public ActionResult Login(FormCollection f)
        {
            NguoiDungDAO tk   = new NguoiDungDAO();
            string       user = f["user"].ToString();
            string       pass = f["password"].ToString();

            if (tk.Login(user, pass))
            {
                var nguoidung = tk.GetNguoiDungById(user);
                Session["taikhoan"] = nguoidung;
                return(RedirectToAction("Index", "NguoiDung"));
            }
            return(RedirectToAction("Index", "Home"));
        }