private void PlayMedia(string pointUrl = null)
        {
            this.PlayBtn.Text = "停止";


            WMPLib.IWMPPlaylist playlist = _player.playlistCollection.newPlaylist("myplaylist");

            _player.PlayStateChange +=
                new WMPLib._WMPOCXEvents_PlayStateChangeEventHandler(Player_PlayStateChange);
            _player.MediaError +=
                new WMPLib._WMPOCXEvents_MediaErrorEventHandler(Player_MediaError);
            _player.CurrentItemChange += new WMPLib._WMPOCXEvents_CurrentItemChangeEventHandler(player_CurrentItemChange);

            playlist.clear();

            if (string.IsNullOrWhiteSpace(pointUrl) == false)
            {
                media = _player.newMedia(pointUrl);
                playlist.appendItem(media);
            }

            var array = Shuffle <string>(_listUrl.ToArray());

            foreach (string urlStr in array)
            {
                media = _player.newMedia(urlStr);
                playlist.appendItem(media);
            }
            _player.currentPlaylist = playlist;

            _timer.Start();
            _player.controls.play();
        }