public async Task Play(Song a, MediaElement m)
        {
            if (Songs.Count != 0)
            {
                if (Songs.Contains(a))
                {
                    NowIndex = Songs.IndexOf(a);
                }
                else
                {
                    Songs.Add(a);
                    NowIndex = Songs.IndexOf(a);
                }
            }
            else
            {
                Songs.Add(a);
                NowIndex = 0;
            }
            await Task.Run(() =>
            {
                a.PlayOnce();
            });

            var stream = await a.AudioFile.OpenAsync(Windows.Storage.FileAccessMode.Read);
            m.SetSource(stream, a.AudioFile.ContentType);
            OnNotifyPlayBackEvent(a);
        }