C# – Automation Error in VB 6.0 from a C# class

c++com-interopvb6

I have created a C# class library and I am using it through a VB 6.0 application. But when I try to call any method (which returns a string) it gives me an automation error. The C# class is running fine otherwise.

Any idea why?

Best Solution

As fbinder says, you should strong sign your assembly, and use some attributes. The attributes we use (successfully) are:

[ComVisible( true )]
[ClassInterface( ClassInterfaceType.None )]
[Guid( "00000000-0000-0000-0000-000000000000" )]
[ComDefaultInterface( typeof( IExposedClass ) )]
public class ExposedClass : IExposedClass
{
    //need a parameterless constructor - could use the default
    public ExposedClass() { }

    public string GetThing()
    {
        return "blah";
    }
}

[ComVisible( true )]
[Guid( "00000000-0000-0000-0000-000000000000" )]
[InterfaceType( ComInterfaceType.InterfaceIsIUnknown )]
public interface IExposedClass
{
    string GetThing();
}