C#•3y ago

❔ C# EventArgs

I'm starting to use System.EventHandler events and I'm just wondering if there is a point to the EventArgs class other than to be inherited for custom args? Like, I'm calling

StartEvent?.Invoke(this, new EventArgs());

StartEvent?.Invoke(this, new EventArgs());

and the

new EventArgs()

new EventArgs()

just seems kind of pointless since its empty. Can I send something through the default EventArgs with a lambda expression or something?

canton7•3/10/23, 4:53 PM

You can use to avoid an allocation

canton7•3/10/23, 4:53 PM

But yeah, it's just there so you can add some args in the future without breaking backwards compat

PacrombieOP•3/10/23, 4:53 PM

And to add those args, you have to make a class deriving from EventArgs?

Thinker•3/10/23, 4:55 PM

What is the event?

PacrombieOP•3/10/23, 4:56 PM

I have these guys

Thinker•3/10/23, 4:56 PM

So you own the event?

PacrombieOP•3/10/23, 4:56 PM

Yes

Thinker•3/10/23, 4:57 PM

Really you shouldn't be using just plain EventArgs

PacrombieOP•3/10/23, 4:57 PM

If I don't want to send any args, just use EventArgs.Empty like the other person said?

PacrombieOP•3/10/23, 4:58 PM

And if I do want to send args, make a class deriving from EventArgs with the values I need?

Thinker•3/10/23, 4:58 PM

If the event doesn't need any args then the type of the event should be

PacrombieOP•3/10/23, 4:58 PM

Thinker•3/10/23, 4:58 PM

If you need args, you should use

PacrombieOP•3/10/23, 4:59 PM

With s, can you still reference the sender in the functions added to it?

Thinker•3/10/23, 4:59 PM

Well you can add that as an argument

PacrombieOP•3/10/23, 4:59 PM

PacrombieOP•3/10/23, 5:00 PM

Like this?

Thinker•3/10/23, 5:00 PM

What's the point of passing an as the sender?

Thinker•3/10/23, 5:01 PM

Do the subscribers actually need to do anything with the sender?

PacrombieOP•3/10/23, 5:02 PM

So a is invoking these events and I want the to be able to update with these values with when the event fires. I send the sender with the event so that the subscribers can get the public values they need.

PacrombieOP•3/10/23, 5:02 PM

(The subscribes some of its update functions to the ability events)

PacrombieOP•3/10/23, 5:03 PM

Would this be a better choice then?

PacrombieOP•3/10/23, 5:03 PM

Since the sender would only ever be a PlayerAbility?

Thinker•3/10/23, 5:13 PM

yeah

Thinker•3/10/23, 5:14 PM

Generally having to cast an EventArgs to the appropriate derived type and having the sender as an object is just bad

PacrombieOP•3/10/23, 5:14 PM

Yeah that's what I've been doing and it just feels bad

PacrombieOP•3/10/23, 5:15 PM

Thank you for your help :)

canton7•3/10/23, 5:57 PM

Eh, the standard advice isn't to use Action etc for events. That's very rare

canton7•3/10/23, 5:57 PM

The thing with using EventHandler is that you can add extra args layer without breaking backwards compat. That's why all of Microsoft's events use the event args pattern

canton7•3/10/23, 5:58 PM

And yes, so add your own args, make your own EventArgs subclass

Anton•3/10/23, 6:46 PM

If you pass things by or , use a delegate type

Ccanton7 And yes, so add your own args, make your own EventArgs subclass

Thinker•3/10/23, 6:55 PM

Although you shouldn't pass just

canton7•3/10/23, 7:15 PM

Why not? That's why EventHandler and EventArgs.Empty exist, and for exactly the same reason: so that you can add args without a breaking change

Thinker•3/10/23, 7:16 PM

Well you have to cast them, which is inherently not very safe

canton7•3/10/23, 7:16 PM

No you don't?

Thinker•3/10/23, 7:17 PM

I mean a type deriving from EventArgs sure, not just plain EventArgs

canton7•3/10/23, 7:18 PM

I don't get the confusion. If you have an EventHandler event and a subscriber which takes EventArgs, you can update the event to be an EventHander<T> without breaking the subscriber, and later update the subscriber to take that EventArgs subclass

canton7•3/10/23, 7:18 PM

No casting required

Thinker•3/10/23, 7:20 PM

This is of course assuming the subscriber doesn't do anything with the args

Thinker•3/10/23, 7:20 PM

There's no reason not to use EventHandler<T> from the start

canton7•3/10/23, 7:21 PM

EventArgs<T>? That's not a thing

TThinker This is of course assuming the subscriber doesn't do anything with the args

canton7•3/10/23, 7:21 PM

What do you mean by that? What would they do with the instance of EventArgs.Empty?

Thinker•3/10/23, 7:23 PM

I meant EventHsndler<T>

canton7•3/10/23, 7:23 PM

EventHandler<EventArgs> is the same as the non generic EventHandler