public void PlayPause()
 {
     if (MediaControllingViewModel.IsPlaying)
     {
         MediaControllingViewModel.Pause();
     }
     else
     {
         MediaControllingViewModel.Play();
     }
 }
        public async Task ChangeSourceAsync(StorageFile file)
        {
            if (file != null)
            {
                Source = MediaSource.CreateFromStorageFile(file);
                MediaControllingViewModel.ChangeMediaPlayerSource(Source);
                CurrentStorageFile = file;
                await VideoPropsViewModel.UpdateVideoPropsByStorageFile(file);

                ParentVm.RefreshTitle();
                ViewModelLocator.Current.TeachingTipsViewModel.StartIfAppropriate(3);
            }
        }