java - 将 Arraylist 从 fragment 传递到其自己的 Activity

Question

我有一个构建歌曲 ArrayList 的 fragment ，我想将该 ArrayList 传递给该 fragment 的 Activity 。我知道我可以使用界面，但不确定如何做到这一点

public class SongsListFragment extends Fragment
{

    public interface passArrayList {
            public void onArticleSelected(Uri articleUri);    
            // from android guide i don't know what to do
    }


}

这是我到目前为止所得到的，请让我知道为什么我得到 NullPointer

在主 Activity 上

    @Override
    public void onFragmentSetSongs(ArrayList<Song> songs){
        songsArrayList = songs;
    }

    @Override
    public void onSongListItemClick(int position) {
        musicService.setSong(position);
        Song playSong = songsArrayList.get(position);
        txtCurrentSongTitle.setText(playSong.getTitle());
        txtCurrentSongTitle.requestFocus();
        musicService.playSong(); 

        btnPlayPause.setImageDrawable(getResources().getDrawable(R.drawable.ic_action_pause));

        if (playbackPaused) {
            playbackPaused = false;
        }

        //setDownloaded();

    }

在 fragment 上

OnFragmentInteractionListener  songsCallBack;
OnFragmentInteractionListener  songsItemClick;

public interface OnFragmentInteractionListener {
    public void onFragmentSetSongs(ArrayList<Song> s);
    public void onSongListItemClick(int position);

}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

    // This makes sure that the container activity has implemented
    // the callback interface. If not, it throws an exception
    try {
        songsCallBack = (OnFragmentInteractionListener) getActivity();
        songsItemClick = (OnFragmentInteractionListener) getActivity();
    } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " must implement OnHeadlineSelectedListener");
    }
}

@Override
public void onDetach() {
    super.onDetach();
    songsCallBack = null;
    songsItemClick=  null;
}

listView = (ListView) root.findViewById(R.id.listViewSongs);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                songsItemClick.onSongListItemClick(position);
            }
        });

在我完成构建 SongArrayList 的方法上，我做到了

songsCallBack.onFragmentSetSongs(songArrayList);

点击ListView时出错

at com..activities.MainActivity.onSongListItemClick(MainActivity.java:107)
            at com..fragments.SongsListFragment$1.onItemClick(SongsListFragment.java:194)
            at android.widget.AdapterView.performItemClick(AdapterView.java:308)
            at android.widget.AbsListView.performItemClick(AbsListView.java:1478)
            at android.widget.AbsListView$PerformClick.run(AbsListView.java:3480)

错误位置

 musicService.setSong(position);       //Main Activity (MainActivity.java:107)

 public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            songsItemClick.onSongListItemClick(position);  < --  here
 }

Answer 1

更改界面名称，使其以大写字母开头。然后在您的 Activity 中添加以下行到您的 Activity 声明中:public class FragmentActivity extends Activity Implements PassArrayList，重写接口(interface)方法。并在 fragment 中添加以下内容:

PassArrayList mCallback;


@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    mCallback = (PassArrayList) getActivity();
}

@Override
public void onDetach() {
    super.onDetach();
    mCallback = null;
}

在代码中的某个位置，当您想要将歌曲列表传递回 Activity 时，请调用 mCallback 对象上的方法 onArticleSelected() 并将其传递给此方法方法你的数组列表。然后这个数组列表将作为 Activity 中 onArticleSelected() 方法的参数，您可以用它制作任何您喜欢的东西。但不要忘记在 onDetach() 钩子(Hook)方法中取消指向 mCallback 的链接，以防止上下文泄漏