Question

I have this code in my .m file, which is a Cocos 2D CCLayer class. I initialize an array in the init method and then I try to use contents of this array in the nextFrame method. But when the nextFrame method gets called, the contents of the array seem empty. When I try to get the first item, I receive an error message saying:

Program received signal “EXC_BAD_ACCESS”

How can I successfully access the contents of this array in my nextFrame method?

NSMutableArray *cars;

-(id) init {
    cars = [NSMutableArray array];
    Car *car;
    car = [[Car alloc] init];
    [cars addObject:car];
    self.isTouchEnabled = YES;
}

- (void) nextFrame:(ccTime)dt {
    Car *car = [cars objectAtIndex:i]; // Program received signal "EXC_BAD_ACCESS" 
}

Car.h

#import <Foundation/Foundation.h>
#import "cocos2d.h";

@interface Car : NSObject {
    NSInteger type;
    CCSprite *sprite;
}

@property (readwrite, assign) NSInteger type;
@property (retain) CCSprite *sprite;

@end

Car.m

#import "Car.h"

@implementation Car

@synthesize type;
@synthesize sprite;

- (id)init
{
    self = [super init];
    if (self) {
        // Initialization code here.
    }

    return self;
}

- (void) dealloc {
    [sprite release];
    [super dealloc];
}

@end

Answer 1

You’re assigning the result of [NSMutableArray array] to an instance variable. That is an autoreleased object, which essentially means it doesn’t have any owners and thus will feel free to go away after the current runloop iteration*. You need to retain it if you want it to stick around (or just use [[NSMutableArray alloc] init], which returns an object you own).

_{* Basically. You should see the Cocoa memory mangement guide for more details. It’s pretty short but full of essential information.}