Question

I’m trying to achieve something like this

public abstract class BaseEvent
{
    public abstract void Dispatch(IEventHandler handler);
}

public class MyEvent : BaseEvent
{
    public override void Dispatch(IMyEventHandler handler)
    {
        handler.OnMyEvent(this);
    }
}

public interface IEventHandler
{
}

public interface IMyEventHandler : IEventHandler
{
    void OnMyEvent(MyEvent e);
}

The problem is that the compiler complains saying that MyEvent doesn’t implement BaseEvent since Dispatch is taking an IMyEventHandler instead of an IEventHandler. I don’t want to let MyEvent.Dispatch take a IEventHandler then cast it to a IMyEventHandler because I would like compile time checks to make sure I’m not doing something stupid like passing in some other type of event handler. I found a possible solution (below) but I’m wondering if there is a nicer way of doing this.

public abstract class BaseEvent<H> where H : IEventHandler
{
    public abstract void Dispatch(H handler);
}

public class MyFirstEvent<H> : BaseEvent<H> where H : IMyFirstEventHandler
{
    public override void Dispatch(H handler)
    {
        handler.OnMyFirstEvent(this);
    }
}

public interface IEventHandler
{
}

public interface IMyFirstEventHandler : IEventHandler
{
    void OnMyFirstEvent<H>(MyFirstEvent<H> e) where H : IMyFirstEventHandler;
}

Thanks, Tom

Answer 1

I’ve used your approach before.

It looks pretty solid to me.