mvc3.0 中dropdownlist的使用

0. 普通的下拉框
@Html.DropDownList("type", DataHelper.GetOrderStatus(null, "--全部订单--"), new { @style = "160px" })

　　1. typeof(Gender) 利用的枚举。

@model SearchEView
@Html.EnumDropdown(Model, m => m.Gender, null, typeof(Gender))

　　2.ajax的dropdown请求。

@Html.Hidden("trainId", 0)
        @Html.AjaxDropdown("ClassId", null, "AuthorClass", "GetItems", "trainId", new { }, "search")

在搜索search中，ajax的dropdown控件名称都是以search.为前缀的，在搜索的时候用searchView 能传过去值。
"ClassId" 是获取的值，null 是传值参数，authorclass 是control，getItems是action，trainId是搜索参数

带三个参数的获取dropdownlist值的方法

类 型：<br />
        @Html.EditorFor(m=>m.Setting)
        @Html.ValidationMessageFor(m=>m.Setting)
@Html.Hidden("Refresh","")
@Html.AjaxDropdown("ParentId", null, "AuthorClass", "GetItems", "Refresh", new { @class = "def" }, null, Setting => "TrainId")

 public override ActionResult GetItems(int? key, int? search,int? trainId)
         {
             key = key ?? 0;
             trainId = trainId ?? search;
             if (key != 0)
             {
                 trainId=service.GetById(key).Setting;

             }
             if (trainId == null&&key==0)
             {
                 trainId = -1;
             }
             var models = service.GetAll().Where(m => m.Setting == trainId);
             var tree = new ClassTree<IClassModel>(models);
            if (trainId.HasValue)
            {
                tree = tree.Format(new AuthorClass { ClassName = "全部" });
            }

            var treeModels = tree.Select(m =>
                new SelectListItem
                {
                    Text = Server.HtmlEncode(m.ClassName),
                    Value = m.ClassId == 0 ? "" : m.ClassId.ToString(),
                    Selected = (m.ClassId == key)
                }).ToList();
             
             return Json(models==null?null:treeModels);
         }