Html.DropDownList 选中 mvc view 弱类型

List<Model.SysGroup> listGroup = sysGroupBll.Where(o => o.IsSb == true, o => o.Id).ToList();
            List<SelectListItem> items = new List<SelectListItem>();
            foreach (var group in listGroup)
            {
                items.Add(new SelectListItem { Text = group.Name, Value = group.Id });
            }
            this.ViewData["list"] = items;
            this.ViewData["GroupId"] = CurrentUser.SysGroup.FirstOrDefault().Id;

<td>组 @Html.DropDownList("GroupId", ViewData["list"] as IEnumerable<SelectListItem>)</td>