Use of VB.NET class in VB6 via interop requires class to have constructor?

Question

When I try to create a VB.NET object via interop in VB6, I have noticed I get this error if my VB.NET class doesn't have a constructor:

Error 430 - Class doesn't support automation

All I have to do is put an empty constructor in the VB.NET class, eg:

Public Sub New()

End Sub

and the error is avoided. Is this the expected behaviour?

Yes. Com classes being wrapped in C# must have a parameterless constructor. This restriction travels both ways. — Joel Etherton
– Joel Etherton, Commented Nov 15, 2012 at 14:02

Hans Passant · Accepted Answer · 2012-11-15 14:53:19Z

2

VB6 creates objects through COM, using the class factory for a COM coclass. The underlying method is IClassFactory::CreateInstance(). This method does not permit passing any arguments to the factory. It therefore follows that the [ComVisible] .NET class must have a constructor that doesn't take any arguments.

.NET already creates a default constructor for a class, unless you specify a constructor yourself that takes arguments. Which will never be used, you might as well remove it. Now you also don't need the empty default constructor anymore.

answered Nov 15, 2012 at 14:53

Hans Passant

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1 Comment

CJ7 Over a year ago

I have found that I get the above error if I have no constructor. The only way it seems to work is if a parameterless constructor is put in.

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