C# 4 and .NET 4

1222 ❘ ChaPTer 41 Asp.net feAtures
AJAX Extensions
ASP.NET AJAX functionality is contained in two assemblies that are installed in the GAC:
➤
➤
System.Web.Extensions.dll — This assembly contains the ASP.NET AJAX functionality, including
the AJAX Extensions and the AJAX Library JavaScript files, which are available through the
ScriptManager component (which is described shortly).
System.Web.Extensions.Design.dll — This assembly contains ASP.NET Designer components
for the AJAX Extensions server controls. This is used by the ASP.NET Designer in Visual Studio or
Visual web developer.
Much of the AJAX Extensions component of ASP.NET AJAX is concerned with enabling partial-page
postbacks and JSON serialization for Web services. This includes various HTTP handler components and
extensions to the existing ASP.NET Framework. All this functionality can be configured through the web.
config file for a web site. There are also classes and attributes that you can use for additional configuration.
However, most of this configuration is transparent, and you will rarely need to change the defaults.
Your main interaction with AJAX Extensions will be using server controls to add Ajax functionality to your
web applications. There are several of these, which you can use to enhance your applications in various
ways. The following table shows a selection of the server-side components. You see these components in
action later in this chapter.
ConTrol
ScriptManager
UpdatePanel
UpdateProgress
desCriPTion
This control is central to ASP.NET AJAX functionality and is required on every
page that uses partial-page postbacks. Its main purpose is to manage clientside
references to the AJAX Library JavaScript files, which are served from the
ASP.NET AJAX assembly. The AJAX Library is used extensively by the AJAX
Extensions server controls, which all generate their own client-side code.
This control is also responsible for the configuration of Web services that you
intend to access from client-side code. By supplying Web service information
to the ScriptManager control, you can generate client-side and serverside
classes to manage asynchronous communication with Web services
transparently.
You can also use the ScriptManager control to maintain references to your own
JavaScript files.
The UpdatePanel control is an extremely useful one and is perhaps the ASP.
NET AJAX control that you will use most often. This control acts like a standard
ASP.NET placeholder and can contain any other controls. More important, it
also marks a section of a page as a region that can be updated independently of
the rest of the page, in a partial-page postback.
Any controls contained by an UpdatePanel control that cause a postback
(a Button control, for example) will not cause full-page postbacks. Instead,
they cause partial-page postbacks that will update only the contents of the
UpdatePanel.
In many situations, this control is all you need to implement Ajax functionality. For
example, you can place a GridView control in an UpdatePanel control, and any
pagination, sorting, and other postback functionality of the control will take place
in a partial-page postback.
This control enables you to provide feedback to users when a partial page
postback is in progress. You can supply a template for this control that will be
displayed when an UpdatePanel is updating. For example, you could use a
floating control to display a message such as “Updating...” so that the
user is aware that the application is busy. Note that partial-page postbacks do
not interfere with the rest of a web page, which will remain responsive.
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