procedure TMainForm.ShellListThumbnailUpdated(sender: TObject; item: TListItem;
   var ThumbnailBitmap: TBitmap);
 var lBitmap: TBitmap;
 begin
   //Create or load a custom bitmap in the correct size.
   lBitmap := GetCustomBitmap(TJamCheckableListItem(item), ThumbnailBitmap.Height, ThumbnailBitmap.Width);
   ThumbnailBitmap.Assign(lBitmap);
   FreeAndNil(lBitmap); //avoid memory leak.
 end;