Objective-C game development: communication between components - objective-c

Question

I am using Cocos2d game development framework for iPhone.
Let's focus on the battle scene:
The battle scene has as children: battlers layer, HUD layer, menu layer, background layer, etc...
Sometimes, it is necessary that my battlers layer "contacts" my HUD layer (like call a function within it).
I find this hard. Basically, my battlers layer needs some kind of.. instance or reference of the HUD layer in order to call a function within it, right? But I don't know how to have such thing.
Currently, this is what I do:
The battlers layer will run a function in the scene (its parent), and, inside such function, I will "locate" the HUD layer child, and call the function I need in it.
Now, that is kind of inconvenient. What would you do in such situation?

Answer 1

It sounds to me that you may have over-designed this. What I might do is something like this.
I'd have an IScene. Each of my scene classes implements this IScene. IScene has a property called "HUD", another called "Menu", etc.
The current IScene is set into a global static instance ::CurrentScene
When the current scene needs to contact the menu, I say: ::CurrentScene->Menu->SomeFuncion().
Would that work for you?

Answer 2

I'd suggest you take a look at Cocoa's NSNotificationCenter and related classes. Apple has a guide to the subject here.
It might work something like this.
In your HUD layer, you subscribe to notifications with the name #"battleLayerStuff":
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(doThisWhenSomethingHappens:)
name:#"battleLayerStuff"
object:nil];
And in your battle layer, when something happens, you post a notification with the same name:
[[NSNotificationCenter defaultCenter] postNotificationName:#"battleLayerStuff"
object:battleObject];
The object part is optional, but can be helpful if you want to send more information than just "something happened".
If you want to extract information from the object you send you do this in the doThisWhenSomethingHappens: method:
- (void)doThisWhenSomethingHappens:(NSNotification *)notification
{
BattleObject *battleObject = (BattleObject *) notification.object;
// Do stuff with object
}

Answer 3

You could use NSNotification Center. This allows you to send messages in one object and have multiple other objects react to them.
// The object that wants to receive the message registers with NSNotificationcenter
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(receiveScoreUpdateEvent:)
name:#"scoreUpdateEvent"
object:nil ];
In the same object you need to define the method that your selector points to:
- (void)startLocating:(NSNotification *)notification {
NSNumber *scoreObject = [[notification userInfo] objectForKey:#"score"];
// Do something with the new score
}
Another object can then send a message with the updated score at any time and your HUD would react to it:
[[NSNotificationCenter defaultCenter] postNotificationName:#"scoreUpdateEvent"
object:self userInfo:[NSNumber numberWithInt:5345] forKey:#"score"]];