我开始重复播放mp3音乐文件的MediaPlayer，但它正在体验音乐扫描

Question

我正在尝试创建一个媒体播放MP3播放器，但它正在犯错误导致应用程序停止 这是代码MainActivity

public class MainActivity extends Activity {

    ListView lv;
    String[] items;
    Button btnA1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btnA1 = (Button) findViewById(R.id.btnA);
        btnA1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent a1 = new Intent(getApplicationContext(), Player.class);
                startActivity(a1);
                finish();
            }
        });
        lv = (ListView) findViewById(R.id.lvPlaylist);
        final ArrayList<File> mySongs = findSongs(Environment.getExternalStorageDirectory());
        items = new String[mySongs.size()];
        for (int i = 0; i < mySongs.size(); i++) {
            items[i] = mySongs.get(i).getName().toString().replace(".mp3", "").replace(".wav", "");
        }

        ArrayAdapter<String> adp = new ArrayAdapter<String>(getApplicationContext(), R.layout.song_layout,
                R.id.textView, items);
        lv.setAdapter(adp);
        lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
                startActivity(new Intent(getApplicationContext(), Player.class).putExtra("pos", position)
                        .putExtra("songlist", mySongs));
            }
        });
    }

    public ArrayList<File> findSongs(File root) {
        ArrayList<File> al = new ArrayList<File>();
        File[] files = root.listFiles();
        for (File singleFile : files) {
            if (singleFile.isDirectory() && !singleFile.isHidden()) {
                al.addAll(findSongs(singleFile));
            } else {
                if (singleFile.getName().endsWith(".mp3") || singleFile.getName().endsWith(".wav")) {
                    al.add(singleFile);
                }
            }
        }
        return al;
    }

    @Override
    public void onBackPressed() {
        AlertDialog.Builder ab = new AlertDialog.Builder(MainActivity.this);
        ab.setTitle("Exit");
        ab.setMessage("Are You Sure Exit?");
        ab.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
                android.os.Process.killProcess(android.os.Process.myPid());
                System.exit(1);
                MainActivity.this.finish();
            }
        });

        ab.setNegativeButton("No", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
            }
        });
        ab.show();
    }
}

错误在于

public ArrayList<File> findSongs(File root) {
    ArrayList<File> al = new ArrayList<File>();
    File[] files = root.listFiles();
    for (File singleFile : files) {
        if (singleFile.isDirectory() && !singleFile.isHidden()) {
            al.addAll(findSongs(singleFile));
        } else {
            if (singleFile.getName().endsWith(".mp3") || singleFile.getName().endsWith(".wav")) {
                al.add(singleFile);
            }
        }
    }
    return al;
} 

如果我替换if (singleFile.isDirectory() && !singleFile.isHidden()) { al.addAll(findSongs(singleFile)); 到if (singleFile.isDirectory() && singleFile.isHidden()) { al.addAll(findSongs(singleFile));那么应用程序只会加载sdcard上的mp3文件，因为sdcard / music不会

如果我很恐怖在singleFile中，应用程序将被停止