How to access instance from another class - ios

Question

Thanks for your help in advance!
I'm new to OOP, so this problem may be really basic, but I've searched for hours and still cannot find a good solution.
I'm using Cocos2d and Box2d in the project. In my GameLayer.mm file, I have a label to show current score. And there's is a custom sprite derived from CCSprite.
Now, I wanna increment current score from my custom sprite class when the property of sprite "isDead" is changed to true. As follows:
- (void) setIsDead
{
isDead = 1;
// then increment score
}
My question is how I can increment score from this subclass? I cannot access the instance or instance method of GameLayer.mm from this subclass. I tried to change the function of incrementing score from instance method to class method, and make score as a global instance, but I got duplicate error later.
Thanks for any advice!

Answer 1

Here is another approach I like: delegates.
First, go to your custom CCSprite header and create a new protocol. Basically, add this:
#protocol MyCustomDelegate
-(void)spriteGotKilled:(CCSprite*)sprite;
#end
Next, you need to modify your custom CCSprite to store its delegate. Your interface would look like this:
#interface MySprite {
id delegate;
}
#property (retain,nonatomic) id delegate;
Now go to GameLayer.h and make it implement the protocol:
#interface GameLayer : CCLayer <MyCustomDelegate>
Next implement the protocol method in your layer:
-(void)spriteGotKilled:(CCSprite*)sprite {
NSLog(#"%# got killed!",sprite);
}
And, finally, go to your setIsDead method:
-(void)setIsDead {
isDead = 1;
// Check if we have a delegate set:
if ([self delegate] != nil) {
// Check if our delegate responds to the method we want to call:
if ([[self delegate]respondsToSelector:#selector(spriteGotKilled:)]) {
// Call the method:
[[self delegate]spriteGotKilled:self];
}
}
}
When you create your sprite, you must set the layer as its delegate. Something like this:
MySprite *sprite = [[MySprite alloc]init];
[sprite setDelegate:self];
Now whenever your sprite dies, spriteGotKilled will be called in your layer.

Answer 2

You could use The Observer Design Pattern here in which an observer listens to an event and performs an action accordingly.
So in your GameLayer.mm add the observer in the init function:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(receiveIsDeadNotification:)
name:#"SpriteIsDeadNotification"
object:nil];
and add a function:
- (void) receiveIsDeadNotification:(NSNotification *) notification
{
if ([[notification name] isEqualToString:#"SpriteIsDeadNotification"])
//update your label here
}
and in your custom sprite ,add the following line in the setIsDead method
-(void) setIsDead{
isDead =1;
[[NSNotificationCenter defaultCenter]
postNotificationName:#"SpriteIsDeadNotification"
object:self];
}
also remember to remove the observer in the dealloc of GameLayer.mm
[[NSNotificationCenter defaultCenter] removeObserver:self];
This pattern will reduce coupling in your code as instances of one class are not trying to access the methods of another.