C# Tutorial - The .NET Framework Class Library (FCL)

The .NET Framework Class Library is a comprehensive collection of pre-written object-oriented classes, known as objects, which you can use to develop any application. These objects make it easy to rapidly develop applications as a lot of the nitty-gritty work is done for you, allowing the developer to concentrate on developing the application rather than having to worry about the small tasks such as getting buttons to work etc.

These classes make it easy to write applications for both the web and windows based applications. Each platform has its own set of reusable classes that handle a variety of specialized development scenarios.

In essence, these classes can be grouped into several categories that provide a diverse array of software services.

  • Core functionality such as interaction with basic data types and collections; input/output for files, networks and console; other runtime facilities.

  • Interacting with databases, XML support and tabulation/tree-structured data.

  • Support for web based applications with a server side event model.

  • Support for windows based desktop applications, including GUI and GDI+.

  • Building SOAP-based XML web services.

The FCL includes more than 3500 classes for use with .NET. Not all classes are used by every language, for example, Visual Basic has many classes which are not used by the other Microsoft languages.

You can also get more information about the .NET framework by visiting Microsoft at http://msdn2.microsoft.com/en-gb/netframework/default.aspx.

Putting It All Together

To give a better overview of the .NET Framework, the next diagram shows how the .NET Framework fits in context with the applications you develop and the operating system.

We can often think of software as working in layers, the operating system interfaces with the hardware, working with device drivers etc to make the computer work. The .NET Framework sits on top of this, providing a common interface between the operating system and any application written in .NET.

Layers of The .NET Framework

Overview of the .NET Framework Layers

  • .NET applications do not access the operating system or hardware directly. Instead the use the services of the .NET Framework to achieve this.

  • The .NET Framework Class Library is a collection of pre-written classes that can be used to create applications to run on the windows platform or web pages.

  • The Common Language Runtime (CLR) is the foundation of the .NET Framework. It is the part of the system that runs and manages .NET code at runtime. The CLR converts the Intermediate Language into native code that can be run on the operating system.

  • The Common Type System defines the data types used by all of the .NET languages.

  • The Intermediate Language is stored as an assembly with a reference to the classes that the application requires. The assembly is simply an executable file that has an .exe or .dll extension.

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