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 Fragme

Answer 1

sadly, it's a bug of support v4, still there :(

When you choose other Fragment via Navigation Drawer or other thing like it, the fragment which has sub-fragments is detached. So those sub-fragments' fragmentManager(getChildFragmentManager()) is no longer exist. while those fragments return, error occurred. Bomb!

Obviously, support v4 should clean mChildFragmentManager in onDetach(), but it didn't, so we must depend on ourselves. such as following codes in the fragment which has sub-fragments:

@Override
    public void onDetach() {
        try {
            Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");
            childFragmentManager.setAccessible(true);
            childFragmentManager.set(this, null);
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        super.onDetach();
    }

Everything will be OK, have a good day :)