How should I manage events in XNA on the Windows Phone 7 without impacting performance?

Question

It's best-practice to not to create lots of short-lived temporary objects the heap as it'll eventually force a garbage collection during game-play.

It is best to create short lived value objects.

Where does this leave us with event handlers? My game object fires events quite frequently, so I don't want to create new MyThingDidSomethingEventArgs every time.

What's the alternative. What do you use?

Answer 1

See this document: How to: Publish Events that Conform to .NET Framework Guidelines (C# Programming Guide).

Ignore it.

There is no compelling reason to follow those guidelines when you are making a game. Make your own delegate type that takes appropriate types (either existing object references or value types):

public delegate void DidSomethingHandler(MyThing what, Vector2 where);
public event DidSomethingHandler DidSomething;

Or, if you want to be especially lazy (protip: you want to be especially lazy), you can even just do this:

public event Action<MyThing, Vector2> DidSomething;

(If creating your own delegate provides better documentation or will be used in many places, do that, otherwise just use an Action.)

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Footnote: When are those event guidelines applicable? When someone else will be consuming your code - especially in versioning situations. See also: What are the benefits of having events conforming to Net guidelines?.

Answer 2

You could let MyThingDidSomethingEventArgs be a struct, these are generally (not always) created on the stack instead of on the heap. However this is only viable if you include only value-types in the struct.

However more important is: what is 'quite frequently', if it's not dozens times per frame than its not going to be an issue so you shouldn't be worrying about this too soon. I understand you want to keep to best practices, but this isn't a best practice more of a optimization hint that should only be applied after you've measured that performance is impacted because of frequent garbage collection.