public ActionResult ThemVaoGioHang(int?masanpham)
        {
            if (Session["GioHangTamThoi"] == null)
            {
                Session["GioHangTamThoi"] = new List <ClassGioHangTamThoi>();
                Session["Dem"]            = "Trống";
            }
            List <ClassGioHangTamThoi> GioHangTamThoi = Session["GioHangTamThoi"] as List <ClassGioHangTamThoi>;

            if (GioHangTamThoi.FirstOrDefault(n => n.MaSanPham == masanpham) == null)
            {
                tbSanPham sanpham = dt.tbSanPhams.Find(masanpham);
                if (Session["Dem"].ToString() == "Trống")
                {
                    Session["Dem"] = "0";
                }
                Session["Dem"] = Int32.Parse(Session["Dem"].ToString()) + 1;
                ClassGioHangTamThoi item = new ClassGioHangTamThoi()
                {
                    MaSanPham  = sanpham.MaSanPham,
                    TenSanPham = sanpham.TenSanPham,
                    SoLuong    = 1,
                    GiaSanPham = decimal.ToInt32(sanpham.GiaSanPham.Value)
                };
                GioHangTamThoi.Add(item);
            }
            else
            {
                ClassGioHangTamThoi gio = GioHangTamThoi.FirstOrDefault(n => n.MaSanPham == masanpham);
                gio.SoLuong++;
            }
            return(Redirect(Request.UrlReferrer.ToString()));
        }
        public ActionResult CapNhat(int masanpham, int soluongmoi)
        {
            List <ClassGioHangTamThoi> giohangtamthoi = Session["GioHangTamThoi"] as List <ClassGioHangTamThoi>;
            ClassGioHangTamThoi        capnhat        = giohangtamthoi.FirstOrDefault(n => n.MaSanPham == masanpham);

            if (capnhat != null)
            {
                capnhat.SoLuong = soluongmoi;
            }
            return(Redirect(Request.UrlReferrer.ToString()));
        }