【转】 ASP.NET使用ICallbackEventHandler无刷新验证用户名是否可用

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
using System.Data.Common;

public partial class Ver : System.Web.UI.Page,ICallbackEventHandler
{
    public string sCallBackFunctionInvocation;
    //接收前台传入的值
    string userName = "";

    void Page_Load(object sender, System.EventArgs e)
    {
        //注册脚本到前台
        sCallBackFunctionInvocation = Page.ClientScript.GetCallbackEventReference(this, "message", "ShowMessage", "context");
    }

    #region ICallbackEventHandler 成员

    public string GetCallbackResult()
    {
        using (SqlConnection conn = new SqlConnection(
            System.Configuration.ConfigurationManager.AppSettings["ConnStr"]))
        {
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = string.Format(
                "Select Count(*) From PUsers Where UserName=‘{0}‘",
                userName);
            conn.Open();
            if (int.Parse(cmd.ExecuteScalar().ToString()) == 1)
            {
               return "false";
            }
            else
            {
               return "true";
            }
        }
    }
    //接收前台参数
    public void RaiseCallbackEvent(string eventArgument)
    {
        userName = eventArgument;
    }

    #endregion
}