link contained, so couldn't really edit your answer. I felt the answer wasn't useful, hence the downvote - but at least I left a comment! :-) – Telles

Answer 3

According to the docs, this method:

Return a private FragmentManager for placing and managing Fragments inside of this Fragment.

So you can use it if you want to add/replace a new fragment to your existing fragment, you should commit your TestFragment transaction first, then add the inner fragment to it. try something like this:

    TestFragment mTestFragment = new TestFragment();
//get the activity's fragment manager to add the fragment
    FragmentTransaction transaction= getFragmentManager().beginTransaction();
    transaction.add(R.id.container, mTestFragment).commit();
    //add the inner fragment
    mTestFragment.doSomethingSpecial();

Pliam