public void onBookListChanged() {
   mBarTabManager.switchTab(tab_collection);
   CollectionFragment frag = (CollectionFragment) tab_collection.getFragment();
   if (frag != null) frag.refreshBookList();
 }
 @Override
 public void confirmDelete(int id) {
   CollectionFragment frag = (CollectionFragment) tab_collection.getFragment();
   if (frag != null) frag.deleteBook(id);
 }