MVC 弹出提示框

第一种弹框成功后要刷新界面

[HttpPost]
        public ActionResult Add(Maticsoft.Model.Project.ProjectMoneyPlan model)
        {
            model.Money = new Maticsoft.Model.Struct.DRMB(model.Money).ToDouble().ToString();
            Maticsoft.BLL.User.LoginUser login = new Maticsoft.BLL.User.LoginUser();
            model.Creater = login.Email;
            try
            {
                if (bll.Exist("Pro_MoneyPlan", "where ProCode='" + model.ProCode + "' ", "ProCode") && bll.Exist("Pro_MoneyPlan", "where Year=" + model.Year , "Year") && bll.Exist("Pro_MoneyPlan", "where Month=" + model.Month, "Month"))
                {
                    ///弹框
                   string script = String.Format("<script>alert('数据已经存在！');location.href='{0}'</script>",  Url.Action("Add"));
                   return Content(script ,"Text/html");
                }
                else
                {
                    bll.Add(model);
                    return View("List");
                }
            }
            catch (Exception ex)
            {
                return new Maticsoft.BLL.Error().DoError(ex);
            }
        }   

第二种弹框成功后不刷新界面：

[HttpPost]
        public ActionResult Add(Maticsoft.Model.Project.ProjectMoneyPlan model)
        {
            model.Money = new Maticsoft.Model.Struct.DRMB(model.Money).ToDouble().ToString();
            Maticsoft.BLL.User.LoginUser login = new Maticsoft.BLL.User.LoginUser();
            model.Creater = login.Email;
            try
            {
                if (bll.Exist("Pro_MoneyPlan", "where ProCode='" + model.ProCode + "' ", "ProCode") && bll.Exist("Pro_MoneyPlan", "where Year=" + model.Year , "Year") && bll.Exist("Pro_MoneyPlan", "where Month=" + model.Month, "Month"))
                {
                   ViewData["ProName"] = SelecOpption.GetOpption("PRO_B", "", "Code,Name");//获取项目名称
                   ViewData["Year"] = GetYear();
                   ViewData["Month"] = GetMonth();
                   ///弹框
                   ViewBag.isExist = false;
                   return View();
                }
                else
                {
                    bll.Add(model);
                    return View("List");
                }
            }
            catch (Exception ex)
            {
                return new Maticsoft.BLL.Error().DoError(ex);
            }
        }   

前台：

@if (ViewBag.isExist == false)
{
    <script type="text/javascript">
        alert("您要添加的数据已经存在！")
    </script>
}