Ajax Control ToolKit question


<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %><%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
<!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>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:ScriptManager ID="ScriptManager1" runat="server" 
            AsyncPostBackErrorMessage="出错了" AsyncPostBackTimeout="2">
        </asp:ScriptManager>
        <asp:TextBox ID="txtTest" runat="server"></asp:TextBox>
        <asp:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server"
         ServicePath="~/WebService.asmx"
         ServiceMethod="getstring"
         TargetControlID="txtTest"
         CompletionInterval="500"
         CompletionSetCount="10"
         MinimumPrefixLength="1"
        >
        </asp:AutoCompleteExtender>
        
    </div>
    </form>
</body>
</html>web servicesusing System.Web.Services;
using System.Data;
using System.Web.Script.Services;/// <summary>
///WebService 的摘要说明
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
//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 WebService : System.Web.Services.WebService
{
    public WebService () {        //如果使用设计的组件，请取消注释以下行 
        //InitializeComponent(); 
    }
   [WebMethod]
   public string[] getstring(string prefixText, int count)
    {
        Operation op=new Operation();
        DataTable da=op.Seach("Dic_wuzi_guanli_bianma",null,new string[]{"top("+count+") [name]"},new string[]{"[name] like '"+prefixText+"%'"});
        if (da.Rows.Count > 0)
        {
            string[] aa = new string[da.Rows.Count];
            for (int i = 0; i < da.Rows.Count; i++)
            {
                aa[i] = da.Rows[i]["name"].ToString();
            }
            return aa;
        }
       else
    {
       return new string[]{""}
    }
    }
    
}