Events of a non-delegate type

Question

I've implemented a class that looks like this interface:

[ImmutableObject(true)]
public interface ICustomEvent
{
    void Invoke(object sender, EventArgs e);

    ICustomEvent Combine(EventHandler handler);
    ICustomEvent Remove(EventHandler handler);

    ICustomEvent Combine(ICustomEvent other);
    ICustomEvent Remove(ICustomEvent other);
}

This CustomEvent class works much like a MulticastDelegate. It can invoked. It can be combined with another CustomEvent. And a CustomEvent can be removed from another CustomEvent.

Now, I want to declare a class like this:

class EventProvider
{
    public event CustomEvent MyEvent;

    private void OnMyEvent()
    {
        var myEvent = this.MyEvent;
        if (myEvent != null) myEvent.Invoke(this, EventArgs.Empty);
    }
}

Unfortunately, this code does not compile. A Compiler Error CS0066 appears:

'EventProvider.MyEvent': event must be of a delegate type

Basically, what I need is a property that has add and remove accessors instead of get and set. I think the only way to have that is using the event keyword. I know that one obvious alternative is to declare two methods that would do the adding and removing, but I want to avoid that too.

Does anybody knows if there is a nice solution this problem? I wonder if there is any way to cheat the compiler to accept a non-delegate type as an event. A custom attribute, perhaps.

By the way, someone asked a similar question in experts-exchange.com. Since that site is not free, I can't see the responses. Here is the topic: http://www.experts-exchange.com/Programming/Languages/C_Sharp/Q_21697455.html

Answer 1

Try this:

CustomEvent myEvent

public event EventHandler MyEvent {
    add { myEvent = myEvent.Combine(value); }
    remove {myEvent = myEvent.Remove(value); }
}

You can add and remove normal EventHandler delegates to it, and it will execute the add and remove accessors.

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EDIT: You can find a weak event implementation here.
2^nd EDIT: Or here.