Question

I understand the benefits of events using delegate types with signature delegate void delegate_name(object sender, EventArgs e)

a) But besides the fact that it may save us some typing, are there any other reasons why we should use already defined delegate types EventHandler/EventHandler<T> instead of declaring our own delegate types with signature delegate void delegate_name(object sender, EventArgs e)?

b) Two other reason I can think of for using the predefined delegate types EventArgs/EventArgs<T> are:

• people consuming particular event ( say event EventHandler my_event ) will immediately know how to use that event?

• perhaps some popular third party methods accept as parameters EventHandler/ EventHandler<T> delegate types, and thus if there’s any chance that our code may use those third party methods, we should use predefined delegates EventHandler/Eventhandler<T>?

thank you

Answer 1

To me, the question is a little strange. What would be the benefit of doing this otherwise (defining delegate types that exactly match EventHandler<TEventArgs> for some TEventArgs)?

That said, there is at least one benefit I can think of to doing it the “normal” way: certain APIs already expect to deal with EventHandler<TEventArgs> delegates; for example, Rx Extensions includes a method that looks like this:

Observable.FromEvent<TEventArgs>(
    Action<EventHandler<TEventArgs>> addHandler,
    Action<EventHandler<TEventArgs>> removeHandler
);

If you defined your own delegate, using methods like this — which expect EventHandler<TEventArgs> delegates — would become more complicated than necessary for no added benefit (that I can see, anyway).