.NET Framework Classes

Now that we ve covered a bit of the motivation behind the framework, let s take a deeper look at the classes. Classes in the .NET Framework are divided into logical groups called namespaces . Most classes in the .NET Framework exist under a top-level namespace known as System . The root System namespace contains the basic data types in the framework, such as numbers , Booleans, Uniform Resource Identifiers (URI), strings, and objects, the base type from which all other classes in the framework derive. System also contains a broad array of second-level namespaces that represent the core functionality in the framework, such as eventing , infrastructure, interfaces, attributes, and exceptions.

System.* Namespaces Overview

There are two general groups of classes in the .NET Framework: general-purpose base class libraries and application model “specific classes. It s useful to understand the difference between the two so that you ll better know when to use classes from each group as you build your application.

General-Purpose Class Libraries

General-purpose class libraries can be useful in almost any context. For example, System.String represents an immutable fixed-length string of Unicode characters . String manipulation is useful in a Web-based application that returns HTML content to the browser, a GUI client application that runs on the end user s computer, or a long-running service that has no graphical representation at all.

Table 1-1 contains System namespaces along with a brief description and an indication of whether the namespace represents a general-purpose base class library or is part of a particular application model. Each namespace contains anywhere from 10 to more than 100 classes, depending on the number of lower-level namespaces it contains.

Table 1-1: Second-Level System Namespaces*

Namespace	Description	Base Class or Application Model
CodeDom	Classes that can be used to reference the structure of a code document	Base
Collections	Contains interfaces and classes that define various collections of objects, such as lists, queues, bit arrays, hash tables, and dictionaries	Base
ComponentModel	Provides classes that are used to implement the run- time behavior of components and controls	Base
Configuration	Provides classes and interfaces that allow you to programmatically access .NET Framework configuration settings and handle errors in configuration files (.config files)	Base
Data	Contains the classes that represent ADO.NET, which enables you to build components that efficiently manage data	Base
Diagnostics	Provides classes that enable you to interact with system processes, event logs, and performance counters	Base
DirectoryServices	Provides easy access to Active Directory directory services from managed code	Base
Drawing	Provides access to GDI+ basic graphics functionality	Base
EnterpriseServices	Provides an important infrastructure for enterprise applications, including access to COM+	Base
Globalization	Contains classes that define culture- related information, including the language; the country/region; the calendars in use; the format patterns for dates, currency, and numbers; and the sort order for strings	Base
IO	Contains types that allow synchronous and asynchronous reading and writing on data streams and files	Base
Management	Provides access to a rich set of management information and management events about the system, devices, and applications designed for the Windows Management Instrumentation (WMI) infrastructure	Base
Messaging	Provides classes that allow you to connect to, monitor, and administer message queues on the network and send, receive, or peek messages	Base
Net	Provides access to network resources over protocols such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Hypertext Transfer Protocol (HTTP)	Base
Reflection	Contains classes and interfaces that provide a managed view of loaded types, methods , and fields, with the ability to dynamically create and invoke types	Base
Resources	Provides classes and interfaces that allow developers to create, store, and manage various culture-specific resources used in an application	Base
Runtime	Includes a broad set of third-level namespaces such as a Win32 interoperability layer, remoting, and object serialization	Base
Security	Provides the underlying structure of the CLR security system, including base classes for permissions	Base
ServiceProcess	Provides classes that allow you to implement, install, and control Windows service applications	Application model
Text	Contains classes representing ASCII, Unicode, UTF-7, and UTF-8 character encodings; abstract base classes for converting blocks of characters to and from blocks of bytes; and a helper class that manipulates and formats String objects without creating intermediate instances of String	Base
Threading	Provides classes and interfaces that enable multithreaded programming	Base
Timers	Provides classes that allow you to raise an event on a specified interval	Base
Web	Supplies classes and interfaces that enable the browser/ server communication used by ASP.NET	Application model
Windows.Forms	Contains classes for creating Windows-based applications that take full advantage of the rich user interface features available in the Microsoft Windows operating system	Application model
Xml	Provides standards-based support for processing XML	Base

*Based on the .NET Framework Class Library overview at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemNet.asp.

As you can tell from Table 1-1, the .NET Framework contains a broad set of functionality.

Application Model “Specific Classes

Think of an application model as a set of classes that define a manner in which an application operates. They define the general structure of the application. The following sections provide a brief look at the application models in the .NET Framework.

ASP.NET

ASP.NET, contained in the System.Web namespace, is designed to make it easy for developers to build real-world Web applications. It offers a rich application environment for building server-side HTTP applications that dynamically create content and send it to a client, such as a browser or a mobile device.

Using ASP.NET and the base class libraries in the framework designed for distributed application development, you can build applications that gather data from multiple back-end or remote sources and present it to the browser in an aggregated format. The following example demonstrates an ASP.NET page that calls an XML-based Web service using the .NET Framework.

This weather service sample application is extremely simple. It takes a postal code as an input parameter and returns the forecast. In this case, it always returns sunny unless the zip code supplied is 11111 , in which case it will say rainy , as shown in Figure 1-2. The following code listing shows the code for this application:

Weather Service Sample Application ”Visual Basic .NET

 <%@WebServiceLanguage="VB Class="WeatherService %> ImportsSystem ImportsSystem.Web.Services