private void DownloadItemsInternal(Func <DownloadItem, bool> canDownload)
 {
     for (int i = 0; i < DownloadingImages.Count; i++)
     {
         var item = DownloadingImages[i];
         if (canDownload(item))
         {
             DownloadingImages.Remove(item);
             i--;
         }
     }
 }
 public void DeleteDownload(DownloadItem item)
 {
     DownloadingImages.Remove(item);
 }