ObjC: Can't access ivar of custom class from outside

Question

I'm attempting to make a basic game in cocos2d, and I've gotten to the point where I'm attempting to scroll the background depending on the hero sprite's position. The hero's created alongside the controls in a class called GameplayLayer, and all works fine for non-scrolling backgrounds.

The book I'm following has given me some sample code to get the scrolling working based on when my character passes the half-way point, which seems perfect, but it's not executing, I believe this is because it's creating another instance of my Hero class, and there's no link between that instance, and the one that's displayed onscreen.

I'm assuming that I can fix this by making the working instance of my hero accessible from within the background scrolling class (which is called YrrasCoastBackgroundLayer), but I'm having a brain-block and can't get it to see it. I've tried a @property, but Xcode just won't see it in the other class.

Here's the .h file from the GameplayLayer class, where the hero is created / hooked up to controls, etc.:

#import "CCLayer.h"
#import "cocos2d.h"
#import "CommonProtocols.h"
#import "SneakyJoystick.h"
#import "SneakyButton.h"
#import "SneakyJoystickSkinnedBase.h"
#import "SneakyButtonSkinnedBase.h"
#import "HeroMale.h"
#import "GameCharacter.h"

@interface GameplayLayer : CCLayer <GameplayLayerDelegate> {
    CCSprite *playerSprite;
    SneakyJoystick *playerJoystick;
    SneakyButton *jumpButton;  
    CCSpriteBatchNode *sceneSpriteBatchNode;
    HeroMale *heroMale;
}

@property (nonatomic, readonly) SneakyJoystick *playerJoystick;
@property (nonatomic, readonly) SneakyButton *jumpButton;
@property (nonatomic, assign) HeroMale *heroMale;

@end

The YrrasCoastBackgroundLayer.h file definitely imports GameplayLayer.h, and here's the contents of the method in YrrasCoastBackgroundLayer.m file which I want to be able to access that *heroMale ivar:

- (void) adjustLayer {
    float heroXPosition = heroMale.position.x;
    CGSize screenSize = [[CCDirector sharedDirector] winSize];
    float halfOfTheScreen = screenSize.width / 2.0f;
    CGSize levelSize = [[GameManager sharedGameManager] getDimensionsOfCurrentScene];

    if ((heroXPosition > halfOfTheScreen) && (heroXPosition < (levelSize.width - halfOfTheScreen))) {
        float newXPosition = halfOfTheScreen - heroXPosition;
        [self setPosition:ccp(newXPosition, self.position.y)];
    }
}

I'm getting an Xcode error on the float heroXPosition = heroMale.position.x line, stating that heroMale is an undeclared identifier. How can I make it usable here, and will that even solve the problem?

UPDATE:

Here's the .h file for YrrasCoastBackgroundLayer:

#import "CCLayer.h"
#import "cocos2d.h"
#import "HeroMale.h"
#import "GameplayLayer.h"

@interface YrrasCoastBackgroundLayer : CCLayer {
    // Web Tutorial
    CCParallaxNode *backgroundNode;
    CCSprite *backgroundImage;

    // Book Tutorial
    CCSpriteBatchNode *sceneSpriteBatchNode;
    CCParallaxNode *parallaxNode;
}

@property (nonatomic, assign) GameplayLayer *gameplayLayer;

@end

And here's the YrrasCoastBackgroundLayer.m:

#import "YrrasCoastBackgroundLayer.h"

@implementation YrrasCoastBackgroundLayer

@synthesize gameplayLayer;

- (id) init {
    self = [super init];

if (self != nil) {

    // Web Tutorial
    backgroundNode = [CCParallaxNode node];
    [self addChild:backgroundNode z: -1];

    backgroundImage = [CCSprite spriteWithFile:@"yrras-coast-ipad-hd.png"];

    CGPoint dustSpeed = ccp(0.1, 0.1);

    [backgroundNode addChild:backgroundImage z:0 parallaxRatio:dustSpeed positionOffset:ccp(1024, [[CCDirector sharedDirector]winSize].height / 2)];

    self.gameplayLayer = gameplayLayer;

    [self scheduleUpdate];

    }
    return self;
}

- (void)update:(ccTime)deltaTime {

    // Web Tutorial
    // CGPoint backgroundScrollVel = ccp(-1000, 0);
    // backgroundNode.position = ccpAdd(backgroundNode.position, ccpMult(backgroundScrollVel, deltaTime));

    CCArray *listOfGameObjects = [sceneSpriteBatchNode children];
    for (GameCharacter *tempChar in listOfGameObjects) {
        [tempChar updateStateWithDeltaTime:deltaTime andListOfGameObjects:listOfGameObjects];
    }
    [self adjustLayer];

}

// Book Tutorial
- (void) adjustLayer {
    float heroXPosition = gameplayLayer.heroMale.position.x;
    CCLOG(@"heroXPosition is %f", gameplayLayer.heroMale.position.x);
    CGSize screenSize = [[CCDirector sharedDirector] winSize];
    float halfOfTheScreen = screenSize.width / 2.0f;
    CGSize levelSize = [[GameManager sharedGameManager] getDimensionsOfCurrentScene];
    if ((heroXPosition > halfOfTheScreen) && (heroXPosition < (levelSize.width - halfOfTheScreen))) {
        float newXPosition = halfOfTheScreen - heroXPosition;
        [self setPosition:ccp(newXPosition, self.position.y)];
    }
}

@end

Answer 1

You need an instance of your GameplayLayer to be passed to the YrrasCoastBackgroundLayer layer.

You can declare an assignable property in YrrasCoastBackgroundLayer :

@property (nonatomic, assign) GameplayLayer gamplayLayer;

and when you initialize your YrrasCoastBackgroundLayer pass the instance of the game play layer and in your adjustLayer method do :

float heroXPosition = gameplayLayer.heroMale.position.x;

EDIT :

assuming this is how you create your scene :

  MyScene *scene = [MyScene scene];
  gameplayLayer = [[GameplayLayer alloc] init];
  bgLayer = [[YrrasCoastBackgroundLayer alloc] init];
  bgLayer.gameplayLayer = gameplayLayer; // This is where you assign the gameplay Layer to the background layer;

  [scene addChild:bgLayer];
  [scene addChild:gameplayLayer];

  // Release both layers if you dont need them anymore here (scene addChild retains them when they are added)      
  [gameplayLayer release];
  [bgLayer release];

Answer 2

I am not sure how can you access heroMale as it is not member of YrrasCoastBackgroundLayer but of GameplayLayer. You would have to have object/instance of class GameplayLayer in order for you to access heroMale. That is the reason why you are getting undeclared identifier (heroMale is not property of class YrrasCoastBackgroundLayer).

Kind regards,
Bo