Transcript AJAX in ASP.NET - developer Fusion

AJAX in ASP.NET
James Crowley
Developer Fusion
http://www.developerfusion.co.uk/
Overview
What is AJAX?
 How does it work?
 Using it in ASP.NET 1.x
 Using it in ASP.NET 2.0
 Challenges

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

How it works
1
Client Browser
Server
Async HTTP Request
JavaScript
DHTML
XML HTTP
Object
Web Server
Parameters
Database
How it works
2
Client Browser
JavaScript
DHTML
Server
XML HTTP
Object
Web Server
Database
How it works
3
Client Browser
Server
Async HTTP Response
JavaScript
DHTML
XML HTTP
Object
Web Server
Text, XML, HTML, etc
Database
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/
Demo

“Colourizing” Code
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

Demo

“Google Suggest”
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
public string GetCallbackEventReference(System.Web.UI.Control control,
string argument, string clientCallback,
string context, string clientErrorCallback, bool useAsync)

Implement the ICallbackEventHandler interface
public interface ICallbackEventHandler {
void RaiseCallbackEvent(string eventArgument);
String GetCallbackResult();
}
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

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

Demo

AJAX in ASP.NET 2.0
Atlas
New library from Microsoft to plug-in to
ASP.NET 2.0
 Preview available from http://atlas.asp.net/
 Warning: pre-Alpha quality!
 But Microsoft wants your feedback…

Atlas
Cross-browser script libraries, bringing
namespaces, inheritance, and plenty more
 Callbacks triggered in similar way to
AJAX.NET library
 Web Services integration
 Declarative data binding
 New AJAX-enabled server controls

Things to watch out for…
Debugging is a pain
 Response timeouts and server exceptions
 Non-JavaScript/non-ActiveX scenarios

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

Wrapping Up
AJAX enables you to create web apps that are…
more responsive
with enhanced functionality
… and a great user experience
Go away and experiment!
 Email me: [email protected]

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/
 http://atlas.asp.net/

(My AJAX.NET)
(Atlas)
My Contact Details
 Web:
http://www.developerfusion.co.uk/
 Email: [email protected]