关于指定页跳转到登陆，登陆后再跳到指定页的方法

        public ActionResult Index()
        {
            if (!SignHelp.IsSign()) return ChangeResult();         
            return View();
        }


//跳到login页
        public ActionResult ChangeResult()
        {
            var returnurl = HttpUtility.UrlEncode("/visitPage/index");
            return Redirect("/login/index?returnUrl=" + returnurl);
        }

        public ActionResult Index()
        {
            string returnurl = Request.QueryString["returnUrl"];
            returnurl = HttpUtility.UrlDecode(returnurl);
            ViewBag.ReturnUrl = returnurl;
            return View();
        }

 <input type="hidden" id="returnurl" value="@ViewBag.ReturnUrl" />

 var returnurl = $("#returnurl").val();          
 location.replace(returnurl == "" ? "/home/index" : returnurl);