1、jquery代码

function getCity(CityVal) {
    var DDL_Province = $("#DDL_Province");
    var DDL_City = $("#DDL_City");
    DDL_City.empty();
    DDL_City.append("<option value=\"0\">市/区</option>");
    $.ajax(
    {
        type: "post",
        url: "/UserCart/Controller/CityAreas.ashx",
        data: { "type": "city", "provinceID": DDL_Province.val() },
        dataType: "json",
        async: false,
        success: function (msg) {

            for (var i = 0; i < msg.length; i++) {

                if (CityVal == msg[i].CityName) {
                    if (msg[i].IsCOD == 1) {
                        DDL_City.append("<option value=" + msg[i].CityID + " selected=\"selected\">" + msg[i].CityName + "*</option>");
                    } else {
                        DDL_City.append("<option value=" + msg[i].CityID + " selected=\"selected\">" + msg[i].CityName + "</option>");
                    }
                } else {
                    if (msg[i].IsCOD == 1) {
                        DDL_City.append("<option value=" + msg[i].CityID + " >" + msg[i].CityName + "*</option>");
                    } else {
                        DDL_City.append("<option value=" + msg[i].CityID + " >" + msg[i].CityName + "</option>");
                    }
                }
            }
            getArea('');
            GetAddreesSpan();
        }
    })
};

function getArea(AreaVal) {

    var DDL_City = $("#DDL_City");
    var DDL_Area = $("#DDL_Area");
    DDL_Area.empty();
    DDL_Area.append("<option value=\"0\">县/乡</option>");
    $.ajax(
    {
        type: "post",
        url: "/UserCart/Controller/CityAreas.ashx",
        data: { "type": "district", "cityID": DDL_City.val() },
        dataType: "json",
        async: false,
        success: function (msg) {

            for (var i = 0; i < msg.length; i++) {
                if (AreaVal == msg[i].DistrictName) {
                    if (msg[i].IsCOD == 1) {
                        DDL_Area.append("<option value=" + msg[i].DistrictID + "  selected=\"selected\">" + msg[i].DistrictName + "*</option>");
                    } else {
                        DDL_Area.append("<option value=" + msg[i].DistrictID + "  selected=\"selected\">" + msg[i].DistrictName + "</option>");
                    }
                } else {

                    if (msg[i].IsCOD == 1) {
                        DDL_Area.append("<option value=" + msg[i].DistrictID + " >" + msg[i].DistrictName + "*</option>");
                    } else {
                        DDL_Area.append("<option value=" + msg[i].DistrictID + " >" + msg[i].DistrictName + "</option>");
                    }
                }


            }
            GetAddreesSpan();
        }
    })

};

function GetAddreesSpan() {


}

2、后端C#代码

<%@ WebHandler Language="C#" Class="CityAreas" %>

using System;
using System.Web;
using System.Collections.Generic;

public class CityAreas : IHttpHandler
{

    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "text/plain";
        if (context.Request["type"] == "city")
        {
            context.Response.Write(select2(context.Request["provinceID"]));
        }
        else if (context.Request["type"] == "district")
        {
            context.Response.Write(select3(context.Request["cityID"]));
        }
    }


    public string select2(string id)
    {
        string str = string.Empty;
        if (!string.IsNullOrEmpty(id))
        {
            List<ECS.Model.A_CityAreas> list = new ECS.BLL.A_CityAreas().GetList(null, "deep=2 and ParentID=" + id, null);
            if (list != null && list.Count > 0)
            {
       
                System.Text.StringBuilder sb = new System.Text.StringBuilder();
                sb.Append("[");
                foreach (ECS.Model.A_CityAreas item in list)
                {
                    sb.Append("{");
                    sb.Append("\"CityID\":\"" + item.id + "\",\"CityName\":\"" + item.AreaName + "\",\"IsCOD\":\"" + item.IsCOD + "\"");
                    sb.Append("},");
                }
                sb.Remove(sb.Length - 1, 1);
                sb.Append("]");
                str = sb.ToString();
            }
           
        }
        return str;
    }

    public string select3(string id)
    {
        string str = string.Empty;
        if (!string.IsNullOrEmpty(id))
        {
            List<ECS.Model.A_CityAreas> list = new ECS.BLL.A_CityAreas().GetList(null, "deep=3 and ParentID=" + id, null);
            if (list != null && list.Count > 0)
            {
              
                System.Text.StringBuilder sb = new System.Text.StringBuilder();
                sb.Append("[");
                foreach (ECS.Model.A_CityAreas item in list)
                {
                    sb.Append("{");
                    sb.Append("\"DistrictID\":\"" + item.id + "\",\"DistrictName\":\"" + item.AreaName + "\",\"IsCOD\":\"" + item.IsCOD + "\"");
                    sb.Append("},");
                }
                sb.Remove(sb.Length - 1, 1);
                sb.Append("]");
                str = sb.ToString();
            }
           
        }
        return str;
    }
    public bool IsReusable
    {
        get
        {
            return false;
        }
    }

}