private void btnDelete_Click(object sender, RoutedEventArgs e)
        {
            var selectBook = dgMain.SelectedItem as Book;

            if (selectBook != null)
            {
                service.DeleteBook(selectBook);
                dgMain.ItemsSource = service.GetBooks();
            }
        }
 private void DeleteBookExecute()
 {
     _service.DeleteBook(DeleteBook);
     DeleteBook = null;
     Books      = null;
 }