ASP.NET.in.a.Nutshell.Second.Edition [Electronic resources] نسخه متنی

Chapter 23. The System.Web Namespace

The System.Web namespace contains some of the
fundamental ingredients for ASP.NET applications. These ingredients
include the classes used for the original built-in ASP objects
(Request, Response,
Application, and Server), as
well as classes for managing cookies, configuring page caching,
implementing tracing, and retrieving information about the web server
and client browser. Aside from the classes required for web services
and the Web Forms user interface, the System.Web
namespace contains the heart of ASP.NET's
functionality. Figure 23-1 and Figure 23-2 show the types in this namespace.

One confusing aspect about the System.Web
namespace is Microsoft's "all roads
lead to Rome" approach to backward compatibility.
For example, the HttpRequest class can be accessed
on a Web Form through the Page class
(Page.Request), the HttpContext
class (Page.Context.Request), and the
HttpApplication class
(Page.Context.ApplicationInstance.Request). In all
cases, the reference is pointing to the same object. Essentially, the
HttpContext class encapsulates the fundamental
types that relate to an HTTP request. The
HttpContext object is made available to all
IHttpModule and IHttpHandler
instances (which includes HttpApplication,
System.Web.UI.Page, and
System.Web.UI.UserControl), and some of its
properties are "magically" copied
into these classes for convenience and backward compatibility. When
you use the built-in Request object on a Web Forms
page, for example, you use the Request property
from the Page class. Generally, using the
Page properties is the easiest and least expensive
way to access the built-in objects.

Due to backward compatibility, some class names don't match
the name of the corresponding built-in object. For example, the
Application object is an instance of the
HttpApplicationState class, not the
HttpApplication class. Similarly, the built-in
Response.Cache object references an instance of
the HttpCachePolicy class, while the built-in
Cache object references the
System.Web.Caching.Cache class.

Figure 23-1. Fundamental types from System.Web

Figure 23-2. More System.Web types, including collections and exceptions