private void BtnUpdateBook_Click(object sender, RoutedEventArgs e)
        {
            if (!Validation())
            {
                return;
            }
            Book newBook = new Book
            {
                Id       = bk.Id,
                Name     = tbBookName.Text,
                Author   = tbAuthorName.Text,
                CountNow = Convert.ToInt32(tbBookCount.Text),
                Count    = (Convert.ToInt32(tbBookCount.Text) - bk.CountNow) + bk.Count,
                Price    = Convert.ToDecimal(tbPrice.Text)
            };

            dr.UpdateBooks(newBook);
            btnAddBook.Visibility    = Visibility.Visible;
            btnUpdateBook.Visibility = Visibility.Hidden;
            btnDeleteBook.Visibility = Visibility.Hidden;
            ResetTextBox();
            FillDG();
        }