ArrayAdapter.add方法UnsupportedOperationException

        List<String> planets = new ArrayList<String>();
        mUserListAdapter = new ArrayAdapter<String>(
                getActionBar().getThemedContext(),
                android.R.layout.simple_list_item_activated_1,
                android.R.id.text1,
                planets
        );
         mUserListAdapter.add("Now I Can Add");