private void Window_Loaded(object sender, RoutedEventArgs e)
{
ProductCatalog prodCat = new ProductCatalog();
_dsProdCat = prodCat.GetProductInfo();
this.DataContext = _dsProdCat.Tables["Category"];
_order = new Order();
_employee = new Employee();
this.orderListView.ItemsSource = _order.OrderItemList;
}