private void Delete(object sender, RoutedEventArgs e) { if (_book.IsBorrowed) { BookError.Content = "A könyv nem törölhető mert ki van kölcsönözve!"; BookError.Visibility = Visibility.Visible; } else { try { BookError.Visibility = Visibility.Collapsed; BookDataProvider.DeleteById(_book.Id); DialogResult = true; Close(); } catch (Exception ex) { log.Error(ex.Message); } } }