CustomValidator with XMLHttpRequest object

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.ComponentModel;
using System.IO;
using System.Web;
using System.Drawing.Design;
using System.Collections.Specialized;  

namespace Gilat
{
	/// <summary>
	/// GilatValidator makes XMLHTTPRequest
	/// to server to validate without full page refresh
	/// </summary>
	[DefaultProperty("Text"), ToolboxData("<{0}:GilatValidator runat=server></{0}:GilatValidator>")]
	public class GilatValidator : System.Web.UI.WebControls.CustomValidator
	{
		//function makes XMLHTTPRequest
		const string XMLHTTPRequestScript = @"
		<script language='javascript'>

			//GilatControlsUtils.RegisterXMLHTTPRequestScript
			function doXMLHTTPRequest(Url)
			{
				var oXMLHTTP = new ActiveXObject(""Microsoft.XMLHTTP"");
	
				oXMLHTTP.open(""POST"", Url, false);

				try
				{
					oXMLHTTP.send();
					return oXMLHTTP.responseText;
				}	
				catch(e) 
				{
					alert(""XMLHTTPRequest failed"");
					return """";
				}

			}
		</script>";

		string GilatValidatorClientScript = @"
		<script language='javascript'>
		
		function {0}Validate(source, arguments)
		{{
			var sURL = ""{1}__serverSideRequest=true&__source="" + source.id;

			//add ControlToValidate
			if(source.controltovalidate != undefined)
			{{
				sURL += ""&ControlToValidateValue="" + document.all(source.controltovalidate).value;				
			}}
		
			var ControlsToValidate = source.ControlsToValidate;
			if(ControlsToValidate != undefined)
			{{
				var arrControlsToValidate = ControlsToValidate.split("";"");
				for(var i=0; i<arrControlsToValidate.length; i++)
				{{
					var Control = document.all(arrControlsToValidate[i]);
					if(Control) 
					{{
						sURL += ""&"" + Control.id + ""="" + Control.value;
					}}	
				}} 
			}}

			arguments.IsValid = (doXMLHTTPRequest(sURL) == ""true"");
		}}
		</script>";

		//variable keeps delimited by ';' string of Control ID's
		private string _ControlsToValidate;

		public string ControlsToValidate
		{
			get
			{
				return _ControlsToValidate;
			}
			set
			{
				_ControlsToValidate = value;
			}
		}

		protected override void OnPreRender(EventArgs e)
		{
			base.OnPreRender (e);
			//add ControlsToValidate as attribute
			//so it will be available at client
			if(ControlsToValidate != string.Empty) 
				this.Attributes.Add("ControlsToValidate", ControlsToValidate);   
			this.ClientValidationFunction = this.ID + "Validate";
			//use existed QueryString collection
			string Url = Page.Request.Url.ToString();
			if(Page.Request.QueryString.ToString() != string.Empty)
				Url += "&amp;";
			else
				Url += "?";
			Page.RegisterClientScriptBlock("GilatValidatorScript", string.Format(GilatValidatorClientScript, ID, Url));  
			if(!Page.IsClientScriptBlockRegistered("XMLHTTPRequestScript"))
			{
				Page.RegisterClientScriptBlock("XMLHTTPRequestScript", XMLHTTPRequestScript);
			}	
		}

		public event System.Web.UI.WebControls.ServerValidateEventHandler ClientValidate;

		/// <summary>
		/// overrides base event
		/// </summary>
		/// <PARAM name="e"></PARAM>
		protected override void OnLoad(EventArgs e)
		{
			base.OnLoad(e);
			//if this page called from client side validation
			//raise new event
			HttpRequest Request = this.Page.Request;

			if(Request.QueryString["__serverSideRequest"] == "true" &&
				Request.QueryString["__source"] == this.ID)
			{
				Page.Response.Clear();   
				ServerValidateEventArgs ServerValidateE = new ServerValidateEventArgs(Request.QueryString["ControlToValidateValue"], false);
				OnCallbackValidation(ServerValidateE); 
				if(ServerValidateE.IsValid)
					Page.Response.Write("true");   
				Page.Response.End(); 
			}
		}

		protected virtual void OnCallbackValidation(ServerValidateEventArgs e) 
		{     
			if (ClientValidate != null) 
			{
				ClientValidate(this, e);
			}  
		}

	}

}