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c#coclass

What does the C# CoClass attribute do?

I found code something like the following in a 3rd party library we're using.

[CoClass(typeof(BlahClass))]
public interface Blah : IBlah
{
}

What is this doing exactly? The msdn documentation didn't illuminate the subject sufficiently for me to follow.

Solution

  • It declares that the interface Blah is intended to be implemented by a specific class. It means that you can conveniently say new Blah and the runtime will know what object to create - something that is not normally possible with an interface.

    If you look at the generated declaration for BlahClass, it will presumably have a Guid associated with it which can be used to create an instance of a COM object.