asp.net MVC中dropdownlist的使用(并设置选中项)

后台代码：

  public ActionResult Index(FormCollection collection)
          {
              IList<Project> li = Utility.SqlHelper.getProjectList();
              SelectList selec = new SelectList(li, "ID", "Name");
      
              if (collection["drop"] != null)
              {
                  string projectID = collection["drop"];
                  selec = new SelectList(li, "ID", "Name", projectID);//根据返回的选中项值设置选中项   
               ViewData["ruturned"] = collection["drop"];
              }
              ViewData["drop"] = selec;
            return View();
        }

前端代码：
  @using (Html.BeginForm()){
@Html.DropDownList("drop", ViewData["d"] as SelectList)
    <input  type="submit" value="查看对应分组列表" />
        }
        <p> 当前项目ID： @ViewData["ruturned"]</p>