Advanced COM Programming with Visual Basic 6'0

1
Chapter 4

• Advanced COM Programming with Visual Basic 6.0
• Lesson 1 Creating Custom Interfaces

2
Learning Objectives

• Explain how interface-based programming
  relates to component-based software development.
• Describe the role of interfaces in COM.
• Define default interfaces and their purpose.
• Describe the benefits of creating custom
  interfaces.

3
Interface-based programming

• Interface-based programming is a concept
  created by the computer science academia and
  companies that needed to develop enterprise
  software and information systems.
• It defines two separate but related elements an
  interface and a coclass.
• An interface is a data type that contains
  definitions of public methods without containing
  any code.
• The coclass contains the code for the methods
  defined by the interface.

4
Interface pointers

• COM provides the ability for objects to
  communicate with each other both in-process and
  out-of-process. Interface pointers achieve this
  communication. When a client application calls a
  method of a COM object, the client points to a
  location in memory where the COM objects
  interface resides.

5
Interfaces and VB

• In VB, you can simply create class modules
  within an ActiveDLL project, and VB creates the
  interfaces and coclasses for you.
• When you develop COM components such as ActiveX
  DLL projects with VB, public creatable class
  modules are translated into coclasses in the type
  library (.tlb file) of the components. In
  addition, a default interface is created
  automatically and is assigned the same name as
  the class module with an undersoce(_) prefix.

6
View a Type Library with the OLE View Tool

• To create a COM DLL.