Introduction to ASP.NET and Web Forms
An important part of .NET is its use in creating Web applications through a technology known as ASP.NET. Far more than an incremental enhancement to Active Server Pages (ASP), the new technology is a unified Web development platform that greatly simplifies the implementation of sophisticated Web applications. In this chapter we introduce the fundamentals of ASP.NET and cover Web Forms, which make it easy to develop interactive Web sites. In Chapter 15 we cover Web services, which enable the development of collaborative Web applications that span heterogeneous systems.
What Is ASP.NET?
We begin our exploration of ASP.NET by looking at a very simple Web application. Along the way we will establish a testbed for ASP.NET programming, and we will review some of the fundamentals of Web processing. Our little example will reveal some of the challenges in developing Web applications, and we can then appreciate the features and benefits of ASP.NET, which we will elaborate in the rest of the chapter.
Web Application Fundamentals
A Web application consists of document and code pages in various formats. The simplest kind of document is a static HTML page, which contains information that will be formatted and displayed by a Web browser. An HTML page may also contain hyperlinks to other HTML pages. A hyperlink (or just link) contains an address, or a Uniform Resource Locator (URL), specifying where the target document is located. The resulting combination of content and links is sometimes called hypertext and provides easy navigation to a vast amount of information on the World Wide Web.
SETTING UP THE WEB EXAMPLES
As usual, all the example programs for this chapter are in the chapter folder. To run the examples, you will need to have Internet Information Services (IIS) installed on your system. IIS is installed by default with Windows 2000 Server. You will have to explicitly install it with Windows 2000 Workstation. Once installed, you can access the documentation on IIS through Internet Explorer via the URL http://localhost, which will redirect you to the starting IIS documentation page, as illustrated in Figure 141.
Figure 14-1 Internet Information Services documentation
The management tool for IIS is a Microsoft Management Console (MMC) snap-in, the Internet Services Manager, which you can find under Administrative Tools in the Control Panel. Figure 142 shows the main window of the Internet Services Manager. You can start and stop the Web server and perform other tasks by right-clicking on Default Web Site. Choosing Properties from the context menu will let you perform a number of configurations on the Web server.
The default home directory for publishing Web files is \Inet-pub\wwwroot on the drive where Windows is installed. You can change this home directory using Internet Services Manager. You can access Web pages stored at any location on your hard drive by creating a virtual directory. The easiest way to create one is from Windows Explorer. Right-click over the desired directory, choose Sharing..., select the Web Sharing tab, click on the Add button, and enter the desired alias, which will be the name of the virtual directory. Figure 143 illustrates creating an alias Chap14, or virtual directory, for the folder \OI\NetVb\Chap14. You should perform this operation now on your own system in order that you may follow along as the chapter's examples are discussed.
Figure 14-2 Internet Services Manager
Figure 14-3 Creating a virtual directory
ASP.NET and Web Forms
Once a virtual directory has been created, you can access files in it by including the virtual directory in the path of the URL. In particular, you can access the file default.htm using the URL http://localhost/Chap14/. The file default.htm contains a home page for all the ASP.NET example programs for this chapter. See Figure 144.
Figure 14-4 Ome page for ASP.NET example programs
An Echo Program
The first example program for this chapter is Hello.aspx, shown as a link on the home page. The example is complete in one file and contains 