Primary Interop Assembly

In the COM programming model, once a GUID is assigned to a type, the GUID always refers to that specific type no matter where the type appears. For example, a common interface might be defined in many different type libraries, but each separate type library would have to define the interface with the same GUID, so the duplication is not a problem. However, if you generate COM Interop assemblies for these separate type libraries, a new and distinct assembly would be created for each type library. Each of these separate assemblies would contain distinct types (as far as the CLR is concerned). The strong identity and self-describing nature of .NET assemblies is actually working against you in this case. Here, it is leading to a GAC that is cluttered with interop assemblies that all contain RCWs for the same type library. Worse yet, to the CLR each assembly contains distinct and incompatible types, because each one has a different strong name.

To avoid this proliferation of assemblies and potential type incompatibilities, the framework gives you the ability to designate one assembly as the primary interop assembly for a type library. A primary interop assembly is always signed with a strong name, by the original publisher of the type library.

Project Management Made Easy

Project Management Made Easy

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