C# 4 and .NET 4

asP.neT Web forms ❘ 1151
Conversely, web applications are compiled before being deployed to a web server, and don ’ t include .cs
fi le s . I n s t e ad , a pre - c ompi le d a s s e mbly i s deploye d to t he s er ver a long w it h A S P. N E T pa ge s .
In general, most ASP.NET programmers tend to prefer the web application model, and there are some
technologies (such as MVC) that will only work with web applications. Web sites are mainly useful in
the development stage, where quick changes to code may be required and a full deployment may not be
desirable.
state management in asP.neT
One of the key properties of ASP.NET pages is that they are effectively stateless. By default, no information
is stored on the server between user requests (although there are methods for doing this, as you will see later
in this chapter). At fi rst glance, this seems a little strange because state management is something that seems
essential for user - friendly interactive sessions. However, ASP.NET provides a workaround to this problem,
such that session management becomes almost transparent.
In short, information such as the state of controls on a Web Form (including data entered in text boxes
or selections from drop - down lists) is stored in a hidden viewstate fi eld that is part of the page generated
by the server and passed to the user. Subsequent actions, such as triggering events that require server - side
processing, such as submitting form data, result in this information being sent back to the server; this is
known as a postback operation. On the server, this information is used to repopulate the page object model
allowing you to operate on it as if the changes had been made locally.
You will see this in action shortly and examine the details.
asP.neT Web forms
As mentioned earlier, much of the functionality in ASP.NET is achieved using Web Forms. Before long,
you will dive in and create a simple Web Form to give you a starting point to explore this technology. First,
however, this section reviews some key points pertinent to Web Form design.
Note that some ASP.NET developers simply use a text editor such as Notepad to create fi les. We wouldn ’ t
advocate this ourselves because the benefi ts you get via an IDE, such as Visual Studio or Web Developer
Express are substantial, but it ’ s worth mentioning because it is a possibility. If you do take this route, you
have a great deal of fl exibility as to which parts of a web application you put where. This enables you, for
example, to combine all your code in one fi le. You can achieve this by enclosing code in elements,
using two attributes on the opening tag:
< script language="c#" runat="server" >
// Server-side code goes here.
< /script >
The runat= “ server ” attribute here is crucial because it instructs the ASP.NET engine to execute this code
on the server rather than sending it to the client, thus giving you access to the rich environment hinted at
earlier. You can place your functions, event handlers, and so on in server - side script blocks.
If you omit the runat= “ server ” attribute, you are effectively providing client - side code, which will fail if
it uses any of the server - side style coding that is discussed in this chapter. You can, however, use
elements to supply client - side script in languages such as JavaScript. For example:
< script language="JavaScript" type="text/JavaScript" >
// Client-side code goes here; you can also use "vbscript".
< /sc r i p t >
Note that the type attribute here is optional, but necessary if you want to comply with
HTML and XHTML standards.
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