void stopPlayback()
        {
            if (_player == null)
            {
                return;
            }

            _player.Stop();
            _player = null;
            _playBackButton.SetTitle("Playback", UIControlState.Normal);
        }
 void _playBackButton_TouchDown(object sender, EventArgs e)
 {
     if (_player == null && _recorder == null)
     {
         _player = new AudioQueuePlayer(_url);
         _player.Play();
         _playBackButton.SetTitle("Stop", UIControlState.Normal);
     }
     else
     {
         stopPlayback();
     }         
 }        
 void _playBackButton_TouchDown(object sender, EventArgs e)
 {
     if (_player == null && _recorder == null)
     {
         _player = new AudioQueuePlayer(_url);
         _player.Play();
         _playBackButton.SetTitle("Stop", UIControlState.Normal);
     }
     else
     {
         stopPlayback();
     }
 }
        void stopPlayback()
        {
            if (_player == null) return;

            _player.Stop();
            _player = null;
            _playBackButton.SetTitle("Playback", UIControlState.Normal);
        }