.net mvc DropDownList 下拉框_无限级分类

2、Controller：

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

namespace MvcTest.Controllers
{
    [ValidateInput(false)]
    public class HomeController : Controller
    {
        private testEntities db = new testEntities();

        [LoginFilter]
        public ActionResult Index()
        {
            BindDropDownList();
            return View();
        }

        //绑定顶级分类       
        private void BindDropDownList()
        {
            List<SelectListItem> select1 = new List<SelectListItem>();
            var one = from c in db.Categories where c.pId == 0 select c;
            foreach (var b in one)
            {
                string name = b.name; string id = b.id.ToString();
                select1.Add(new SelectListItem
                {
                    Text = "> " + name,
                    Value = id
                });
                int sonparentpid = int.Parse(id);
                string blank = "　┠ ";
                //递归子分类方法
                BindNode(sonparentid, blank, select1);
            }
            ViewBag.caList = new SelectList(select1, "Value", "Text");
        }

        //绑定子分类      
        private void BindNode(int pid, string blank, List<SelectListItem> select1)
        {
            var two = db.Categories.Where(c => c.pId == pid);
            foreach (var c in two)
            {
                string zname = blank + c.name;
                string zid = c.id.ToString();
                select1.Add(new SelectListItem
                {
                    Text = zname,
                    Value = zid
                });
                int sonparentid = int.Parse(zid);
                string blank2 = blank + "━";
                BindNode(sonparentid, blank2, select1);
            }
        }
    }
}

@Html.DropDownListFor(a => a.caId, ViewBag.caList as IEnumerable<SelectListItem>,"---请选择---" , new { style = "width: 120px;" })