MVC4 下DropDownList使用方法

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace SupermarketManagement.Controllers
{
    public class HtmlControlsController : Controller
    {
        //单位枚举
        public enum Units
        {
            米,
            厘米,
            毫米,
            微米
        }

        /// <summary>
        /// DropDownList 控件
        /// </summary>
        /// <returns></returns>
        public ActionResult DropDownListIndex()
        {
            //1、第一种表现形式(性别)
            List<SelectListItem> sexItems = new List<SelectListItem>();
            sexItems.Add(new SelectListItem { Text = "请选择", Value = "0", Selected = true });
            sexItems.Add(new SelectListItem { Text = "男", Value = "1" });
            sexItems.Add(new SelectListItem { Text = "女", Value = "2" });
            ViewBag.Sex = sexItems;


            //2、第二种表现形式
              var values = Enum.GetValues(typeof(Units)).Cast<Units>();
            var items = from value in values
                        select new SelectListItem { Text = value.ToString(),Value=value.ToString() };
            ViewBag.Unit = items;//2.1

            ViewBag.UnitEx = Units.米.ToSelectListItem("毫米");//2.2：这里用的扩展方法


            //3、第三种表现形式选中(用户更新，展示)
            List<SelectListItem> list = new List<SelectListItem>()
            {
                new SelectListItem(){Value="Man",Text="Man"},
                new SelectListItem(){Value="Female",Text="Female"}
            };
            ViewBag.Gender = new SelectList(list, "Value", "Text","Female");

            return View();
        }
    }

    //枚举扩展方法
    public static class ExSelectListItem
    {
        /// <summary>
        /// 显示所有列表
        /// </summary>
        /// <param name="valueEnum"></param>
        /// <returns></returns>
        public static IEnumerable<SelectListItem> ToSelectListItem(this Enum valueEnum)
        {
            var values = Enum.GetValues(valueEnum.GetType());
            var result = from int value in values select new SelectListItem { Text = Enum.GetName(valueEnum.GetType(), value), Value = value.ToString() };
            return result;
        }

        /// <summary>
        /// 选中的列表项
        /// </summary>
        /// <param name="valueEnum"></param>
        /// <param name="selectName"></param>
        /// <returns></returns>
        public static List<SelectListItem> ToSelectListItem(this Enum valueEnum, string selectName)
        {
            return (from int value in Enum.GetValues(valueEnum.GetType())
                    select new SelectListItem
                           {
                               Text = Enum.GetName(valueEnum.GetType(), value),
                               Value = Enum.GetName(valueEnum.GetType(), value),
                               Selected = Enum.GetName(valueEnum.GetType(), value) == selectName ? true : false
                           }).ToList();
        }
    }
}