C# 4 and .NET 4

1234 ❘ ChaPTer 41 Asp.net feAtures
using the ajaX library
There is a great deal of functionality available in the AJAX Library that you can use to further enhance your
web applications. However, to do this you need at least a working knowledge of JavaScript. In this section,
you see some of this functionality, although this is not an exhaustive tutorial.
The basic principles behind the use of the AJAX Library are much the same as for adding any type of clientside
script to a web application. You will still use the core JavaScript language, and you will still interact
with the DOM. However, there are many areas where the AJAX Library makes things easier for you.
This section explains many of these areas and provides a foundation that you can build on with further
experimentation and study of the online AJAX Library documentation.
The techniques covered in this section are illustrated in the PCSLibraryDemo project, which is referred to
throughout the rest of this chapter.
adding Javascript to a Web Page
The first thing you need to know is how to add client-side JavaScript to a web page. You have three
options here:
➤
➤
➤
Add JavaScript inline in ASP.NET web pages by using the element.
Add JavaScript to separate JavaScript files with the extension .js and reference these files from
elements or (preferably) by using the child element of the ScriptManager control.
Generate JavaScript from server-side code, such as code behind or custom extender controls.
Each of these techniques has its own benefits. For prototyping code, there is no substitute for inline code
because it is so quick and easy to use. You will also find it easy to associate client-side event handlers of
HTML elements and server controls with client-side functions, because everything is in the same file.
Having separate files is good for reusability, because you may create your own library of classes much like
the existing AJAX Library JavaScript files.
Generating code from code-behind can be tricky to implement because you will not usually have access to
IntelliSense for JavaScript programming when you use C# code. However, you will be able to generate code
dynamically in response to application state, and sometimes this is the only way to do things.
The extenders that you can create with the AJAX Control Toolkit include a separate JavaScript file that
you use to define behaviors, which gets around some of the problems of exposing client-side code from
the server.
In this chapter, you use the inline code technique, because it is simplest and allows you to concentrate on the
JavaScript functionality.
Global Utility functions
One of the features supplied by the AJAX Library that you will use most often is the set of global functions
that wrap other functionality. These include the following:
➤
➤
➤
$get() — This function enables you to get a reference to a DOM element by supplying its client-side
id value as a parameter, with an optional second parameter to specify the parent element to search in.
$create() — This function enables you to create objects and perform initialization at the same time.
You can supply between one and five parameters to this function. The first parameter is the type you
want to instantiate, which will typically be a type defined by the AJAX Library. The other parameters
enable you to specify initial property values, event handlers, references to other components, and the
DOM element that the object is attached to, respectively.
$addHandler() — This function provides a shorthand for adding an event handler to an object.
There are more global functions, but these are the ones you will use most often. $create() in particular is
a very useful way to reduce the amount of code required to create and initialize an object.
www.it-ebooks.info