In the previous chapter, you saw how to use C# to create Windows applications; in this chapter, you’ll see how to use C# to create applications for the Web.
The .NET technology for building web applications (and dynamic web
sites) is ASP. NET 2.0, which provides a rich collection of types for
building web applications in its System.Web and System.Web.UI namespaces. There is a great deal
to learn about ASP.NET, but much of it is language-independent. ASP.NET
offers a rich suite of controls and related tools, including tools to
validate data, display dates, present advertisements, interact with users,
and so forth. Most of these require no coding whatsoever.
Tip
For more on the details of ASP.NET, please see Programming ASP.NET, Third Edition, by Jesse Liberty and Dan Hurwitz (O’Reilly, 2005).
The role of the C# programmer in ASP.NET development is to write the event handlers that respond to user interaction. Many of the event handlers will either add data to a database or retrieve data and make it available to the controls.
With Web Forms , the application is deployed to a web server, and users interact with the application through a standard browser.
Web Forms bring Rapid Application Development (RAD ) techniques (such as those used in Windows Forms) to the development of web applications. As with Windows Forms, you drag-and-drop controls onto a form and write the supporting code either inline or in code-behind pages.
Tip
ASP.NET 2.0 Web Forms are the successor to the enormously successful ASP.NET 1.x Web Forms, which in turn were the successor to ASP pages.
The goal of ASP.NET 2.0 was to reduce the amount of coding by 70 percent compared to ASP 1.x. This means that web programming is increasingly declarative rather than programmatic—that is, you declare controls on your Web Form rather than writing (and rewriting) boiler-plate code.
You still have the option of writing code (you can always write code), but for the vast majority of web programming, you’ll write a lot less code with ASP.NET 2.0 than you did with 1.x.
Web Forms implement a programming model in which web pages are dynamically generated on a web server for delivery to a browser over the Internet. With Web Forms, you create an ASPX page with more or less static content consisting of HTML and Web Controls, and you write C# code to add additional dynamic content. The C# code runs on the server, and the data produced is integrated with the declared objects on your page to create an HTML page that is sent to the browser.
There are three critical points to pick up from the previous paragraph, and which you should keep in mind for this entire chapter:
Web pages can have both HTML and Web Controls (described later).
All processing is done on the server (you can have client-side processing with scripting languages, but that isn’t part of ASP.NET).
If you use ASP.NET Web Controls, what the browser sees is just HTML (there is an exception to this; with those browsers that Microsoft defines as “uplevel,” some script may be sent as well).
In short, Web Forms are designed to be viewed through any browser, with the server generating the correct browser-compliant HTML. Just as with Windows Forms, you can create Web Forms in Notepad (or another editor of your choice) rather than in Visual Studio, but it makes no sense to do so and we will continue to use Visual Studio 2005 to enhance productivity and reduce errors.
Web Forms divide the user interface into two parts: the visual part or user interface (UI), and the logic that lies behind it. This is very similar to developing Windows Forms, as shown in Chapter 18. This is called code separation ; all examples in this book use code separation, though it is possible to write the C# code in the same file with the user interface.
Tip
In Version 2.0 of ASP.NET, Visual Studio takes advantage of partial classes, allowing the code-separation page to be far simpler than it was in 1.x. Because the code-separation and declarative pages are part of the same class, there is no longer a need to have protected variables to reference the controls of the page, and the designer can hide its initialization code in a separate file.
The UI page is stored in a file with the extension .aspx. When you run the form, the server
generates HTML sent to the client browser. This code uses the rich Web
Forms types found in the System.Web and System.Web.UI namespaces of the .NET Framework
Class Library (FCL ).
With Visual Studio, Web Forms programming couldn’t be simpler: open a form, drag some controls onto it, and write the code to handle events . Presto! You’ve written a web application.
On the other hand, even with Visual Studio, writing a robust and complete web application can be a daunting task; Web Forms offer a very rich UI and the number and complexity of Web Controls have greatly multiplied in recent years. User expectations about the look and feel of web applications have risen accordingly.
In addition, web applications are inherently distributed. Typically, the client will not be in the same building as the server. For most web applications, you must take network latency, bandwidth, and network server performance into account when creating the UI; a round trip from client to host might take a few seconds.