Cocos2d NSMutable Array mutated while enumerated - iphone

Question

I've been working on a game, and at a point I didn't have issues removing the enemy game objects (right now they are subclassed from CCSprite and I know that's not the best way)
But I'm not sure what I changed to make it crash when the program attempts to removeChild from _targets after they have been added to targetsToDelete.
I tried moving things around, I just don't know how I am adding or editing the array while its being created... Any help or advice would be great!
And actually if you had any pointers on how best to create game enemies, do you subclass NSObject or CCNode? I heard to divide them into component classes but I had no clue what they meant.
//Projectile Target collision
-(void)update:(ccTime)dt {
for (spygot *target in _targets) {
CGRect targetRect = CGRectMake(
target.position.x - (target.contentSize.width/2),
target.position.y - (target.contentSize.height/2),
target.contentSize.width,
target.contentSize.height);
//Collision Detection Player
CGRect playerRect2 = CGRectMake(
_controlledSprite.position.x - (_controlledSprite.contentSize.width/2),
_controlledSprite.position.y - (_controlledSprite.contentSize.height/2),
_controlledSprite.contentSize.width,
_controlledSprite.contentSize.height);
NSMutableArray *projectilesToDelete = [[NSMutableArray alloc] init];
for (Projectile *projectile in _projectiles)
{
NSMutableArray *targetsToDelete = [[NSMutableArray alloc] init];
CGRect projectileRect = CGRectMake(
projectile.position.x - (projectile.contentSize.width/2),
projectile.position.y - (projectile.contentSize.height/2),
projectile.contentSize.width,
projectile.contentSize.height);
BOOL monsterHit = FALSE;
if (CGRectIntersectsRect(projectileRect, targetRect))
{
NSLog(#"hit");
target.mhp = target.mhp - 1;
monsterHit = TRUE;
if (target.mhp <= 0)
{
[targetsToDelete addObject:target];
}
}
for (spygot *target in targetsToDelete)
{
[self removeChild:target cleanup:YES];
[_targets removeObject:target];
}
if (monsterHit)
{
[projectilesToDelete addObject:projectile];
}
[targetsToDelete release];
}
for (Projectile *projectile in projectilesToDelete)
{
[_projectiles removeObject:projectile];
[self removeChild:projectile cleanup:YES];
}
[projectilesToDelete release];
}

Answer 1

It looks like the code that you've pasted is all from within a for loop iterating over _targets. How does the variable target get initialized?

Answer 2

Usually when I get this sort of error it's because I have the code in a block or am in some other way on a nebulous thread. How sure are you that this bit of code is not running more than once at the same time?
You could try wrapping it in the following:
dispatch_async(dispatch_get_main_queue(), ^{
// do everything here.
});
As for advice about using CCSprite for your game enemy objects, my advice is fix it when it becomes a problem. Are you seeing issues with it right now? Premature optimization is almost as bad as doing it wrong in the first place. You'll know better at the end of the project how you should have done it earlier. ;)

Answer 3

I guess you know that you cannot remove elements from the array while you iterate over it. That is why you have targetsToDelete array.
But it looks to me that you do remove targets to soon.
Try this:
finish iterating the main loop and finish collecting targets to the targetsToDelete array and only after main loop is done remove the targets.