三级列表

<Script>
 function GetCityByParentID() {
        $("#City").empty();
        $.ajax({
            url: '/Doctor/ChangeCity/' + $("#State").val(),
            type: "post",
            datatype: "json",
            success: function (data) {
                if (data.length == 0) {
                    $("<option></option>")
                    .val("0")
                    .text("请选择市区")
                    .appendTo($("#City"));
                }
                $.each(data, function (i, item) {
                    $("<option></option>")
                    .val(item["Id"])
                    .text(item["Name"])
                    .appendTo($("#City"));
                });
                GetHospitalByID();
            }
        });
    }
    function GetHospitalByID() {
        $("#Hospital").empty();
        $.ajax({
            url: '/Doctor/ChangeHospital/' + $("#City").val(),
            type: "post",
            datatype: "json",
            success: function (data) {
                if (data.length == 0) {
                    $("<option></option>")
                    .val("0")
                    .text("请选择医院")
                    .appendTo($("#Hospital"));
                }
                $.each(data, function (i, item) {
                    $("<option></option>")
                    .val(item["Id"])
                    .text(item["Name"])
                    .appendTo($("#Hospital"));
                });
            }
        });
    }

 后台写法

        private void BindState()
        {
            AreaInfoRepository areaBll = new AreaInfoRepository();
            var stateList = areaBll.QueryParent(0);
            if (stateList == null)
            {
                stateList = new List<AreaInfoModel>();
            }

            var select = new List<SelectListItem>();
            foreach (var item in stateList)
            {
                select.Add(new SelectListItem { Text = item.Name, Value = item.Id.ToString() });
            }
            select.Insert(0, new SelectListItem { Text = "请选择省", Value = "0" });

            ViewBag.StateList = select;

            var city = new List<SelectListItem>();
            city.Insert(0, new SelectListItem { Text = "请选择市区", Value = "0" });
            ViewBag.CityList = city;
        }

        private void BindHospital()
        {
            HospitalRepository roleBll = new HospitalRepository();
            var list = roleBll.Query();
            if (list == null)
            {
                list = new List<HospitalModel>();
            }

            var select = new List<SelectListItem>();
            foreach (var item in list)
            {
                select.Add(new SelectListItem { Text = item.Name, Value = item.Id.ToString() });
            }
            select.Insert(0, new SelectListItem { Value = "0", Text = "请选择医院" });
            ViewBag.HospitalList = select;
        }

        public ActionResult ChangeCity(int id = 0)
        {
            AreaInfoRepository areaBll = new AreaInfoRepository();
            var cityList = new List<AreaInfoModel>();
            if (id != 0)
            {
                cityList = areaBll.QueryParent(id);
                if (cityList == null)
                {
                    cityList = new List<AreaInfoModel>();
                }
            }
            return Json(cityList, JsonRequestBehavior.AllowGet);
        }

        public ActionResult ChangeHospital(int id = 0)
        {
            HospitalRepository hospBLL = new HospitalRepository();
            var hospList = new List<HospitalModel>();
            if (id != 0)
            {
                hospList = hospBLL.QueryParent(id);
                if (hospList == null)
                {
                    hospList = new List<HospitalModel>();
                }
            }
            return Json(hospList, JsonRequestBehavior.AllowGet);
        }

        [HttpPost]
        public ActionResult Form(ExpertRegisterModel model)
        {
            BindNation();
            BindJobTitle();
            BindState();
            model.Doctor.Id = 0;
            if (ModelState.IsValid)
            {
                var form = HttpContext.Request.Form;
                if (form.Count > 0)
                {
                    var name = form["State"].ToString();
                    var hospital = form["Hospital"].ToString();
                    if (name != "")
                    {
                        model.Doctor.DominID = int.Parse(name);
                        model.Doctor.Hospital = int.Parse(hospital);
                    }
                    model.Doctor.ChargeUnit = form["ChargeUnitList"].ToString();
                }
                if (model.Doctor.Id == 0)
                {
                    bll.AddExpand(model);
                }
                else
                {
                    bll.UpdateExpand(model.Doctor.Id, model);
                }
                ViewBag.Msg = "编辑成功！";
                ViewBag.ReturnUrl = "Form";
            }
            var goOn = HttpContext.Request.Form["isGoOnAdd"];
            if (goOn == null || goOn.ToString() == "false")
            {
                return RedirectToAction("List");
            }
            else
            {
                return View(new ExpertRegisterModel());
            }
        }