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   ► KBProgrammingVB ClassicOOP   Print This    All Groups  
  From the January 2016 Issue of Prestwood eMag
 
VB Classic OOP:
VB Classic Interfaces
 
Posted 11 years ago on 10/24/2008 and updated 2/21/2009
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KB101442

General Info: Interface

An element of coding where you define a common set of properties and methods for use with the design of two or more classes.

Both interfaces and abstract classes are types of abstraction. With interfaces, like abstract classes, you cannot provide any implementation. However, unlike abstract classes, interfaces are not based on inheritance. You can apply an Interface to any class in your class tree. In a real sense, interfaces are a technique for designing horizontally in a class hierarchy (as opposed to inheritance where you design vertically). Using interfaces in your class design allows your system to evolve without breaking existing code.

VB Classic Interfaces

VB6 has limited support for interfaces. You can create an interface of abstract methods and properties and then implement them in one or more descendant classes. It's a single level implementation though (you cannot inherit beyond that). The parent interface class is a pure abstract class (all methods and properites are abstract, you cannot implement any of them in the parent class).

In the single level descendant class, you have to implement all methods and properties and you cannot add any. Your first line of code is Implements InterfaceName.

Default Interface Visibility: Friend

If you do not specify an interfaces visibility, the default is Friend but an interface's members are always public -- which makes sense but is noteworthy.

More Info

Definition:  Interface

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