中国省市地区三级联动

public class HomeController : Controller
    {
        //
        // GET: /Home/

        //默认显示的主页面
        public ActionResult Index()
        {
            List<ChinaStates> listS = new ChinaStatesBF().SelectSheng();
            SelectList listSheng = new SelectList(listS,"AreaCode","AreaName","0001");

            List<ChinaStates> listC = new ChinaStatesBF().SelectCheng("11");
            SelectList listCity = new SelectList(listC, "AreaCode", "AreaName");
            ViewBag.Citys = listCity;

            List<ChinaStates> listD = new ChinaStatesBF().SelectDiQu("1101");
            SelectList listDiQu = new SelectList(listD, "AreaCode", "AreaName");
            ViewBag.DiQus = listDiQu;


            return View(listSheng);
        }

        [HttpPost]
        public ActionResult Index(string shengcode,string shicode,string diqucode)
        {
            try
            {
                //按提交的省编号定位省份
                List<ChinaStates> listS = new ChinaStatesBF().SelectSheng();
                SelectList listSheng = new SelectList(listS, "AreaCode", "AreaName", shengcode);

                //按省份查询城市
                List<ChinaStates> listC = new ChinaStatesBF().SelectCheng(shengcode);
                SelectList listCity = new SelectList(listC, "AreaCode", "AreaName", shicode);                
                ViewBag.Citys = listCity;

                //判断是否更改城市，来查询地区
                var b = listC.Exists(p => p.AreaCode == shicode) ? shicode : listC[0].AreaCode;
                List<ChinaStates> listD = new ChinaStatesBF().SelectDiQu(b);
                SelectList listDiQu = new SelectList(listD, "AreaCode", "AreaName", diqucode);                
                ViewBag.DiQus = listDiQu;
                return View(listSheng);
            }
            catch
            {
                return RedirectToAction("Index");
            }           
        }
    }

 public class ChinaStatesBF
    {
        private MyDbDataContext Context = new MyDbDataContext();
        //查询省
        public List<ChinaStates> SelectSheng()
        {
            var q = Context.ChinaStates.Where(p => p.ParentAreaCode == "0001");
            if (q.Count()>0)
            {
                return q.ToList();
            }
            return null;
        }

        //查市
        public List<ChinaStates> SelectCheng(string parentAreaCode)
        {
            var q = Context.ChinaStates.Where(p=>p.ParentAreaCode==parentAreaCode);
            if (q.Count()>0)
            {
                return q.ToList();
            }
            return null;
        }
        //查地区
        public List<ChinaStates> SelectDiQu(string parentAreaCode)
        {
            var q = Context.ChinaStates.Where(p => p.ParentAreaCode == parentAreaCode);
            if (q.Count() > 0)
            {
                return q.ToList();
            }
            return null;
        }
    }

<div>
        @using (@Html.BeginForm("Index", "Home", FormMethod.Post))
        {
            @Html.Label("text", "省份")    
            @Html.DropDownList("shengcode", Model, new { onchange="document.forms[0].submit()" })
            @Html.Label("text", "城市")    
            @Html.DropDownList("shicode",ViewBag.Citys as SelectList, new { onchange="document.forms[0].submit()" })
            @Html.Label("text", "地区")    
            @Html.DropDownList("diqucode", ViewBag.DiQus as SelectList, new { onchange="document.forms[0].submit()" })
        }
    </div>

效果