Introducing the Framework Class Library (FCL) to Visual Basic Developers
This article is excerpted from Chapter 4, "Introduction to the .NET Framework Class Library," from Visual Basic Programmer's Guide to the .NET Framework Class Library by Lars Powers and Mike Snell (0672322323). It assumes prior experience with versions of Visual Basic, but no knowledge of the .NET Framework. This material is based on the Beta 2 release version of Microsoft's .NET Technology.
As you probably figured out from its name, the class library is merely a collection of classes and related structures that can be leveraged as base building blocks for application development. As such, you can think of this collection of classes as an API: the classes are a boundary interface between our applications and the operating system. This concept, of course, is really nothing new to Visual Basic developers: the ADO library, the Win32 API, the COM+ services libraryall of these constructs have allowed us to reference and use pre-existing code in our applications. The class library is a massive library of pre-existing code that you, as a Visual Basic programmer, can use as a foundation for your application features.
Referencing pre-existing libraries of code traditionally has been pretty easy with Visual Basic. One of the main issues, however, was that many times these code libraries weren't initially consumable by Visual Basic developers. If you were a C++ programmer, the world was open to you in terms of functionality. VB programmers had to wait for Microsoft or some other entity to make a wrapper or interface available that we could use from VB. Documentation also tended to be a problem.
Following is a brief introduction to the ways you can expect to leverage the FCL in your development.