ASP.NET AJAX

ASP.NET AJAX is a set of extensions to ASP.NET developed by Microsoft for implementing Ajax functionality.

Road Map

In its early development stages, ASP.NET AJAX was given the code name Atlas. Initial releases were made public to the development community in the form of CTPs (Community Technical Previews). The production version, ASP.NET AJAX 1.0 RTM; was released on January 23, 2007 as an extension to ASP.NET 2.0.

Important release milestones for ASP.NET AJAX are as follows:

• CTPs - October, December 2005, January, March, April, June, July 2006
• Beta - October, November 2006
• Release Candidate (RC) - December 2006
• ASP.NET AJAX 1.0 RTM - January 23, 2007
• ASP.NET AJAX 3.5 - November 19, 2007 (as part of ASP.NET 3.5)

The next version, ASP.NET AJAX 4.0; will be part of the ASP.NET 4.0 framework release.

Browser support

ASP.NET AJAX runs on the following browsers:

• Microsoft Internet Explorer (>= 6.0)
• Mozilla Firefox (>= 1.5)
• Opera (>= 9.0)
• Apple Safari (>= 2.0)
• Google Chrome

ASP.NET AJAX Suite

At present, the ASP.NET AJAX suite consists of the following components and packages:

• Microsoft Ajax Library 3.5, which is a JavaScript library that provides the client-side features of the ASP.NET AJAX framework. Integrated in ASP.NET 3.5, the library is also available as a separate download for use in other environments, such as PHP.
• A server framework – included in ASP.NET 3.5 – for building Ajax-enabled ASP.NET server controls. These components are also available for ASP.NET 2.0 in a separate package called ASP.NET 1.0 Extensions.
• ASP.NET 2.0 AJAX Templates, a package with a set of Visual Studio templates for building ASP.NET AJAX applications with ASP.NET 2.0 and Visual Studio 2008.
• ASP.NET AJAX Preview, a package with the new features that will be part of the future versions of the framework.

Microsoft Ajax Library

The Microsoft Ajax Library is a JavaScript library that provides the features for the client portion of the ASP.NET AJAX framework.

• Components. The library provides an infrastructure to build either visual or non-visual JavaScript components. A global JavaScript object – Sys.Application – is responsible for managing the lifecycle of client components.
• JavaScript extensions – An enhanced type system is introduced to emulate object-oriented constructs such as namespaces, classes and interfaces; and to perform reflection on client types.
• Abstraction API – Common operations on the DOM (retrieving elements, setting styles and other manipulations) are automatically translated by the library into browser-specific calls.
• Ajax – A set of client components is provided to handle Ajax requests and web-service calls.
• Application Services – The library allows accessing the ASP.NET Membership, Authentication, Roles and Profile services from the client side.

Recently, new features have been announced as part of the ASP.NET AJAX 4.0 release:

• Template Engine – Allows displaying data on the client side by using HTML templates and a custom binding notation. This approach avoids to perform page rendering on the server side.
• Declarative instantiation of client components – Allows registration, instantiation and configuration of client components using markup code, without writing any imperative JavaScript code.
• Live Bindings – Synchronize element properties.

The UpdatePanel Control

The UpdatePanel is an ASP.NET server control that updates portions of a web page without reloading it. Through a mechanism called asynchronous postback, the HTML for the region of the page wrapped by the control is sent by the server asynchronously through an Ajax request.

The ASP.NET controls that have been specified as content in an UpdatePanel are able to cause either synchronous (traditional) or asynchronous postbacks, by means of triggers.

A trigger is an event coming from an ASP.NET control that causes an UpdatePanel to refresh its contents. Through triggers, an asynchronous postback can be started also by controls that are declared outside the region of the ASP.NET page wrapped by the UpdatePanel control.

In the following code, only the content of the UpdatePanel control (the span element that displays the current date and time) is re-rendered every time the button is clicked.

<asp:Button ID="Button1" runat="server" Text="Refresh" />

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
   <Triggers>
      <asp:AsyncPostBackTrigger ControlID="Button1" EventName="Click" />
   </Triggers>
   <ContentTemplate>
      <span><%= DateTime.Now %></span>
   </ContentTemplate>
</asp:UpdatePanel>

Script Controls and Extenders

The server portion of the ASP.NET AJAX framework introduces two categories of ASP.NET server controls for adding client capabilities to server controls.

An Extender is used to add client functionality to an existing ASP.NET control, without the need to create a new server control.

A Script Control is a standalone ASP.NET control that offers both server and client functionality.

See also

• Ajax framework
• ASP.NET

External links

• ASP.NET AJAX (formerly "Atlas")
• Atlas At Last : ASP.NET Atlas Powers the AJAX-Style Sites You’ve Been Waiting For
• Microsoft Atlas Mini-Guide from SearchVB.com - Registration Required
• Ajax Tools for ASP.NET Developers
• ASP.NET AJAX Articles selection
• AJAX Control Toolkit