谈到ajax异步刷新技术，我之前感觉很高深，今天看了一下，大体上有一个了解，AJAX最大的应用就是我们要理解XMLHttpRequest这个对象。XMLHttpRequest可以提供不重新加载页面的情况下更新网页，在页面加载后在客户端向服务器请数 据， 在  页面加载后在服务器端接受数据，在后台向客户端发送数据。

关于ajax的详细叙述，可以参考这个博客：http://www.blogjava.net/tbwshc/archive/2012/07/24/383857.html

然后我贴出一些原始的ajax的例子，这样更方便了解ajax原理，解开他神奇的面纱，当然现在使用jQuery的ajax封装方法也非常方便。

例1：get请求

get.ashx:

<%@ WebHandler Language="C#" Class="_01_get" %>  using System; using System.Web;  public class _01_get : IHttpHandler {          public void Proce***equest (HttpContext context) {         context.Response.ContentType = "text/plain";         //int m = 0;         //int n = 5 / m;                  //System.Threading.Thread.Sleep(3000);         context.Response.Write(DateTime.Now.ToString());     }       public bool IsReusable {         get {             return false;         }     }  }

get.htm:

例2：post请求提交保单

post.ashx:

<%@ WebHandler Language="C#" Class="_02_post" %>  using System; using System.Web;  public class _02_post : IHttpHandler {          public void Proce***equest (HttpContext context) {         context.Response.ContentType = "text/plain";          string name = context.Request.Form["n"];         string pwd = context.Request.Form["p"];         if (name == "admin" && pwd == "admin")         {             context.Response.Write(1);         }         else         {             context.Response.Write(0);         }     }       public bool IsReusable {         get {             return false;         }     }  }


post.htm:

例3：省市选择效果

pro.ashx:

<%@ WebHandler Language="C#" Class="_06_pro" %>  using System; using System.Web; using System.Collections.Generic; using System.Text; public class _06_pro : IHttpHandler {          public void Proce***equest (HttpContext context) {         context.Response.ContentType = "text/plain";         string s = context.Request.QueryString["pid"];         int pid;         if (int.TryParse(s, out pid))         {              //json形式的字符串             string json = GetDataByPId(pid);             context.Response.Write(json);         }         else             {             context.Response.Write("[]");         }     }     private string GetDataByPId(int pid)     {         List list = GetAllDatas();          List wantedList = new List();         foreach (Data data in list)         {             if (data.Pid == pid)             {                 wantedList.Add(data);             }         }                  //拼json形式的字符串             //[{ "Id": 1, "Name": "河北省", "PId": 0 },          //            { "Id": 2, "Name": "日本省", "PId": 0 },          //            { "Id": 3, "Name": "台湾省", "PId": 0 }          // ]         StringBuilder sb = new StringBuilder();         sb.Append("[");          foreach (Data data in wantedList)         {             sb.Append("{ \"Id\": "+data.Id+", \"Name\": \""+data.Name+"\", \"PId\": "+data.Pid+" },");         }         sb.Remove(sb.Length - 1, 1);         sb.Append("]");         return sb.ToString();     }          ///      /// 模拟从数据库中加载数据，返回泛型集合     ///      ///      private List GetAllDatas()     {         List list = new List();          list.Add(new Data() { Id = 1, Name = "河北省", Pid = 0 });         list.Add(new Data() { Id = 2, Name = "台湾省", Pid = 0 });         list.Add(new Data() { Id = 3, Name = "日本省", Pid = 0 });           list.Add(new Data() { Id = 4, Name = "石家庄", Pid = 1 });         list.Add(new Data() { Id = 5, Name = "邯郸市", Pid = 1 });         list.Add(new Data() { Id = 6, Name = "邢台市", Pid = 1 });          list.Add(new Data() { Id = 7, Name = "高雄市", Pid = 2 });         list.Add(new Data() { Id = 8, Name = "台北", Pid = 2 });         list.Add(new Data() { Id = 9, Name = "台中", Pid = 2 });          list.Add(new Data() { Id = 10, Name = "东京", Pid = 3 });         list.Add(new Data() { Id = 11, Name = "冲绳", Pid = 3 });         list.Add(new Data() { Id = 12, Name = "大阪", Pid = 3 });         return list;     }     public bool IsReusable {         get {             return false;         }     }  }

pro.htm:

自己封装的ajax：

function my$(id) {     return document.getElementById(id); }  var xhr = createXHR(); function createXHR() {     var request;     if (XMLHttpRequest) {         request = new XMLHttpRequest();      } else {         request = new ActiveXObject("Microsoft.XMLHTTP");     }     return request; }  function ajax(method,url,data,fnSuccess,fnError) {      xhr.open(method, url, true);     if (method == "post") {         //!------------------!注意         xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");     }     xhr.onreadystatechange = function () {         if (xhr.readyState == 4) {                        if (xhr.status == 200) {                 var s = xhr.responseText;                 fnSuccess(s);             } else {                 fnError();             }         }     }     xhr.send(data); }

这里要感谢刘兄的指导，在此鸣谢！

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