INFO: How Visual Basic Classes Map to COM (259529)



The information in this article applies to:

  • Microsoft Visual Basic Professional Edition for Windows 6.0
  • Microsoft Visual Basic Enterprise Edition for Windows 6.0

This article was previously published under Q259529

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:

258827 Visual Basic Object Browser Cannot See the Default Interface


Modification Type:MajorLast Reviewed:1/11/2001
Keywords:kbDSupport kbinfo kbLocalSvr KB259529