private void ddlAmount_SelectedIndexChanged(object sender, EventArgs e) { DropDownList selectedList = (DropDownList)sender; int quantity = Convert.ToInt32(selectedList.SelectedValue); int cartId = Convert.ToInt32(selectedList.ID); PurchaseModel model = new PurchaseModel(); model.UpdateQuantity(cartId, quantity); Response.Redirect("~/Pages/ShoppingCart.aspx"); }