protected override void RaiseAllCanExecuteChanged()
 {
     base.RaiseAllCanExecuteChanged();
     ImportAttachmentFromDiskCommand.RaiseCanExecuteChanged();
     ImportAttachmentFromClipboardCommand.RaiseCanExecuteChanged();
     SaveAttachmentToDiskCommand.RaiseCanExecuteChanged();
     OpenAttachmentCommand.RaiseCanExecuteChanged();
     DeleteAttachmentCommand.RaiseCanExecuteChanged();
 }