如何从内存和SD卡获取所有.MP3文件

Question

我正在尝试从移动设备获取所有Mp3文件并将其显示在列表视图中。我能够从模拟器的SD卡中获取特定文件中的歌曲，但是当我尝试获取所有文件时它没有显示任何歌曲。我试过两种方法

1.`

public class MainActivity extends ListActivity {
final String MEDIA_PATH = Environment.getExternalStorageDirectory()
        .getPath() + "/";
private ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
private String mp3Pattern = ".mp3";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    updatelist();
}
public ArrayList<HashMap<String, String>> getPlayList() {
    System.out.println(MEDIA_PATH);
    if (MEDIA_PATH != null) {
        File home = new File(MEDIA_PATH);
        File[] listFiles = home.listFiles();
        if (listFiles != null && listFiles.length > 0) {
            for (File file : listFiles) {
                System.out.println(file.getAbsolutePath());
                if (file.isDirectory()) {
                    scanDirectory(file);
                } else {
                    addSongToList(file);
                }
            }
        }
    }
    // return songs list array
    return songsList;
}

private void scanDirectory(File directory) {
    if (directory != null) {
        File[] listFiles = directory.listFiles();
        if (listFiles != null && listFiles.length > 0) {
            for (File file : listFiles) {
                if (file.isDirectory()) {
                    scanDirectory(file);
                } else {
                    addSongToList(file);
                }

            }
        }
    }
}

private void addSongToList(File song) {
    if (song.getName().endsWith(mp3Pattern)) {
        HashMap<String, String> songMap = new HashMap<String, String>();
        songMap.put("songTitle",
                song.getName().substring(0, (song.getName().length() - 4)));
        songMap.put("songPath", song.getPath());

        // Adding each song to SongList
        songsList.add(songMap);
    }
}

private void updatelist(){
ArrayAdapter<String> songMp =new ArrayAdapter<String>(this,R.layout.content_main,songsList);
setListAdapter(songMp);
}

}

` 2

public class MainActivity extends ListActivity {
private ListView listView;
final String MEDIA_PATH = Environment.getExternalStorageDirectory()
        .getPath() + "/";
private List<String> songsList = new ArrayList< String>();
private String mp3Pattern = ".mp3";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    listView=(ListView)findViewById(android.R.id.list);
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

        }
    });
    updatePlaylist();
}
class Mp3Filter implements FilenameFilter{
    @Override
public boolean accept(File dir, String filename) {
    return (filename.endsWith(mp3Pattern));
}
}
private void updatePlaylist(){
    File home = Environment.getExternalStorageDirectory();
    if (home.listFiles(new Mp3Filter()).length>0){
        for (File file:home.listFiles(new Mp3Filter())){
            songsList.add(file.getName());
        }
        ArrayAdapter<String> song =new ArrayAdapter<String>(this,android.R.layout.simple_expandable_list_item_1,songsList);
        setListAdapter(song);
    }
}
}

有人可以告诉我我在其中任何一个方面做错了。我在第一个中出错了，在第二个中我得到了一个空白的活动 提前任何示例或提示都足够了。