//后台 
    public ActionResult OrderAdd()        {            var items = new List<SelectListItem>()            {              (new SelectListItem(){Text = "男", Value = http://www.mamicode.com/"Male"}),              (new SelectListItem(){Text = "女", Value = http://www.mamicode.com/"female"})            };            ViewBag.sexList = items;            return View();        }

//前端//默认为空@Html.DropDownList("sexList", ViewBag.sexList as  List<SelectListItem>,"")//默认为第一个值，也就是 "男"@Html.DropDownList("sexList", ViewBag.sexList as List<SelectListItem>)