Exception：must implement OnFragmentInteractionListener

转载请注明出处：http://blog.csdn.net/parallelyk/article/details/51510569

今天写代码的时候发现，用Android Studio创建一个blank Fragment的时候会为我们创建一个Fragment的模板。

public class MainFragment extends Fragment {// TODO: Rename parameter arguments, choose names that match// the fragment initialization parameters, e.g. ARG_ITEM_NUMBERprivate static final String ARG_PARAM1 = "param1";private static final String ARG_PARAM2 = "param2";// TODO: Rename and change types of parametersprivate String mParam1;private String mParam2;private OnFragmentInteractionListener mListener;public MainFragment() {// Required empty public constructor}/*** Use this factory method to create a new instance of* this fragment using the provided parameters.** @param param1 Parameter 1.* @param param2 Parameter 2.* @return A new instance of fragment MainFragment.*/// TODO: Rename and change types and number of parameterspublic static MainFragment newInstance(String param1, String param2) {MainFragment fragment = new MainFragment();Bundle args = new Bundle();args.putString(ARG_PARAM1, param1);args.putString(ARG_PARAM2, param2);fragment.setArguments(args);return fragment;}@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);if (getArguments() != null) {mParam1 = getArguments().getString(ARG_PARAM1);mParam2 = getArguments().getString(ARG_PARAM2);}}@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {// Inflate the layout for this fragmentreturn inflater.inflate(R.layout.fragment_main, container, false);}// TODO: Rename method, update argument and hook method into UI eventpublic void onButtonPressed(Uri uri) {if (mListener != null) {mListener.onFragmentInteraction(uri);}}@Overridepublic void onAttach(Context context) {super.onAttach(context);if (context instanceof OnFragmentInteractionListener) {mListener = (OnFragmentInteractionListener) context;} else {throw new RuntimeException(context.toString()+ " must implement OnFragmentInteractionListener");}}@Overridepublic void onDetach() {super.onDetach();mListener = null;}/*** This interface must be implemented by activities that contain this* fragment to allow an interaction in this fragment to be communicated* to the activity and potentially other fragments contained in that* activity.* <p/>* See the Android Training lesson <a href=* "http://developer.android.com/training/basics/fragments/communicating.html"* >Communicating with Other Fragments</a> for more information.*/public interface OnFragmentInteractionListener {// TODO: Update argument type and namevoid onFragmentInteraction(Uri uri);}
}

其中有一段：

if (context instanceof OnFragmentInteractionListener) {mListener = (OnFragmentInteractionListener) context;} else {throw new RuntimeException(context.toString()+ " must implement OnFragmentInteractionListener");}

即我们的context也就是Activity必须实现OnFragmentInteractionListener。

那么OnFragmentInteractionListener是什么东西？

在一个Activity中往往有多个Fragment，他们之间是无法直接通信的，所以Fragment需要通过它们所绑定的Activity作为中介来进行通信。而OnFragmentInteractionListener就是用来实现不同Fragment之间通信的接口。OnFragmentInteractionListener在OnAttach阶段注册并复制给mListener。

使用：在Fragment中直接调用mListener.OnFragmentInteractionListener(uri)

mListener.OnFragmentInteractionListener(uri)

在Activity中通过

    @Overridepublic void onFragmentInteraction(Uri uri) {//做想要做的数据操作和通信，如给其他Fragment发送数据sendMsgTo(otherFragment,uri);}

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