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Originally published at Internet.comWhat difference a year or two can bring. Two and a half years ago I thought I'd be writing a book titled Visual Basic 7 Unleashed for Sams. Completing the final drafts of Sams Visual Basic .NET Unleashed reminds me that a lot has changed in Visual Basic.
To help you make the transition as thoroughly and as completely as possible myself and other authors and contributors are writing a lot about threading, reflection, assemblies, COM interop, and delegates. But, reviewing programming subjects with a friend recently, I was reminded that there are developers at all levels, not just the advanced level. To be as thorough as possible, then, I am exploring advanced topics as well as non-advanced topics. (I welcome queries from readers too, and sometimes write an article based on several queries.)
This article is to the point. In this article we will examine interfaces: how to define them and how to implement them.
The idea of an interface is not new to COM, but in Visual Basic 6 every class was a COM interface. In Visual Basic .NET every class is a class and an interface is an interface, but not a COM interface. Classes have existed for decades and interfaces are not the sole purview of COM. A class describes the fields, properties, events, and methods a type will have. An interface is more like a portal or an attachment. An interface says that a type will implement these specific methods, but does not define what a type is. For example, a house can have a Window but so can a car. A type that implements a method open could be defined as something that has a Window, but the types could define cars, boats, houses, or the soul...
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