I've been merrily writing events using custom delegate types and the generic Action
delegate type, without really thinking about what I was doing.
I have some nice extension helpers for Action
and EventHandler
which makes me tend to use those predefined delegate types rather than my own, but aside from that...
Is there a good reason other than convention to favour EventHandler
and EventHandler<T>
over custom delegate types or generic Action
delegate types?
The main advantage of the signature EventHandler<T>
over using one parameter for each member of your EventArgs
is that you can add additional properties to your EventArgs
without breaking compatibility.
IMO this is the most important argument. Being able to extent your EventArgs
without breaking subscribing code is very nice. But of course you can achieve the same with any signature that uses some kind of property-bag parameter instead of a parameter per property.
Then there is variance, EventHandler<Base>
is convertible to EventHander<Derived>
, so you can write an EventHandler with parameter EventArgs
and it can subscribe to events which have more specific EventArgs
.
Extension methods are another plus, but you already mentioned that.
No, no good reason.
If your events do not require EventArgs
or a sender
object, then you don't need to use EventHandler
or EventHandler<T>
.
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