How to achieve non-refresh linkage of drop-down box with Ajax

@{ Layout = null; } @using DAL; @using System.Data; @{ AreaDal areaDal = new AreaDal(); string areaId = ViewBag.areaId; DataRow drArea = areaDal.GetArea(areaId); string countyId = drArea == null ? "-1" : drArea["countyId"].ToString(); DataRow drCounty = areaDal.GetCounty(countyId); string cityId = drCounty == null ? "-1" : drCounty["cityId"].ToString(); DataRow drCity = areaDal.GetCity(cityId); string provinceId = drCity == null ? "-1" : drCity["provinceId"].ToString(); }      
   ==请选择==   ==请选择==   ==请选择==   ==请选择==    

using System; using System.Collections.Generic; using System.Data; using System.Linq; using System.Text; using System.Web.Mvc; using DAL; namespace Controllers.Backstage { /// 
 /// 行政区划 /// 
 public class AreaController : AdminBaseController { #region 构造函数及变量 private SQLiteHelper.SQLiteHelper sqliteHelper; private AreaDal areaDal; public AreaController() { sqliteHelper = new SQLiteHelper.SQLiteHelper(); areaDal = new AreaDal(); } #endregion #region 行政区划商圈级联选择页面 public ActionResult AreaSelect() { return PartialView(); } #endregion #region 获取全部省 public ActionResult GetProvinces() { DataTable dt = areaDal.GetProvincesAll(); StringBuilder sbHtml = new StringBuilder(); sbHtml.Append("==请选择=="); foreach (DataRow dr in dt.Rows) { sbHtml.AppendFormat("{1}", dr["id"].ToString(), dr["name"].ToString()); } return Content(sbHtml.ToString()); } #endregion #region 根据省获取市 public ActionResult GetCities(string provinceId) { DataTable dt = areaDal.GetCities(provinceId); StringBuilder sbHtml = new StringBuilder(); sbHtml.Append("==请选择=="); foreach (DataRow dr in dt.Rows) { sbHtml.AppendFormat("{1}", dr["id"].ToString(), dr["name"].ToString()); } return Content(sbHtml.ToString()); } #endregion #region 根据市获取区县 public ActionResult GetCounties(string cityId) { DataTable dt = areaDal.GetCounties(cityId); StringBuilder sbHtml = new StringBuilder(); sbHtml.Append("==请选择=="); foreach (DataRow dr in dt.Rows) { sbHtml.AppendFormat("{1}", dr["id"].ToString(), dr["name"].ToString()); } return Content(sbHtml.ToString()); } #endregion #region 根据区县获取商圈 public ActionResult GetAreas(string countyId) { DataTable dt = areaDal.GetAreas(countyId); StringBuilder sbHtml = new StringBuilder(); sbHtml.Append("==请选择=="); foreach (DataRow dr in dt.Rows) { sbHtml.AppendFormat("{1}", dr["id"].ToString(), dr["name"].ToString()); } return Content(sbHtml.ToString()); } #endregion } }