IEnumerable<IVirtualItem> IVirtualFolder.EnumerateItems(VirtualItemTypes type)
 {
     if (type.HasFlag(VirtualItemTypes.Folder))
         return imageFolders;
     else
         return null;
 }
 IEnumerable<IVirtualItem> IVirtualFolder.EnumerateItems(VirtualItemTypes type)
 {
     #if false
     // The following code is to test the VirtualFolderListView.
     if (type.HasFlag(VirtualItemTypes.NonFolder))
     {
         foreach (var file in files)
         {
             yield return file;
             System.Threading.Thread.Sleep(500);
         }
     }
     #else
     if (type.HasFlag(VirtualItemTypes.NonFolder))
         return files;
     else
         return null;
     #endif
 }