为什么Parse Query Adapter总是空的？

Question

我正在尝试使用解析查询适配器填充列表，但它始终为空。我正在按照解析（https://parse.com/tutorials/parse-query-adapter）提供的教程。如果我做错了，请告诉我。我怎样才能使它工作？谢谢

public class BrandsFragment extends Fragment {
 private ParseQueryAdapter mainAdapter;

 @Override
 public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);
    mainAdapter = new ParseQueryAdapter(getActivity(), "Brands");
    mainAdapter.setTextKey("BrandName");
 }

  @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_brands, container, false);

    ListView listFollowingView = (ListView) rootView.findViewById(R.id.brands_list);
    brands_list.setAdapter(mainAdapter);
    mainAdapter.loadObjects();

    if(mainAdapter.isEmpty()){
        Toast.makeText(getActivity(),"EMPTY",Toast.LENGTH_SHORT).show();
    }
 }
}

布局：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.swipeit.swipeit.BrandsActivity$PlaceholderFragment">

<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/brands_list" />

</RelativeLayout>