JQuery+Ajax制作省市联动

$(document).ready(function () {
            $("#Province").append("<option value=''>" + "--请选择--" + "</option>");
            $("#City").append("<option value=''>" + "--请选择--" + "</option>");
            $("#District").append("<option value=''>" + "--请选择--" + "</option>");
            $.ajax({
                url: "Handler1.ashx?type=0", //路径 地址
                type: "get", //类型，post\get
                dataType: "json", //json数据
                success: function (msg) {//返回结果   
                    for (var i = 0; i < msg.length; i++) {
                        $("#Province").append("<option value='" + msg[i].ProvinceID + "'>" + msg[i].ProvinceName + "</option>");
                    }
                }
            });
            //市
            $("#Province").change(function () {
                $("#City").empty(); //清空数据
                $("#District").empty(); //清空数据
                $("#District").append("<option value=''>" + "--请选择--" + "</option>");
                var ProvinceID = $(this).val();
                
                $.ajax({
                    url: "Handler1.ashx?type=1",
                    type: "get", //类型
                    data: {
                        ProvinceID: ProvinceID
                    },
                    dataType: "json", //json数据
                    success: function (msg) {
                        for (var i = 0; i < msg.length; i++) { $("#City").append("<option value='" + msg[i].CityID + "'>" + msg[i].CityName + "</option>"); }
                    }
                });
            });

            //区
            $("#City").change(function () {
                $("#District").empty(); //清空数据
                var CityID = $(this).val();
                $.ajax({
                    url: "Handler1.ashx?type=2",
                    type: "get", //类型
                    data: {
                        CityID: CityID
                    },
                    dataType: "json", //json数据  
                    success: function (msg) {
                        for (var i = 0; i < msg.length; i++) { $("#District").append("<option value='" + msg[i].DistrictID + "'>" + msg[i].DistrictName + "</option>"); }
                    }
                });

            });
        });

<select id="Province"></select>
<select id="City"></select>
<select id="District" ></select>
        

结合ajax（一般处理程序）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data;
using System.Web.Script.Serialization;

namespace GovSystem.Company
{
    /// <summary>
    /// Handler1 的摘要说明
    /// </summary>
    public class Handler1 : IHttpHandler
    {
       
        public string text;
        public void ProcessRequest(HttpContext context)
        {
            int action = Convert.ToInt32(context.Request.QueryString["type"]);
            switch (action)
            {
                case (int)GetType.省:
                    text = Sel_Province(context);
                    break;
                case (int) GetType.市:
                    text=Sel_City(context);
                    break;
                case (int)GetType.区:
                    text = Sel_District(context);
                    break;
            }
            context.Response.ContentType = "text/plain";
            context.Response.Write(text);
        }
        //省
        private string Sel_Province(HttpContext context)
        {
            XieKe.BLL.S_Province b_Province = new XieKe.BLL.S_Province();
            DataTable dt=b_Province.GetList("").Tables[0];
            List<XieKe.Model.S_Province> listInfo = new List<XieKe.Model.S_Province>();
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                XieKe.Model.S_Province m_Province = new XieKe.Model.S_Province { ProvinceID = long.Parse(dt.Rows[i]["ProvinceID"].ToString()), DateCreated = Convert.ToDateTime(dt.Rows[i]["DateCreated"]), DateUpdated = Convert.ToDateTime(dt.Rows[i]["DateUpdated"]), ProvinceName = dt.Rows[i]["ProvinceName"].ToString() };
                listInfo.Add(m_Province);
            }
            JavaScriptSerializer jssp = new JavaScriptSerializer();
            string s= jssp.Serialize(listInfo);
            return s;
        }
        //市
        private string Sel_City(HttpContext context)
        {
            string ProvinceID = context.Request.QueryString["ProvinceID"];
            XieKe.BLL.S_City b_City = new XieKe.BLL.S_City();

            DataTable dt = b_City.GetList("ProvinceID="+ProvinceID).Tables[0];
            List<XieKe.Model.S_City> listInfo = new List<XieKe.Model.S_City>();
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                XieKe.Model.S_City m_City = new XieKe.Model.S_City { CityID = long.Parse(dt.Rows[i]["CityID"].ToString()), CityName = dt.Rows[i]["CityName"].ToString(), DateCreated = Convert.ToDateTime(dt.Rows[i]["DateCreated"]), DateUpdated = Convert.ToDateTime(dt.Rows[i]["DateUpdated"]), ProvinceID = long.Parse(dt.Rows[i]["ProvinceID"].ToString()), ZipCode = dt.Rows[i]["ZipCode"].ToString() };
                listInfo.Add(m_City);
            }
            JavaScriptSerializer jssp = new JavaScriptSerializer();
            return jssp.Serialize(listInfo);
        }
        //区
        private string Sel_District(HttpContext context)
        {
            string CityID = context.Request.QueryString["CityID"];
            XieKe.BLL.S_District b_City = new XieKe.BLL.S_District();
            DataTable dt = b_City.GetList("CityID=" + CityID).Tables[0];
            List<XieKe.Model.S_District> listInfo = new List<XieKe.Model.S_District>();
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                XieKe.Model.S_District m_District = new XieKe.Model.S_District { CityID = Convert.ToInt32(dt.Rows[i]["CityID"]), DistrictName = dt.Rows[i]["DistrictName"].ToString() };
                listInfo.Add(m_District);
            }
            JavaScriptSerializer jssp = new JavaScriptSerializer();
            return jssp.Serialize(listInfo);
        }
        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
        public enum GetType
        {
            省 = 0,
            市 = 1,
            区 = 2,
        };
    }
  
}