首先添加一个html页其页面代码如下:

<html>
<head>
<title>在ASP.NET的第一个Ajax小程序</title>
<link rel=”stylesheet” type=”text/css” href=”../css/main.css”/>
<script language=”javascript”>
        var xmlHttp
        function showHint(str)
        {
            if (str.length > 0)
            {
                var url=“GetRequest.aspx?name=“ + str
                if (window.ActiveXObject) { 
                    xmlHttp = new ActiveXObject(“Microsoft.XMLHTTP“); 
                }
                  xmlHttp.onreadystatechange=stateChanged
                xmlHttp.open(“POST“, url , true)
                xmlHttp.send(null)
            }
            else
            {
                document.getElementById(“txtHint“).innerHTML=“”
            }
        }
        function stateChanged()
        {
            if (xmlHttp.readyState==4 || xmlHttp.readyState==“complete“)
            {
                document.getElementById(“txtHint“).innerHTML=xmlHttp.responseText
            }
        }

</script>
</head><body>
<div class=content>
<h1>纯Ajax实现的小程序</h1>
<form>
    <p>输入一个字符串:<input type=”text” id=”txt1″onkeyup=”showHint(this.value)”></p>

<p>
    字符串的长度: <span id=”txtHint”></span></p> 
   </form> </div></body>
</html>

述代码中GetRequest.aspx?name=” + str 指明将请求页面GetRequest.aspx并把用户输入的字符串传递给页面GetRequest.aspx,所以下一步就是建立GetRequest.aspx页面计算字符串长度,后台代码如下:

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class PureAjax_GetRequest : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Request.QueryString[“name“] != “”)
            Response.Write(Request.QueryString[“name“].Length);
        else
            Response.Write(“NULL“);
    }
}

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