INFO: How Visual Basic Classes Map to COM

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This article was previously published under Q259529

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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.

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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.

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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 (http://support.microsoft.com/kb/258827/EN-US/ ) Visual Basic Object Browser Cannot See the Default Interface

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