Using the Ajax.NET Framework

What developer wants to spend hours manually writing Ajax plumbing when the Ajax.NET framework does this for free? The Ajax.NET Framework presents a remarkably easy-to-use framework that will simplify Ajax development and allow developers to spend more time on implementation details and less time on parsing XML.

What Is Ajax?

If Ajax is still a new concept for you, Ajax stands for Asynchronous JavaScript and XML. Ajax groups these technologies and provides a break from the traditional model requiring a post back to the server in order to run server-side methods. Ajax allows a browser to make calls to server-side code and receive a response from the server all without using the ASP.NET postback, which transfers full ViewState and page information with each request.

How Does Ajax Work?

The “magic” of Ajax lies in the use of the HttpRequest object to facilitate communication between the browser and the server. This object will contact the server, call the designated code and wait for a response from the server. The nice part about this system is that since the processing is asynchronous, the Web browser will continue to allow the user to keep working uninterrupted with the Web application all while continuing to process on the server.

A very simplistic way to think about this technology is to say that in one respect Ajax grants the user the ability to call code-behind methods from JavaScript.

Call Backs

Ajax will request a service from the server and wait for a response. The way Ajax applications wait for the response is what makes the applications useful. Once you have sent the request to the server for processing, the browser will continue to do its work. Once the server generates a response the browser will recognize that response and then continue processing.

You have two options available to you when calling code on the server in an Ajax environment. You may choose to define a callback method or you may choose to simply send a message to the server and allow the application to continue with its work without being notified the operation is complete.

If you choose to recognize the response, you will define a callback method in JavaScript. A callback method runs once the browser has recognized a response from the server. Once the callback method is invoked, the application may now conduct some additional processing of the response data as provided by the server.

Implications of N-Tiered Development

Some of the traditional lines of n-tier application architecture may blur when you use Ajax. In an application where you use Ajax but you haven’t thought through the architecture, you might have a considerable amount of overlap of business logic in the user interface layer.

You want to make sure you keep your architect’s hat on while developing Ajax applications. Remember that the business layer should know nothing of how to display information to the user and the user interface should not contain business rules. To accomplish this goal, you should strictly return data to the user interface layer and allow UI services to format the data for the final presentation. An Ajax developer may need to use an interim layer between the business objects and the browser to further prepare server-side data before rendering to the browser.

By: Craig Shoemaker

Craig Shoemaker is a software engineer for PDSA, Inc. (www.pdsa.com), a Microsoft Partner in Southern California. With over 10 years experience in Web development, he brings a unique perspective to tying together front- and back-end development. Craig is also the host of the Polymorphic Podcast, (www.polymorphicpodcast.com), a weekly audio show about object-oriented development, architecture, and best practices in .NET. You may reach Craig at craigs@pdsa.com.

craigs@pdsa.com