C# 4 and .NET 4

1186 ❘ ChaPTer 41 Asp.net feAtures
Finally, in the largest section of this chapter, you look at ASP.NET AJAX. This technology is a powerful
way to enhance the user experience. It enables web sites and applications to become more responsive
by updating sections of a page independently, as well as streamlining the process of adding client-side
functionality.
Throughout much of this chapter, you will refer to a large example web site that includes all the techniques
that you have seen in this and the previous chapter. This web site, PCSDemoSite, is available for download
(along with the other code for this chapter) at www.wrox.com. The relevant sections of code are examined as
necessary, and the additional code (mostly dummy content or simple code you have already seen) is left for
you to examine at your convenience.
user and CusTom ConTrols
Sometimes, a given control doesn’t quite work as you would like it to, or perhaps one section of code,
intended for reuse on several pages, is too complex in the hands of multiple developers. In such cases, there
is a strong argument for building your own controls.
The .NET Framework provides an ideal setting for the creation of custom controls, using simple
programming techniques. Every aspect of ASP.NET server controls is exposed for you to customize,
including such capabilities as templating and client-side scripting. However, there is no need to write code
for all these eventualities; simpler controls can be a lot easier to create.
In addition, the dynamic discovery of assemblies that is inherent in a .NET system makes installation of
web sites and applications on a new web server as simple as copying the directory structure containing
your code. To make use of the controls you have created, you simply copy the assemblies containing those
controls along with the rest of the code. You can even place frequently used controls in an assembly located
in the global assembly cache (GAC) on the web server, so that all web sites and applications on the server
have access to them.
This chapter discusses two different kinds of controls:
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User controls and how to convert existing ASP.NET pages into controls
Custom controls and how to group the functionality of several controls, extend existing controls, and
create new controls from scratch
User controls are illustrated with a simple control that displays a card suit (club, diamond, heart, or spade),
so that you can embed it in other ASP.NET pages with ease. We won’t go into too much depth for custom
controls, although we show you the basic principles and direct you to more information beyond this book.
user Controls
User controls are controls that you create using ASP.NET code, just as you use in standard ASP.NET
web pages. The difference is that after you have created a user control you can reuse it in multiple
ASP.NET pages.
For example, say that you have created a page that displays some information from a database, perhaps
information about an order. Instead of creating a fixed page that does this, you can to place the relevant
code into a user control, and then insert that control into as many different web pages as you want.
In addition, you can define properties and methods for user controls. For example, you can specify a
property for the background color for displaying your database table in a web page, or a method to re-run a
database query to check for changes.
To start, you create a simple user control.
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