<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="ICallBackEventHandlerSample._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>ICallbackEventHandlertitle>
    <script language="javascript" type="text/javascript">
        function GetResult(returnValue,
context) {
            document.getElementById("txtDateTime").value = returnValue;
        }
        function Request()
{
            CallServer();
            return
false;
        }
    script>
head>
<body>
    <form id="form1" runat="server">
    <asp:TextBox ID="txtDateTime" runat="server" Text="">
    asp:TextBox>
    <asp:Button ID="btnDateTime" OnClientClick="return Request()" runat="server"
        Text="Get Server Date
Time" />
    form>
body>
html>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text;
namespace ICallBackEventHandlerSample
{
public partial class _Default : System.Web.UI.Page, ICallbackEventHandler
    {
protected void Page_Load(object sender, EventArgs e)
        {
            ClientScriptManager scriptManager = Page.ClientScript; 
            String cbReference = scriptManager.GetCallbackEventReference
(this, "returnValue", "GetResult", "context");
String callbackScript = "function CallServer(returnValue, context)
{" + cbReference + "; }";
            scriptManager.RegisterClientScriptBlock(this.GetType(),
"CallServer", callbackScript, true);
}
        private string returnValue;
        public string GetCallbackResult()
        {
            return returnValue;
}
public void RaiseCallbackEvent(string eventArgument)
        {
            returnValue = DateTime.Now.ToString();
        }      
    }
} 
 
