bad access with array of sprites - cocos2d-iphone

Question

I am populating an NSMutableArray with CCSprites and adding them to the current layer which is added to a scene. When i try to access the elements of the array I get a bad access error
sprites = [[[NSMutableArray alloc] init]autorelease];
int j = 0;
for (int i=0; i<[sprites count]; i++)
{
j=i+1;
sprite = [CCSprite spriteWithFile:[NSString stringWithFormat:#"intro%d.png",j]];
sprite.position = ccp(WIDTH/2, HEIGHT/2+(i*HEIGHT));
[sprites addObject:sprite];
}
for (int i = 0; i<[sprites count]; i++)
{
[self addChild:[sprites objectAtIndex:i]];
}
[self scheduleUpdate];
}
return self;
This is done in the init method and sprites and sprite are declared in the header file. Inside the update method, I have
sprite = [sprites objectAtIndex:1];
sprite.position = ccpAdd(sprite.position, ccp(0,dy));
CCSprite* spr = [sprites objectAtIndex:2];
spr.position = ccpAdd(spr.position, ccp(0,dy));
When control is passed to the update method, I get a bad access. I would be glad if anyone could help me

Answer 1

This is happening because you created an autorelease object, that you then try to access later in your update code. The sprites array has a retain count of zero (since it is autorelease), and gets deallocated, you then try to access it, and get a bad-access error.
To fix, you should not make the sprites array an autorelease object. Since you plan on using the object later on in your code, you should keep it retained (by not adding the autorelease). You should also then make sure to release the array in the (whatever the parent object that is operating on the array)'s dealloc method.
- ( void ) dealloc {
[ sprites release ];
[ super dealloc ];
}

Answer 2

You should retain the sprites array (make certain you release it in your object's dealloc). Since it is autoreleasable, during the cycle from your init to your update method, it gets released.
Also (strange) , if your code is as shown, sprites.count is 0 when you start your first loop. You wont get much in there :).

Answer 3

The others are right (the autorelease call is the culprit - you should just remove it and then release the array in the dealloc method of the scene).
Also note that [[[NSMutableArray alloc] init]autorelease] has the same effect as [NSMutableArray array] (for your scenario, though, this is not what you need).