Ajax简单应用,检测用户名是否存在

客户端页面index.html

!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
html xmlns="http://www.w3.org/1999/xhtml"
head
titleajax测试用户名是否存在/title
script language="javascript" type="text/javascript"
//生成Http请求对象，用于客户端向服务/端发送异步的http请求
function getHttpObject()
{
var http;
var browser = navigator.appName;

if(browser == "Microsoft Internet Explorer")
{
//如果用户使用IE，就返回XMLHTTP的ActiveX对象
http = new ActiveXObject("MSXML2.XMLHTTP.3.0");
}
else
{
//否则返回一个XMLHttpRequest对象
http = new XMLHttpRequest();
}

return http;
}
//获取全局的HTTP请求对象
var http = getHttpObject();

//处理请求状态变化
function getHello()
{
//4表示请求已完成
if (http.readyState == 4)
{

//获取服务段的响应文本

var helloStr = http.responseText;
alert(helloStr);
if(helloStr.charAt(0)!="0")
{alert("用户名已经存在!");}
else
{alert("用户名不存在,可以实用!");}
}
}
function HelloWorld()
{
var url = "Check.aspx？id="+document.getElementById("Text1").value;

//指定服务端的地址
http.open("GET", url, true);
//请求状态变化时的处理函数
http.onreadystatechange = getHello;
//发送请求
http.send(null);
}

/script

/head
body
input id="Text1" style="width: 116px" type="text" /
input id="Button1" type="button" value="button" onclick="javascript：HelloWorld();" /

/body
/html

服务器端功能页面Check.aspx

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;
using System.Data.SqlClient;

public partial class Check : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
string str = "select Count(*) from Table where Name=" + Request.QueryString["id"].ToString() + "";
SqlConnection conn = new SqlConnection("Data Source=.;Initial Catalog=Database;Integrated Security=True");
conn.Open();
SqlCommand cmd = new SqlCommand(str, conn);
int i = (int)cmd.ExecuteScalar();
conn.Close();
Response.Write(i);
}
}