Question

This is .NET 4.0/C#. I have a class that inherits from an interface:

public class DocumentModel : IDocumentObject
{
     //this is not in the interface and wont ever be
     public void NewMethod(){//my code}
}

In my DocumentModel class, I added a public method that is not a part of the interface. When I call it,

var doc = new DocumentModel();
doc.NewMethod();

I get the following:

Error 30 ‘IDocumentObject’ does not contain a definition for ‘NewMethod’ and no
extension method ‘NewMethod’ accepting a first argument of type ‘IDocumentObject’

How do I add a method to my class that’s not in the interface? Thanks

Answer 1

In the interface add the method declaration.

public interface IDocumentObject
{
void NewMethod();
}

Or if you do not want it in the interface, you’ll have to create an instance of the class of the type of the class, not the type of interface.

DocumentModel doc = new DocumentModel();