public object Convert(object value, Type targetType, object parameter, string language)
 {
     //var image = value as Image;
     //if (image == null || image.BaseUri == null)
     //{
     //    var bitmap = new BitmapImage(new Uri("ms-appx:///Assets/www/news_detail_header_def.jpg"));
     //    var notifier = new TaskCompletionNotifier<BitmapImage>();
     //    notifier.SetTask(Task.FromResult(bitmap));
     //    return notifier;
     //}
     //else
     //{
     //    var task = Task.Run(async () =>
     //    {
     //        var cache = ServiceLocator.Current.GetInstance<ImageCache>();
     //        var uri = await cache.GetImageSourceFromUrlAsync(image.BaseUri.ToString());
     //        return uri;
     //    });
     //    var notifier = new TaskCompletionNotifier<BitmapImage>();
     //    notifier.SetTask(task, c => new BitmapImage(c));
     //    return notifier;
     //}
     if (value != null)
     {
         var task = Task.Run(async() =>
         {
             var cache = ImageCache.CreateInstance();
             var uri   = await cache.GetImageSourceFromUrlAsync(value.ToString());
             return(uri);
         });
         var notifier = new TaskCompletionNotifier <BitmapImage>();
         notifier.SetTask(task, c => new BitmapImage(c));
         return(notifier);
     }
     else
     {
         return(string.Empty);
     }
 }