Beginning ASP.NET 4.5 in CSharp and VB Opsylum

184 x CHAPTER 5 PROGRAMMING YOUR ASP.NET WEB PAGES
Organizing Code with Namespaces
Namespaces seem to cause a lot of confusion with new developers. They think they’re scary, they
think way too many of them exist, or they don’t see the need to use them. None of this is true, and
with a short explanation of them, you’ll understand and maybe even like namespaces.
Namespaces are intended to solve two major problems: to organize the enormous amount of functionality
in the .NET Framework and in your own code, and to avoid name collisions, where two
different types share the same name. One common misconception about namespaces is that there is
a direct relation with .NET assemblies (files with a .dll extension that are loaded and used by the
.NET Framework), but that’s not the case. Although you typically find namespaces like System
.Web.UI in a DLL called System.Web.dll, it’s possible (and common) to have multiple namespaces
defined in a single DLL or to have a namespace be spread out over multiple assemblies. Keep that in
mind when adding references to assemblies, as explained later.
To see what a namespace looks like, open one of the Code Behind files of the ASPX pages you’ve
created so far. You’ll see something similar to this:
VB.NET
Partial Class Demos_CalculatorDemo
Inherits System.Web.UI.Page
C#
public partial class Demos_CalculatorDemo : System.Web.UI.Page
{
Note that the definition of the class name is followed by the Inherits keyword in VB and a colon in
C#, which in turn are followed by System.Web.UI.Page. You see later what this Inherits keyword
is used for. In this code, Page is the name of a class (a data type), which is defined in the System
.Web.UI namespace. By placing the Page class in the System.Web.UI namespace, developers (and
compilers) can see this class is about a web page. By contrast, imagine the following (fictitious) class
name:
Microsoft.Word.Document.Page
This code also refers to a Page class. However, because it’s placed in the Microsoft.Word
.Document namespace, it’s easy to see that it’s referring to a page of a Word document, not a web
page. This way there is no ambiguity between a web page and a Word document page. This in turn
helps the compiler understand which class you are referring to.
Another benefit of namespaces is that they help you find the right data type. Instead of displaying
thousands and thousands of items in the IntelliSense list, you get a few top-level namespaces. When
you choose an item from that list and press the dot key (.), you get another relatively short list with
types and other namespaces that live inside the chosen namespace.
Namespaces are nothing more than simple containers that you can refer to by name using the dot
notation. They are used to prefix each data type that is available in your application. For example,
the Double data type lives in the System namespace, thus its fully qualified name is System
.Double. Likewise, the Button control you’ve added to your web pages lives in the System.Web
.UI.WebControls namespace, thus its full name is System.Web.UI.WebControls.Button.