Question

I am making an interface that has a number of events defined in it. When I implement the interface in a class the events will show up. I want to force a class that implements my interface to also have to make the event handlers too. I don’t care where the class raises the event, but I want them to have to define what happens once the event is raised. Is this possible and if so, how do I do it?

Answer 1

Since interface define contracts rather than implementation, there’s not really a way to “force” implementations to behave in a certain way.

That being said, I’m a little bit confused when you mention event handler within the same class as the event. Unless I’m confusing some terminology, the handlers are the methods that belong to the subscriber of the event, not the publisher. By this, do you mean something like an “On<Event>” method? If you need to expose those to something outside the class, then those can be added to the interface as well, but it would be up to the implementing class to know to tie the two together, and it seems like a somewhat peculiar design.

If you’re looking to force some sort of behaviour like this, would something like a {abstract} base class suit your needs better than an interface?

(ETA: You may also consider looking at the Observer pattern?)