code: public ActionMode checkActionMode(AppCompatActivity act) {
          int selected = mSelectExtension.getSelectedItems().size();
          return checkActionMode(act, selected);
      }
docs: check if the ActionMode should be shown or not depending on the currently selected items
  Additionally, it will also update the title in the CAB for you
  
  @param act the current Activity
  @return the initialized ActionMode or null if no ActionMode is active after calling this function