private void BtnDeleteBook_Click(object sender, RoutedEventArgs e)
 {
     if (!Validation())
     {
         return;
     }
     if (MessageBox.Show("Do you want to delete this book?", "Question", MessageBoxButton.YesNo, MessageBoxImage.Information) == MessageBoxResult.Yes)
     {
         dr.DeleteBooks(bk.Id);
         btnAddBook.Visibility    = Visibility.Visible;
         btnUpdateBook.Visibility = Visibility.Hidden;
         btnDeleteBook.Visibility = Visibility.Hidden;
         FillDG();
         ResetTextBox();
     }
 }