android - causing a java.IllegalStateException error, No Activity, only when navigating to Fragment for the SECOND time

Question

I am getting a very puzzling bug that I have no idea how to even begin working through.

I have a simple app with one activity, the views are implemented with Fragments. One of the fragments has a ViewPager inside of it; so I decided I that I wanted to use the getChildFragmentManager class of the v4 support library. I also had to use ActionBarSherlock, which caused a problem, because it does not ship with the v11 of the v4 library.

I fixed this by replacing the v4 support library in ABS with the v11 library, and everything compiled and appeared to be working, including the ViewPager.

Here is the strange part:

The first time the fragment with the ViewPager opens, it works properly; but the SECOND time it is navigated to, the app crashes, giving a useless stack trace. From debugging, I discovered that the problem was with the FragmentManager returned by getChildFragmentManager; it throws the No Activity error.

Does anybody have any idea what could be causing this?

I will post code that you think is relevant.

Thank you, David

Answer 1

I followed the link in jeremyvillalobos answer (which was very helpful) that led me to this workaround.

public class CustomFragment extends Fragment {
    private static final Field sChildFragmentManagerField;

    static {
        Field f = null;
        try {
            f = Fragment.class.getDeclaredField("mChildFragmentManager");
            f.setAccessible(true);
        } catch (NoSuchFieldException e) {
            Log.e(LOGTAG, "Error getting mChildFragmentManager field", e);
        }
        sChildFragmentManagerField = f;
    }

    @Override
    public void onDetach() {
        super.onDetach();

        if (sChildFragmentManagerField != null) {
            try {
                sChildFragmentManagerField.set(this, null);
            } catch (Exception e) {
                Log.e(LOGTAG, "Error setting mChildFragmentManager field", e);
            }
        }
    }

    ...
}

It works for me well, without the need to reinstantiate the fragment.