Question

I have a basic doubt. Internally how are events represented as methods or as (fields)objects. If event is a field then how one can still contain events in the interface definition.

Thanks
JeeZ

Answer 1

If you type this:

public event EventHandler MyEvent;

what the compiler generates is (simplified) this:

// declares a normal delegate of type 'EventHandler'
private EventHandler _myEvent;

// declares 'add_MyEvent' and 'remove_MyEvent' methods similar to a property
public event EventHandler MyEvent {
    add { _myEvent += value; }
    remove { _myEvent -= value; }
}

An event is similar to a property; a wrapper around a delegate that only allows methods to be added or removed. This is so you can’t completely re-assign the delegate and delete other people’s subscriptions to it.

All you are doing when specifying an event in an interface is that any implementing classes should have the add and remove methods for the event. Very similar to declaring a property on an interface, in fact.

This is also why you can only call or re-assign the event in the class it is declared in – any references to the MyEvent event within the class are re-routed to use the delegate directly, whereas outside the class you can only access the add and remove methods, not the delegate directly.