<script type="text/javascript">

        $(function () {

            loadProvince();

            loadCity();

        });

        function loadProvince() {

            $.ajax({

                type: "get",

                url: "province_city.ashx",

                data: "pid=-1",

                async: false,//同步

                success: function (json) {

                    var jsons = eval(json);

                    var province = document.getElementById("province");

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

                        var p = jsons[i];

                        if (p.Pid == -1) {

                            var option = document.createElement("option");

                            option.value = p.Id;

                            option.innerHTML = p.Name;

                            province.appendChild(option);

                        }

                    }

                }

            });

        };

        //加载市

        function loadCity() {

            city.innerHTML = "";//清空控件内容

            var pid = document.getElementById("province").value;//获得省的pid

            $.ajax({

                type: "get",

                url: "province_city.ashx",

                data: "pid=" + pid,

                success: function (json) {

                    var jsons = eval(json);

                    var city = document.getElementById("city");

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

                        var c = jsons[i];

                        var option = document.createElement("option");

                        option.value = c.Id;

                        option.innerHTML = c.Name;

                        city.appendChild(option);

                    }

                }

            });

        };

    </script>

        public void ProcessRequest(HttpContext context)

        {

            context.Response.ContentType = "text/plain";

            string s= context.Request.QueryString["pid"];

            int pid;

            if (int.TryParse(s,out pid))

            {

                string json = GetDataByPid(pid);

                context.Response.Write(json);

            }

        }

        private string GetDataByPid(int pid)

        {

            List<Data> list = GetAllDatas();

            List<Data> datas = new List<Data>();

            foreach (Data item in list)

            {

                if (item.Pid == pid)

                {

                    datas.Add(item);

                }

            }

            //把对象转换成json格式的字符串

            JavaScriptSerializer jss = new JavaScriptSerializer();

            string json = jss.Serialize(datas);

            return json;

        }

        private List<Data> GetAllDatas()

        {

            List<Data> list = new List<Data>();

            list.Add(new Data() { Id = , Name = "河南省", Pid = - });

            list.Add(new Data() { Id = , Name = "台湾省", Pid = - });

            list.Add(new Data() { Id = , Name = "日本省", Pid = - });

            list.Add(new Data() { Id = , Name = "郑州市", Pid =  });

            list.Add(new Data() { Id = , Name = "济源市", Pid =  });

            list.Add(new Data() { Id = , Name = "焦作市", Pid =  });

            list.Add(new Data() { Id = , Name = "高雄市", Pid =  });

            list.Add(new Data() { Id = , Name = "台北", Pid =  });

            list.Add(new Data() { Id = , Name = "台中", Pid =  });

            list.Add(new Data() { Id = , Name = "东京", Pid =  });

            list.Add(new Data() { Id = , Name = "冲绳", Pid =  });

            list.Add(new Data() { Id = , Name = "大阪", Pid =  });

            return list;

        }