This document discusses AJAX (Asynchronous JavaScript and XML) and how it can be used in ASP.NET. It defines AJAX as a technique for building interactive web applications that can retrieve data from the server asynchronously without interfering with the display and behavior of the existing page. It provides an overview of how AJAX works, demonstrates its use in ASP.NET 1.x and 2.0, discusses challenges and things to watch out for, and introduces the Atlas library from Microsoft for AJAX in ASP.NET 2.0 applications.

1. AJAX in ASP.NET
James Crowley
Developer Fusion
http://www.developerfusion.co.uk/

2. Overview
 What is AJAX?
 How does it work?
 Using it in ASP.NET 1.x
 Using it in ASP.NET 2.0
 Pros & Cons

3. What is AJAX (and who cares?)
 Current postback solutions can be slow
and confusing to users
 AJAX allows server-side processing to
occur without a postback, and therefore...
a more interactive & responsive UI
 Nothing new, but all the rage thanks to
Google Maps, Flickr, and A9 to name a
few

4. How it works
Server
Web Server
Database
Client Browser
JavaScript
DHTML
XML HTTP
Object
1
Async HTTP Request

5. How it works
Server
Web Server
Database
Client Browser
JavaScript
DHTML
XML HTTP
Object
2

6. How it works
Server
Web Server
Database
Client Browser
JavaScript
DHTML
XML HTTP
Object
3
Async HTTP Response

7. AJAX in ASP.NET 1.x
 Either we deal with the XML HTTP
request ourselves
 or we can use an existing library, such as
AJAX.NET wrapper
http://ajax.schwarz-interactive.de/
“My AJAX.NET”
http://jason.diamond.name/weblog/

8. Demo
 “Colourizing” Code

9. Complex Data Types
 Need to either reproduce (a subset of) the
.NET type system within JavaScript or
vice-versa
 Need to serialize for transfer via HTTP
 Serializable return types dealt with
automatically
 Parameters are harder

10. Demo
 “Google Suggest”

11. AJAX in ASP.NET 2.0
 Known as “Script Callbacks”
 Call ClientScript.GetCallBackEventReference to
get the string for a javascript call to trigger a
callback
 Implement the ICallbackEventHandler interface
public interface ICallbackEventHandler {
void RaiseCallbackEvent(string eventArgument);
String GetCallbackResult();
}
public string GetCallbackEventReference(System.Web.UI.Control control,
string argument, string clientCallback,
string context, string clientErrorCallback, bool useAsync)

12. ASP.NET 2.0 vs AJAX.NET
 No dynamic mapping of parameters using
reflection
 More complicated with multiple callbacks
 No JavaScript objects corresponding to
server-side types (only returning strings)
 Executes within the page lifecycle

13. Things to note
 ViewState not updated during a callback
because of allowance for parallel callbacks
 Page.IsPostBack is true for callbacks and
postbacks. Use Page.IsCallback
 Request.Browser.SupportsCallback

14. Demo
 AJAX in ASP.NET 2.0

15. Atlas
 New library from Microsoft to plug-in to
ASP.NET 2.0
 Preview available from http://atlas.asp.net/
 Warning: Not yet even Beta quality!
 But Microsoft wants your feedback…

16. Atlas
 Cross-browser script libraries
 Callbacks can be triggered in same way as
AJAX.NET library
 Web Services integration
 Declarative data binding
 New AJAX-enabled server controls

17. Things to watch out for…
 Debugging is a pain
 Response timeouts and server exceptions
 Non-JavaScript/non-ActiveX scenarios

18. Things to watch out for…
 Accessibility, page flow, scroll position
 Can break layered architectures
 Inability to access by URL, and breaking
back/forward browser buttons
 No search indexing for AJAX’ed data

19. Wrapping Up
 More work for us
 But… fast interactive UI for the user
 Any questions?

20. References
 ASP.NET AJAX Libraries
 http://ajax.schwarz-interactive.de/ (AJAX.NET)
 Tutorial @ http://www.developerfusion.co.uk/show/4704/
 http://jason.diamond.name/weblog/ (My AJAX.NET)
 http://atlas.asp.net/ (Atlas)
 My Contact Details
 Web: http://www.developerfusion.co.uk/
 Email: james@developerfusion.co.uk