Q259529: INFO: How Visual Basic Classes Map to COM

Article: Q259529
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbCOMt kbLocalSvr kbVBp kbVBp600 kbGrpDSVB kbDSupport
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Professional Edition for Windows, version 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 
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SUMMARY
=======

Every Component Object Model (COM) object must implement at least one interface.
Visual Basic simplifies this concept by creating a default interface that can be
created automatically for each class. Visual Basic also hides the name of the
default interface.

MORE INFORMATION
================

For a class module, Class1, Visual Basic creates a hidden interface named
_Class1 as a default. When you use the OLEVIEW tool to look at the compiled
Visual Basic components' type library, you can see that Visual Basic creates a
CoClass named Class1, which implements _Class1 as the default interface. The
Visual Basic components' type library looks like the following:

  [
     hidden,
     ...
  ]
  interface _Class1 {
     ...
  }
  coclass Class1 {
     [default] interface _Class1;
  };

You can create a Class1 object like the following:

  Dim myObject as Class1
  set myObject = new Class1
  ' then call myObject's any public methods...

The variable myObject of type Class1 is transparently cast to the _Class1
reference by the Visual Basic Compiler (because clients only use interface
references to access COM objects.) Using Class1 as an alias for the _Class1
interface makes it very easy to create a COM-compliant object in Visual Basic.

REFERENCES
==========

For additional information regarding implementing a COM interface in Visual
Basic, click the article number below to view the article in the Microsoft
Knowledge Base:

  Q258827 Visual Basic Object Browser Cannot See the Default Interface

Additional query words:

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Keywords          : kbCOMt kbLocalSvr kbVBp kbVBp600 kbGrpDSVB kbDSupport 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVBA600 kbVB600
Version           : WINDOWS:6.0
Issue type        : kbinfo

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