片段之间的Android通信

http://pastebin.com/p9FCCMX1I正在尝试通过活动将数据从一个片段发送到另一个片段。可以将数据从GroupFragment发送到ChatActivity（id包含正确的值），但是当到达时：

@Override
public void respond(String id) {
    interfaceDataCommunicatorFromActivity.respond(id);
}

在我的ChatActivity中，它抛出NUllPointException，我不知道如何使其工作？

（当我只粘贴部分代码时，我试图使您更容易阅读，如果没有帮助，它会友好并纠正我！对于所有代码：“ http://pastebin.com/p9FCCMX1 ”）

ChatActivity：

public class ChatActivity extends Activity implements
    GroupFragment.OnFragmentInteractionListener,
    //ChatFragment.OnFragmentInteractionListener,
    GroupFragment.InterfaceDataCommunicator {

    public InterfaceDataCommunicatorFromActivity interfaceDataCommunicatorFromActivity;

    @Override
    public void respond(String id) {
        interfaceDataCommunicatorFromActivity.respond(id);
    }

    public interface InterfaceDataCommunicatorFromActivity {
        public void respond(String id);
    }
}

GroupFragment：

public class GroupFragment extends Fragment {
    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";
    public InterfaceDataCommunicator interfaceDataCommunicater;
    ...../


    public void CreateNewGroup(String groupName) {

        Map<String, Group> newGroup = new HashMap<>();

        Firebase  firebaserootRef = new Firebase("https://luminous-heat-420.firebaseio.com");

        Firebase firebaseGroup = firebaserootRef.child("").push();

        Group group = new Group();

        group.SetID(firebaseGroup.getKey());
        group.SetName(groupName);

        String id = firebaseGroup.getKey();
        firebaseGroup.child("id").setValue(group.GetId());
        firebaseGroup.child("name").setValue(group.GetName());

        newGroup.put(id, group);

        interfaceDataCommunicater.respond(group.GetId());
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            mListener = (OnFragmentInteractionListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnFragmentInteractionListener");
        }

        try {
            interfaceDataCommunicater = (InterfaceDataCommunicator) activity;
        } catch (ClassCastException c) {
            throw new ClassCastException(activity.toString()
                    + " must implement InterfaceDataCommunicator");
        }
    }

    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        public void onFragmentInteraction(Uri uri);
    }

    public interface InterfaceDataCommunicator{
        public void respond(String id);
    }
}

聊天片段：

public class ChatFragment extends Fragment implements
    View.OnClickListener,
    ChatActivity.InterfaceDataCommunicatorFromActivity {

    public ChatActivity.InterfaceDataCommunicatorFromActivity
           interfaceDataCommunicatorFromActivity; 

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            mListener = (OnFragmentInteractionListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnFragmentInteractionListener");
        }

        try {
            interfaceDataCommunicatorFromActivity = (ChatActivity
               .InterfaceDataCommunicatorFromActivity) activity;    
        } catch (ClassCastException c) {
            throw new ClassCastException(activity.toString()
                    + " must implement InterfaceDataCommunicator");
        }
    }


    public interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        public void onFragmentInteraction(Uri uri);
    }

    @Override
    public void respond(String id) {
        this.groupID = id;
    }
}