CODEWITHSUNDEEP
iosobjective-ccocos2d-iphone
its me
its me

Reputation: 241

raywenderlich tutorial - simple iphone game - part2

I am using the second part of the iphone games tutorial, and I am confused about the ccTouchesEnded method's implementation. It is where the 'shooting' is implemented: the player (a cannon) is turned to the touched direction, and the projectile is shot. The part that's unclear to me is: _nextProjectile seems to be released while it could still be in use (by the code right below it - _nextProjectile runAction). Could you please explain why is it safe to release the object at this point?

- (void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

[_player runAction:

 [CCSequence actions:

  [CCRotateTo actionWithDuration:rotateDuration angle:cocosAngle],

  [CCCallBlock actionWithBlock:^{

     // OK to add now - rotation is finished!

     [self addChild:_nextProjectile];

     [_projectiles addObject:_nextProjectile];



     // Release

     [_nextProjectile release];

     _nextProjectile = nil;

 }],

  nil]];



// Move projectile to actual endpoint

[_nextProjectile runAction:

 [CCSequence actions:

  [CCMoveTo actionWithDuration:realMoveDuration position:realDest],

  [CCCallBlockN actionWithBlock:^(CCNode *node) {

     [_projectiles removeObject:node];

     [node removeFromParentAndCleanup:YES];

 }],

  nil]];



}

Upvotes: 2

Views: 164

Answers (1)

mmvie
mmvie

Reputation: 2581

Earlier on in ccTouchesEnded:withEvent: you increased the retain count of _nextProjectile on this line:

_nextProjectile = [[CCSprite spriteWithFile:@"projectile2.png"] retain];

So at some point later on you have to decrease the retain count to prevent a memory leak. In other words: you are responsable for releasing this retain. That is where this line is coming from:

[_nextProjectile release];

Why is it safe to release it at that point? The pieces of code you posted in your question are both actually actions in a sequence of actions.

[_player runAction:[CCSequence actions:...]];

Performing an action on an object increases the retain count on that object. This means the action object itself creates and holds another reference to _nextProjectile. The sequence of actions is created before the actions are actually performed, hence the action object already has its own reference to _nextProjectile. So releasing it in one of the actions is actually safe. They waited with releasing _nextProjectile until these lines passed:

[self addChild:_nextProjectile];
[_projectiles addObject:_nextProjectile];

A release before these lines would probably (I haven't looked at any other code than ccTouchesEnded:withEvent:) result in a EXC_BAD_ACCESS runtime error.

Here is some more info about the retain count: cocos2d forum

Upvotes: 1

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