ASP.NET improves on the type of application that developers could use in classic ASP, and adds a new application, called a webservice. Read this article to learn more about the new application, which lets clients use the functionality of a particular application without needing to use the application's specific user interface. The article is excerpted from chapter two of
by G. Andrew Duthie. (O'Reilly, 2003, ISBN: 0596005202).
Application Types In classic ASP, there was really only one type of application—one in which a client accessed a page with the .asp extension and in which that page, either through embedded VBScript or JScript or through script in combination with components built on Microsoft’s COM standard, returned HTML to the browser to form the user interface with which the client would interact. Clients typically interacted with the application only through this user interface and did not have the option of creating their own alternative interface to the functionality exposed by the application.
ASP.NET provides an enhanced version of this type of application, which we’ll discuss in the next section. ASP.NET also introduces a new type of application, called a webservice, which provides clients the ability to use functionality exposed by an application without being tied into that application’s user interface implementation.
ASP.NET Web Applications The ASP.NET Web Application is the type of application most developers will work with on a regular basis. The terminology comes from the description used in the Visual Studio .NET environment to describe the project type used to create this type of application. You may also hear this type of application described as an ASP.NET Web Forms Application. For reasons we’ll explore in the next chapter, we prefer the former term.
An ASP.NET Web Application, in its simplest form, consists of a directory made available via HTTP using the IIS administration tool or through the Web Sharing tabof a folder’s Properties dialog (or by creating a webapplication project in Visual Studio .NET) and at least one ASP.NET page, designated by the .aspx file extension. This file (or files), whose structure we’ll discuss in detail in the next chapter, typically contains a mix of HTML and server-side code. This HTML and server-side code combine to create the final output of the page, typically consisting of HTML markup that is sent to the client browser. A simple ASP.NET page is shown in Example 2-1.
Example 2-1 . A simple ASP.NET page
<%@ Page Language="VB" %>
<html>
<head>
<title>Simple ASP.NET Page</title>
<script runat="server">
Sub Page_Load()
Message.Text = "Hello, world!"
End Sub
</script>
</head>
<body>
<asp:Label id="Message" Runat="server"/>
</body>
</html>
The page shown in Example 2-1 simply executes the code appearing in the <script runat="server">, which uses an ASP.NET Label control to display some text, along with the standard HTML tags that are contained in the file. Figure 2-1 shows the output of the page as viewed in Notepad by using the View Source option in Internet Explorer. In this case, the Page_Load method (actually an event handler, which we’ll discuss more in later chapters) sets the Text property of an ASP.NET Label control to “Hello, world!”. Because the Label control will render its Text property to the browser automatically, “Hello, world!” will appear in the output that is sent to the browser, as shown in Figure 2-1.
The key to understanding how ASP.NET Web Applications work is understanding that the code in a <script runat="server"> block (or a <% %> render block) is executed on the server—after the client requests the page, but before the output of the page request is sent to the client browser. This allows developers to decide, based on the code they write and the input received from the user, just what output actually is sent to the browser, either directly (such as by calling the Write method of the Response object) or by manipulating controls, as shown in Example 2-1. It also allows additional functionality, such as server-side state management, to be provided to these applications.
Figure 2-1. Output of a simple ASP.NET page (source view)
Web Forms and Web Controls Example 2-1 uses a control called the Label control to output text to the browser. This control is an example of what are referred to as Web Controls. Web Controls (also referred to as Server Controls), which are discussed in detail in Chapter 5, are compiled classes that run on the server and provide functionality similar to that of Windows controls such as textboxes, dropdown lists, etc. The key is that these controls run at the server, and so can be manipulated programmatically in server-side code. WebForm is a term used to describe an .aspxfile that makes use of Web Controls. |
Besides the containing directory and ASP.NET file(s), an ASP.NET Web Application may also contain configuration files ( web.config ), User Control files ( .ascx ), and an application settings file ( Global.asax ), as well as code-behind, assembly, and class files that provide additional functionality to the application. We’ll discuss each of these file types later in this chapter.
 This chapter is from ASP.NET in a Nutshell, by G. Andrew Duthie. (O'Reilly, 2003, ISBN: 0596005202). Check it out at your favorite bookstore today. Buy this book now.
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