Magic AJAX: Applying AJAX to your existing Web Pages

using System;
using System.Web;

namespace Ajax
{
	/// <summary>
	/// Includes the CallBack event, Context, Request and Response, for convenience.
	/// </summary>
	/// <remarks>
	/// Inhering from AjaxPage is not required to apply AJAX on your pages. You can
	/// implement the ICallBackEventHandler on your page to handle the CallBack event, and
	/// use the HttpContext.Current, CallBackHelper.Request and CallBackHelper.Response
	/// properties.
	/// 
	/// You cannot use the Context, Request and Response of the System.Web.UI.Page
	/// because, during a CallBack, the Context of the page is invalid. If you don't want
	/// to replace the Page.Request and Page.Response from your code for
	/// CallBackHelper.Request and CallBackHelper.Response, and your page is inherited
	/// from System.Web.UI.Page, you can use AjaxPage for convenience.
	/// </remarks>
	public class AjaxPage : System.Web.UI.Page, ICallBackEventHandler
	{
		/// <summary>
		/// Raised by AjaxHttpModule when a CallBack occurs
		/// </summary>
		public event EventHandler CallBack;

		/// <summary>
		/// The base Page Request property doesn't work during a CallBack. Use this instead.
		/// </summary>
		public new HttpRequest Request
		{
			get
			{
				return Context.Request;
			}
		}

		/// <summary>
		/// The base Page Response property doesn't work during a CallBack. Use this instead.
		/// </summary>
		public new HttpResponse Response
		{
			get
			{
				return Context.Response;
			}
		}

		/// <summary>
		/// Raises the CallBack event.
		/// </summary>
		/// <remarks>
		/// Called by AjaxHttpModule.
		/// </remarks>
		public void RaiseCallBackEvent()
		{
			OnCallBack (EventArgs.Empty);
		}

		protected override HttpContext Context
		{
			get
			{
				return HttpContext.Current;
			}
		}

		protected virtual void OnCallBack(EventArgs e)
		{
			if (CallBack != null)
				CallBack(this, e);
		}
	}
}