Building ASP.NET Pages
In this article, you learn how to build basic ASP.NET Web Forms Pages. Don't let the Forms part of the name mislead you. Web Forms Pages can do much more than display standard HTML forms. Most, if not all, the pages of your ASP.NET application will be Web Forms Pages, which enable you to create pages with interactive, dynamic, or database-driven content.
Web Forms Pages are pieced together out of two building blocks. First, you assemble the dynamic portion of the user interface by using ASP.NET controls. ASP.NET controls enable you to display "smart" HTML forms, for example, and present interactive grids of database data. The first part of this article provides an overview of all the ASP.NET controls.
The second building block of a Web Forms Page is the application logic, which includes the code that executes when you click a form button or the code that retrieves the database data displayed within a control. In the second part of this article, you learn how to add application logic to your Web Forms Pages to handle both control and page events.
Finally, in the last part of this article, you are formally introduced to the structure of an ASP.NET Web Forms Page. You learn about the different sections of a Web Forms Page and the type of content appropriate to each section.
After reading this article, you can start creating dynamic Web sites by building interactive, dynamic pages using ASP.NET controls and handling control and page events with application logic.
ASP.NET and the .NET Framework
ASP.NET is part of Microsoft's overall .NET framework, which contains a vast set of programming classes designed to satisfy any conceivable programming need. In the following two sections, you learn how ASP.NET fits within the .NET framework, and you learn about the languages you can use in your ASP.NET pages.
The .NET Framework Class Library
Imagine that you are Microsoft. Imagine that you have to support multiple programming languagessuch as Visual Basic, JScript, and C++. A great deal of the functionality of these programming languages overlaps. For example, for each language, you would have to include methods for accessing the file system, working with databases, and manipulating strings.
Furthermore, these languages contain similar programming constructs. Every language, for example, can represent loops and conditionals. Even though the syntax of a conditional written in Visual Basic differs from the syntax of a conditional written in C++, the programming function is the same.
Finally, most programming languages have similar variable data types. In most languages, you have some means of representing strings and integers, for example. The maximum and minimum size of an integer might depend on the language, but the basic data type is the same.
Maintaining all this functionality for multiple languages requires a lot of work. Why keep reinventing the wheel? Wouldn't it be easier to create all this functionality once and use it for every language?
The .NET Framework Class Library does exactly that. It consists of a vast set of classes designed to satisfy any conceivable programming need. For example, the .NET framework contains classes for handling database access, working with the file system, manipulating text, and generating graphics. In addition, it contains more specialized classes for performing tasks such as working with regular expressions and handling network protocols.
The .NET framework, furthermore, contains classes that represent all the basic variable data types such as strings, integers, bytes, characters, and arrays.
Most importantly, for purposes of this book, the .NET Framework Class Library contains classes for building ASP.NET pages. You need to understand, however, that you can access any of the .NET framework classes when you are building your ASP.NET pages.
As you might guess, the .NET framework is huge. It contains thousands of classes (over 3,400). Fortunately, the classes are not simply jumbled together. The classes of the .NET framework are organized into a hierarchy of namespaces.
In previous versions of Active Server Pages, you had access to only five standard classes (the Response, Request, Session, Application, and Server objects). ASP.NET, in contrast, provides you with access to over 3,400 classes!
A namespace is a logical grouping of classes. For example, all the classes that relate to working with the file system are gathered together into the System.IO namespace.
The namespaces are organized into a hierarchy (a logical tree). At the root of the tree is the System namespace. This namespace contains all the classes for the base data types, such as strings and arrays. It also contains classes for working with random numbers and dates and times.
You can uniquely identify any class in the .NET framework by using the full namespace of the class. For example, to uniquely refer to the class that represents a file system file (the File class), you would use the following:
System.IO refers to the namespace, and File refers to the particular class.
You can view all the namespaces of the standard classes in the .NET Framework Class Library by viewing the Reference Documentation for the .NET Framework.
Standard ASP.NET Namespaces
The classes contained in a select number of namespaces are available in your ASP.NET pages by default. (You must explicitly import other namespaces.) These default namespaces contain classes that you use most often in your ASP.NET applications:
SystemContains all the base data types and other useful classes such as those related to generating random numbers and working with dates and times
System.CollectionsContains classes for working with standard collection types such as hash tables, and array lists
System.Collections.SpecializedContains classes that represent specialized collections such as linked lists and string collections
System.ConfigurationContains classes for working with configuration files (Web.config files)
System.TextContains classes for encoding, decoding, and manipulating the contents of strings
System.Text.RegularExpressionsContains classes for performing regular expression match and replace operations.
System.WebContains the basic classes for working with the World Wide Web, including classes for representing browser requests and server responses
System.Web.CachingContains classes used for caching the content of pages and classes for performing custom caching operations
System.Web.SecurityContains classes for implementing authentication and authorization such as Forms and Passport authentication
System.Web.SessionStateContains classes for implementing session state
System.Web.UIContains the basic classes used in building the user interface of ASP.NET pages
System.Web.UI.HTMLControlsContains the classes for the HTML controls
System.Web.UI.WebControlsContains the classes for the Web controls
.NET Framework-Compatible Languages
Dozens of other languages created by companies other than Microsoft have been developed to work with the .NET Framework. Some examples of these other languages include Python, SmallTalk, Eiffel, and COBOL. This means that you could, if you really wanted to, write ASP.NET pages using COBOL.
Regardless of the language that you use to develop your ASP.NET pages, you need to understand that ASP.NET pages are compiled before they are executed. This means that ASP.NET pages can execute very fast.
The first time you request an ASP.NET page, the page is compiled into a .NET class, and the resulting class file is saved beneath a special directory on your server named Temporary ASP.NET Files. For each and every ASP.NET page, a corresponding class file appears in the Temporary ASP.NET Files directory. Whenever you request the same ASP.NET page in the future, the corresponding class file is executed.
When an ASP.NET page is compiled, it is not compiled directly into machine code. Instead, it is compiled into an intermediate-level language called Microsoft Intermediate Language (MSIL). All .NET-compatible languages are compiled into this intermediate language.
An ASP.NET page isn't compiled into native machine code until it is actually requested by a browser. At that point, the class file contained in the Temporary ASP.NET Files directory is compiled with the .NET framework Just in Time (JIT) compiler and executed.
The magical aspect of this whole process is that it happens automatically in the background. All you have to do is create a text file with the source code for your ASP.NET page, and the .NET framework handles all the hard work of converting it into compiled code for you.
What about VBScript? Before ASP.NET, VBScript was the most popular language for developing Active Server Pages.
ASP.NET does not support VBScript, and this is good news. Visual Basic is a superset of VBScript, which means that Visual Basic has all the functionality of VBScript and more. So, you have a richer set of functions and statements with Visual Basic.
Furthermore, unlike VBScript, Visual Basic is a compiled language. This means that if you use Visual Basic to rewrite the same code that you wrote with VBScript, you can get better performance.
If you have worked only with VBScript and not Visual Basic in the past, don't worry. Since VBScript is so closely related to Visual Basic, you'll find it easy to transition between the two languages.
Microsoft includes an interesting tool named the IL Disassembler (ILDASM) with the .NET framework. You can use this tool to view the disassembled code for any of the ASP.NET classes in the Temporary ASP.NET Files directory. It lists all the methods and properties of the class and enables you to view the intermediate-level code.
This tool also works with all the ASP.NET controls discussed in this article. For example, you can use the IL Disassembler to view the intermediate-level code for the TextBox control (located in a file named System.Web.dll).