Question

Although experienced with OOP, I am an absolute newbie with Objective-C. I have the following code:

// header files have been imported before this statement...
CCSprite *treeObstacle;
NSMutableArray *treeObstacles;

@implementation HelloWorldLayer {
}

-(id) init
{
    // create and initialize our seeker sprite, and add it to this layer
    treeObstacles = [NSMutableArray arrayWithObjects: nil];        
    for (int i=0; i<5; i++) {
        treeObstacle = [CCSprite spriteWithFile: @"Icon.png"];
        treeObstacle.position = ccp( 450-i*20, 100+i*20 );
        [self addChild:treeObstacle];
        [treeObstacles addObject: treeObstacle];
    }
    NSLog (@"Number of elements in array = %i", [treeObstacles count]);
    return self;
}

- (void) mymethod:(int)i {
    NSLog (@"Number of elements in array = %i", [treeObstacles count]);
}

@end

The first NSLog() statement returns “Number of elements in array = 5”. The problem is that (although treeObstacles is a file-scope variable) when calling the method “mymethod”, I’ll get an EXC_BAD_ACCESS exception.

Can anybody please help me?

Thanks a lot
Christian

Answer 1

you created treeObstacles by

treeObstacles = [NSMutableArray arrayWithObjects: nil];

which will return an autoreleased object, and you didn’t retain it so it will be released soon

you have to retain it by calling retain on it

[treeObstacles retain];

of simple create it by

treeObstacles = [[NSMutableArray alloc] init];

and you need to remember to release it when done like

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

you need to read more about management in Objective-C
https://developer.apple.com/library/mac/#documentation/General/Conceptual/DevPedia-CocoaCore/MemoryManagement.html

or use ARC so no need to worry retain/release anymore
http://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html

---

another problem, you need to call [super init] in your init method

- (id)init {
    self = [super init];
    if (self) {
        // your initialize code
    }
}

otherwise your object won’t initialize properly