动态显示文本框的字符串数(ajax入门小程序)

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");
    }
}