vb.net: multiple inheritance in an interface

Question

I'm facing a problem regarding multiple inheritance in VB.net:

As far as I know VB.net does not support multiple inheritance in general but you can reach a kind of multiple inheritance by working with interfaces (using “Implements” instead of “Inherits”):

Public Class ClassName
    Implements BaseInterface1, BaseInterface2

End Class

That works fine for classes but I’d like to have an interface inheriting some base interfaces. Something like that:

Public Interface InterfaceName
    Implements BaseInterface1, BaseInterface2

End Interface

But the “Implements” keyword is not allowed for interfaces (what makes sense, of course). I tried to use a kind of abstract class which I know from Java:

Public MustInherit Class InterfaceName
    Implements BaseInterface1, BaseInterface2

End Class

But now I need to implement the defined methods from BaseInterface1 and BaseInterface2 within the InterfaceName class. But as InterfaceName should be an interface, too, I don’t want to have to implement these methods within that class.

In C# you can do that quite easy:

public interface InterfaceName: BaseInterface1, BaseInterface2 {}

Do you know if I can do something similar in VB.net?

Answer 1

Similar to Java, in VB.NET interfaces "extend" other interfaces. That means they "inherit" their functionality. They do not implement it.

Public Interface InterfaceName
    Inherits BaseInterface1, BaseInterface2
End Interface

Answer 2

Try

Public Interface InterfaceName
    Inherits BaseInterface1
    Inherits BaseInterface2
End Interface

Answer 3

A workaround is to have the abstract class (mustinherit) pass on the job of defining each item in the interface it does not want to implement with mustoverride. Try to predefine each one in a general sense if possible and make it overridable.

Answer 4

I would be careful when inheriting interfaces.

While it works, I have found that if you bind a BindingList(Of InterfaceName) to a BindingSource and the BindingSource to a DataGridView, then properties in Interface1 and Interface2 are not visible to the Visual Studio DataGridView designer for allocating as columns to the DataGridView.