Jquery+WebService 校验账号是否已被注册

在Javascirpt代码中，调用Jquery的方法$.Ajax(function)实现Ajax,传递账号信息给Web服务，
Web服务再调用数据库操作类查询数据库，并返回数据给前台页面。详细代码如下：

Default.aspx

<% @ Page Language = " C# "  AutoEventWireup = " true "  CodeBehind = " Default.aspx.cs "  Inherits = " Ajax_XML._Default "   %>

<! 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 runat = " server " >
     < title >< / title>
< script type = " text/javascript "  src = " jquery-1.3.2-vsdoc2.js "  language = " javascript " >< / script>
< script type = " text/javascript "  language = " javascript " >
    $( function () {
        $( " #<%=UserID.ClientID%> " ).keyup(
                 function () {
                    $.ajax({
                        type:  " POST " ,
                        contentType:  " application/json " ,
                        dataType:  " json " ,
                        url:  " WebService1.asmx/UserIsExist " ,
                        data:  " {UserID:' "   +  $( " #<%=UserID.ClientID%> " ).val()  +   " '} " ,
                        success:  function (result) {
                             if  (result.d  ==   " true " )
                                $( " #<%=IsExist.ClientID%> " ).text( " Yes " );　　//账号已存在
                             else
                                $( " #<%=IsExist.ClientID%> " ).text( " No " );　　
                        }
                      
                    });
                }
                );

    })

< / script>
< / head>

< body >
     < form id = " form1 "  runat = " server " >
     < div >
    
         < table style = " width:100%; " >
             < tr >
                 < td >
                     & nbsp; < / td>
                 < td >
                     & nbsp; < / td>
                 < td >
                     & nbsp; < / td>
             < / tr>
             < tr >
                 < td >
                     & nbsp; < / td>
                 < td >
                     < asp:TextBox ID = " UserID "  runat = " server " >< / asp:TextBox>
                     < asp:Label ID = " IsExist "  runat = " server "  Visible = " true " >< / asp:Label>
                 < / td>
                 < td >
                     & nbsp; < / td>
             < / tr>
             < tr >
                 < td >
                     & nbsp; < / td>
                 < td >
                     & nbsp; < / td>
                 < td >
                     & nbsp; < / td>
             < / tr>
         < / table>
    
     < / div>
     < / form>
< / body>
< / html>

 

WebService1.asmx.cs

using  System;
using  System.Collections.Generic;
using  System.Linq;
using  System.Web;
using  System.Web.Services;
using  System.Data;
using  System.Data.SqlClient;
using  System.Configuration;
using  System.Text;
using  DAL;

namespace  Ajax_XML
{
     ///   <summary>
     ///  WebService1 的摘要说明
     ///   </summary>
    [WebService(Namespace  =   " http://tempuri.org/ " )]
    [WebServiceBinding(ConformsTo  =  WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem( false )]
     //  若要允许使用 ASP.NET AJAX 从脚本中调用此 Web 服务，请取消对下行的注释。
     [System.Web.Script.Services.ScriptService]
     public   class  WebService1 : System.Web.Services.WebService
    {

        [WebMethod]
         public   string  HelloWorld()
        {

             return   " Hello,World! " ;
        }
        [WebMethod]
         public   string  UserIsExist( string  UserID)
        {
            
             string  sql  =   string .Format( " select * from Customers where FirstName=' "   +  UserID + " ' " );

             using  (SqlDataReader dr  =  SqlHelper.ExecuteSql(sql))
            {
                 if  (dr.Read())
                     return   " false " ;
                 else
                     return   " true " ;
            }

            

        }
    }
}