如何在 Android 上使用 ContentResolver.Query 从 SdCard 获取 mp3 文件列表？

Question

我在 mnt/sdcard 中创建了一个名为 Cuzler 的文件夹，并放置了一些 mp3 文件..这里是我正在使用的代码..

File cuzFolder = new File(Environment.getExternalStorageDirectory() + "/Cuzler/");
String storageFolder = cuzFolder.getPath(); 

Uri urlCuz = Uri.parse(storageFolder); 
Log.i(TAG, "CUZ: " + urlCuz.toString());
Cursor cur = mContentResolver.query(urlCuz, null,

MediaStore.Audio.Media.IS_MUSIC + " = 1", null, null);
Log.i(TAG, "Query finished. " + (cur == null ? "Returned NULL." : "Returned a cursor."));

cur 返回 null.. 我已授予写/读权限。我正在制作一个 mp3 播放器，它将在 sdcard 的一个文件夹中播放一些 mp3，路径是正确的，因为我正在将 mp3 下载到这个文件夹并且没有问题。但我不明白为什么查询返回 null ？

我也尝试过类似的东西

Uri urlCuz = Uri.parse("content://" + storageFolder); 

并提供直接链接，如 mnt/sdcard/Cuzler 或 /mnt/scard/Cuzler

我该如何解决这个问题？

Answer 1

public class MainActivity extends AppCompatActivity {

    ListView listView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.list_view);

        ContentResolver resolver = MainActivity.this.getContentResolver();
        ArrayList<String> stringArrayList = new ArrayList<String>();


        String GENRE_ID      = MediaStore.Audio.Genres._ID;
        String GENRE_NAME    = MediaStore.Audio.Genres.NAME;
        String SONG_ID       = android.provider.MediaStore.Audio.Media._ID;
        String SONG_TITLE    = android.provider.MediaStore.Audio.Media.TITLE;
        String SONG_ARTIST   = android.provider.MediaStore.Audio.Media.ARTIST;
        String SONG_ALBUM    = android.provider.MediaStore.Audio.Media.ALBUM;
        String SONG_YEAR     = android.provider.MediaStore.Audio.Media.YEAR;
        String SONG_TRACK_NO = android.provider.MediaStore.Audio.Media.TRACK;
        String SONG_FILEPATH = android.provider.MediaStore.Audio.Media.DATA;
        String SONG_DURATION = android.provider.MediaStore.Audio.Media.DURATION;


        String[] genreColumns = {
               SONG_ID,
                SONG_TITLE
        };

        if (checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {

            // Should we show an explanation?
            if (shouldShowRequestPermissionRationale(
                    Manifest.permission.READ_EXTERNAL_STORAGE)) {
                // Explain to the user why we need to read the contacts
            }

            requestPermissions(new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                    1);

            // MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE is an
            // app-defined int constant that should be quite unique

            return;
        }

        Cursor cursor = resolver.query(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,genreColumns,null,null,null);
        for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext())
//            genreIdToGenreNameMap.put(cursor.getString(0), cursor.getString(1));
             stringArrayList.add(cursor.getString(1));

        cursor.close();

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,stringArrayList);
        listView.setAdapter(adapter);

    }
}