Java 未知URL:content://media/external/audio/media/null?

我正在创建一个mp3player，其中所有音频文件都从本地设备存储器中获取。我在列表视图中显示项目

但当我点击任何特定的项目时，我遇到了一个例外。我无法解决这个问题

Unknown URL: content://media/external/audio/media/null

这是我的密码-

public class MainActivity extends AppCompatActivity {
      MediaPlayer mediaPlayer;
       private long lg;
       private Context mContext;
       private android.app.Activity mActivity;
        private ArrayList<Song> songList;
          private MediaPlayer mPlayer;

        private java.util.HashMap<Long,String> mAudioMap = new java.util.HashMap<>();

        private ListView songView;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            runtimpermission();
             mContext = getApplicationContext();
        mActivity= MainActivity.this;
            songView = (ListView) findViewById(R.id.song_list);
            songList = new ArrayList<Song>();
            SongAdapter songAdt = new SongAdapter(this, songList);
            songView.setAdapter(songAdt);
            getSongList();
            Collections.sort(songList, new Comparator<Song>() {
                public int compare(Song a, Song b) {
                    return a.getTitle().compareTo(b.getTitle());
                }
            });

            songView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

                @Override
                public void onItemClick(AdapterView<?>  adapterView, View view, int position, long id) {
                    String titleValue = (String) adapterView.getItemAtPosition(position);


                      Uri fileUri =Uri.withAppendedPath(android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,   titleValue);
                        stopPlaying();

                        try{
                            // Initialize the media player
                            mPlayer = new MediaPlayer();
                            mPlayer.setAudioStreamType(android.media.AudioManager.STREAM_MUSIC);


                            // Set media player data source
                            mPlayer.setDataSource(mContext,fileUri );
                            //Toast.makeText(mContext,contentUri+"",Toast.LENGTH_SHORT).show();

                            // Prepare the selected audio
                            mPlayer.prepare();

                            // Finally, start playing selected music
                            mPlayer.start();

                            // Listener for media player completion
                            mPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                                @Override
                                public void onCompletion(MediaPlayer mediaPlayer) {

                                }
                            });


                        }catch (java.io.IOException e){
                            // When IO exception catch
                            e.printStackTrace();
                            Toast.makeText(mContext,"Error.",Toast.LENGTH_SHORT).show();
                        }

                }
            });

        }


        public void getSongList() {
            //retrieve song info
            ContentResolver musicResolver = getContentResolver();
            Uri musicUri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
            Cursor musicCursor = musicResolver.query(musicUri, null, null, null, null);

            if(musicCursor!=null && musicCursor.moveToFirst()){
                //get columns
                int titleColumn = musicCursor.getColumnIndex
                        (android.provider.MediaStore.Audio.Media.TITLE);
                int idColumn = musicCursor.getColumnIndex
                        (android.provider.MediaStore.Audio.Media._ID);
                int artistColumn = musicCursor.getColumnIndex
                        (android.provider.MediaStore.Audio.Media.ARTIST);

                //add songs to list
                do {
                    long thisId = musicCursor.getLong(idColumn);
                    String thisTitle = musicCursor.getString(titleColumn);
                    String thisArtist = musicCursor.getString(artistColumn);
                    songList.add(new Song(thisId, thisTitle, thisArtist));
                }
                while (musicCursor.moveToNext());
            }

        }
protected void stopPlaying(){
        if(mPlayer!=null){
            mPlayer.stop();
            mPlayer.release();
            mPlayer = null;
            Toast.makeText(this,"Stop playing",Toast.LENGTH_SHORT).show();

        }
        }

    }

 E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.monstertechno.musicplayerappui, PID: 12872
                  java.lang.IllegalStateException: Unknown URL: content://media/external/audio/media/null
                      at android.os.Parcel.readException(Parcel.java:1607)
                      at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:235)
                      at android.database.DatabaseUtils.readExceptionWithFileNotFoundExceptionFromParcel(DatabaseUtils.java:187)
                      at android.content.ContentProviderProxy.openTypedAssetFile(ContentProviderNative.java:692)
                      at android.content.ContentResolver.openTypedAssetFileDescriptor(ContentResolver.java:1104)
                      at android.content.ContentResolver.openAssetFileDescriptor(ContentResolver.java:942)
                      at android.content.ContentResolver.openAssetFileDescriptor(ContentResolver.java:865)
                      at android.media.MediaPlayer.setDataSource(MediaPlayer.java:1007)
                      at android.media.MediaPlayer.setDataSource(MediaPlayer.java:973)
                      at com.monstertechno.musicplayerappui.MainActivity$2.onItemClick(MainActivity.java:82)
                      at android.widget.AdapterView.performItemClick(AdapterView.java:310)
                      at android.widget.AbsListView.performItemClick(AbsListView.java:1146)
                      at android.widget.AbsListView$PerformClick.run(AbsListView.java:3050)
                      at android.widget.AbsListView$3.run(AbsListView.java:3893)
                      at android.os.Handler.handleCallback(Handler.java:739)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:148)