@Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        rootRequestManagerFragment = RequestManagerRetriever.get()
                .getRequestManagerFragment(getActivity().getFragmentManager());
        if (rootRequestManagerFragment != this) {
            rootRequestManagerFragment.addChildRequestManagerFragment(this);
        }
    }
Returns true if the fragment is a descendant of our parent.
core/src/main/java/com/bumptech/glide/manager/RequestManagerFragment.java