//this method gets called to add items in the invoice public void Bill(string itemName) { Invoice invoice = new Invoice(new InvoiceIndustry().createInvoiceType(itemName)); Session["selectedItem"] = itemName; invoice.AddFood((List <Item>)Session["items"]); invoice.ChargeInItem(Get_Service(), (List <Item>)Session["items"], itemName); Custom_GridView(itemName); }