getSupportActionBar from inside of Fragment ActionBarCompat

After Fragment.onActivityCreated(…) you’ll have a valid activity accessible through getActivity().

You’ll need to cast it to an ActionBarActivity then make the call to getSupportActionBar().

((AppCompatActivity)getActivity()).getSupportActionBar().setSubtitle(R.string.subtitle);

You do need the cast. It’s not poor design, it’s backwards compatibility.