void SizeChanged(object sender, ItemSizeChangedEventArgs e)
 {
     RaisePropertyChanged("Size");
     if (Size.DisplaySize != FileSystemItemSize.Calculating)
     {
         UpdateAffectsTotalSize();
     }
 }
 void TotalSize_SizeChanged(object sender, ItemSizeChangedEventArgs e)
 {
     TotalSize = new FileSystemItemSize(e.Size.NumSize);
 }