C# 4 and .NET 4

What is ajax ❘ 1223
ConTrol
Timer
AsyncPostBackTrigger
desCriPTion
The ASP.NET AJAX Timer control is a useful way to cause an UpdatePanel
to update periodically. You can configure this control to trigger postbacks at
regular intervals. If this control is contained in an UpdatePanel control, then the
UpdatePanel will be updated every time the Timer control is triggered. This
control also has an associated event so that you can carry out periodic serverside
processing.
You can use this control to trigger UpdatePanel updates from controls that
aren’t contained in the UpdatePanel. For example, you can enable a drop-down
list elsewhere on a web page to cause an UpdatePanel containing a GridView
control to update.
The AJAX Extensions also include the ExtenderControl abstract base class for extending existing ASP.
NET server controls. This is used, for example, by various classes in the ASP.NET AJAX Control Toolkit,
as you will see shortly.
AJAX Library
The AJAX Library consists of JavaScript files that are used by client-side code in ASP.NET AJAX-enabled
web applications. There is a lot of functionality included in these JavaScript files, some of which is general
code that enhances the JavaScript language and some of which is specific to Ajax functionality. The AJAX
Library contains layers of functionality that are built on top of each other, as shown in the following table.
layer
Browser compatibility
Core services
Base class library
Networking
User interface
Controls
desCriPTion
The lowest-level code in the AJAX Library consists of code that maps various
JavaScript functionality according to the client web browser. This is necessary
because there are differences in the implementation of JavaScript in different
browsers. By providing this layer, JavaScript code in other layers does not have to
worry about browser compatibility, and you can write browser-neutral code that will
work in all client environments.
This layer contains the enhancements to the JavaScript language, in particular OOP
functionality. By using the code in this layer you can define namespaces, classes,
derived classes, and interfaces using JavaScript script files. This is of particular
interest to C# developers, because it makes writing JavaScript code much more like
writing .NET code (by using C# and encouraging reusability).
The client base class library (BCL) includes many JavaScript classes that provide lowlevel
functionality to classes further down the AJAX Library hierarchy. Most of these
classes are not intended to be used directly.
Classes in the networking layer enable client-side code to call server-side code
asynchronously. This layer includes the basic framework for making a call to a
URL and responding to the result in a callback function. For the most part, this is
also functionality that you will not use directly; instead, you will use classes that
wrap this functionality. This layer also contains classes for JSON serialization and
deserialization. You will find most of the networking classes on the client-side Sys.
Net namespace.
This layer contains classes that abstract user interface elements such as HTML
elements and DOM events. You can use the properties and methods of this layer to
write language-neutral JavaScript code to manipulate web pages from the client. User
interface classes are contained in the Sys.UI namespace.
The final layer of the AJAX Library contains the highest-level code, which provides
Ajax behaviors and server control functionality. This includes dynamically
generated code that you can use, for example, to call Web services from client-side
JavaScript code.
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