ASP.NET中AJAX的异步加载（Demo演示）

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此次的Demo是一个页面，页面上有两行字，然后后面用AJAX，使用一个下拉框去替换第一行文字[/code]

第一个是被替换的网页

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <title></title>
  <script type="text/javascript">
    var xmlHttpRequest;
    function createXmlHttpRequest() {
      if (window.ActiveXObject) {
        xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP");//IE浏览器
      } else {
        xmlHttpRequest = new window.XMLHttpRequest();//谷歌等浏览器
      }
    }

    function sendRequest() {
      createXmlHttpRequest();//获取对象
      xmlHttpRequest.onreadystatechange = function () {
        if (xmlHttpRequest.readyState == 4) {
          if (xmlHttpRequest.status == 200) {
            document.getElementById("divContent").innerHTML = xmlHttpRequest.responseText;
          }
        }
      };
      xmlHttpRequest.open("POST", "DeptHandler.ashx", true);
      xmlHttpRequest.send(null);
    }

  </script>
  <!--<script type="text/javascript">
    var xmlHttpRequest;
    function createXMLHttpRequest() {
      if (window.ActiveXObject) {
        xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP");//IE浏览器
      } else {
        xmlHttpRequest = new window.XMLHttpRequest();//谷歌等浏览器
      }
    }
    //请求数据
    function sendRequest() {
      createXMLHttpRequest();
      xmlHttpRequest.onreadystatechange = function () {
        if (xmlHttpRequest.readState == 4) {
          if (xmlHttpRequest.status == 200) {
            document.getElementById("divContent").innerHTML = xmlHttpRequest.responseText;
          }
        }
      }
      xmlHttpRequest.open("POST", "DeptHandler.ashx", true);

      xmlHttpRequest.send(null);
    }
  </script>-->
</head>
<body>
  <div>
    <div id="divContent">
       
      <p style="color:red">这里显示部门信息</p>
    </div>
    <script type="text/javascript">sendRequest()</script>
    <div>
      <p style="color:red">这里显示部门信息结束了</p>
    </div>
  </div>
</body>
</html>

第二个是一个类

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

namespace WebApplication2
{
  public class Dept
  {
    public int Id { get; set; }

    public string DeptName { get; set; }
  }
}

然后是一个一般处理程序

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Web;

namespace WebApplication2
{
  /// <summary>
  /// DeptHandler 的摘要说明
  /// </summary>
  public class DeptHandler : IHttpHandler
  {

    public void ProcessRequest(HttpContext context)
    {
      //这里的AJAX进行了三秒的延迟
      Thread.Sleep(3000);
      List<Dept> depts = new List<Dept>
      {
        new Dept(){Id=1,DeptName="财务部"},
        new Dept(){Id=2,DeptName="研发部"},
        new Dept(){Id=3,DeptName="市场部"}
      };
      StringBuilder sb = new StringBuilder();
      sb.AppendLine("<select>");
      foreach (var item in depts)
      {
        sb.AppendLine($"<option id = {item.Id}>{item.DeptName}</option>");
      }
        
      sb.AppendLine("</select>");
      context.Response.ContentType = "text/plain";
      context.Response.Write(sb);


    }

    public bool IsReusable
    {
      get
      {
        return false;
      }
    }
  }
}

效果图

AJAX有三秒的延迟加载

前三秒