<ul class="nav navbar-nav navbar-right">                        
                            <li class="">
                                <a href="javascript:;" rel="external nofollow"  class="user-profile dropdown-toggle" data-toggle="dropdown" aria-expanded="false">
                                    <img src="@Url.Content("~/assets/img/user2.png")" alt="">@CPU.UserProfile.User.UserID
                                    <span class="fa fa-angle-down"></span>
                                </a>
                                <ul class="dropdown-menu dropdown-usermenu pull-right" style="width:35px">
                                    <li>
                                        @using (Html.BeginForm("LogOff", "Account", FormMethod.Post, new { id = "logoutForm", style = "padding: 12px 0px;" }))
                                        {
                                            @Html.AntiForgeryToken()
                                            <a href="javascript:document.getElementById('logoutForm').submit()" rel="external nofollow" ><i class="fa fa-sign-out pull-right"></i> Log Out</a>
                                        }
                                    </li>
                                </ul>
                            </li>
                            <li class="hidden-xs"><a><span>在線人數(shù): @System.Web.HttpContext.Current.Application["OnLineUserCount"] 人</span></a></li>                            
                        </ul>

[HttpPost]
        [AllowAnonymous]
        [ValidateAntiForgeryToken]
        public ActionResult LogOff()
        {
            FormsAuthentication.SignOut();//退出登錄
            System.Web.HttpContext.Current.Session.Abandon();//清理緩存
            return RedirectToAction("Login", "Account");
        }