验证用户名是否存在

<script language="javascript" type="text/javascript"> function send_request(flag) { //创建XMLHttpRequest; http_request = false; if(window.XMLHttpRequest) { //　非IE　浏览器 http_request = new XMLHttpRequest(); } else if(window.ActiveXObject) { //IE try { http_request = new ActiveXObject("Msxml2.XMLHTTP");//较新版本的IE }catch(e) { try { http_request = new ActiveXOBject("Microsoft.XMLHTTP");//旧版本IE }catch(e){} } } else { window.alert("不能创建　XMLHttpRequest对象，无法应用Ajax"); return false; } //指定回调函数 if(flag == "addAdmin") { http_request.onreadystatechange = addAdmin; //创建HTTP请求 http_request.open("get","Handler.ashx?flag=addAdmin&userName="+document.getElementById("txtUserName").value,true); } else if(flag == "updateTitle") { http_request.onreadystatechange = updateTitle; //创建HTTP请求 i = document.getElementById("ddlVoteTitle").selectedIndex;//选择的索引 id = document.form1.ddlVoteTitle.options[i].value; http_request.open("get","Handler.ashx?flag=updateTitle&id="+id,true); } //发送上面创建的HTTP请求 http_request.send(null); } function addAdmin() { if(http_request.readyState == 4)//发送成功 { if(http_request.status == 200)//交易成功 { //正式处理有信息 if(http_request.responseText == "该用户已经存在") { //隐藏提交按扭 document.getElementById("Button1").style.display ="none"; } else { document.getElementById("Button1").style.display=""; } document.getElementById("lblShow").innerText=http_request.responseText; } } } function updateTitle() { if(http_request.readyState == 4)//发送成功 { if(http_request.status == 200)//交易成功 { //正式处理有信息 document.getElementById("lblTitle").innerText=http_request.responseText; } } } </script> ============================================================ public class Handler : IHttpHandler { DB DBManager = new DB(); public void ProcessRequest (HttpContext context) { context.Response.ContentType = "text/plain"; string flag = context.Request.QueryString["flag"].ToString(); if (flag.Equals("addAdmin")) { string userName = context.Request.QueryString["userName"].ToString(); string strSql = "select count(*) from admin where userName = '" + userName + "'"; if (Convert.ToInt32(DBManager.executeGetReturn(strSql)) > 0) { context.Response.Write("该用户已经存在"); } else { context.Response.Write("你可以注册［" + userName + "］"); } } else if (flag.Equals("updateTitle")) { int id = Convert.ToInt32(context.Request.QueryString["id"].ToString()); string strSql = "update voteConfig set id=" + id; if (DBManager.executeNonQuery(strSql) > 0) { context.Response.Write("设置已成功，当前系统前调查［" + DBManager.executeGetReturn("select voteTitle from voteMaster where id=" + id) + "］"); } else { context.Response.Write("设置失败"); } } } public bool IsReusable { get { return false; } } }