Sparrow Forum

1. 

   alex_h
   Moderator

   Hi there,

   I'm new to Objective C as a whole, so I'm struggling to make sure I implement memory management correctly within my sparrow framework game.
   I've created 3 screens (that extend sprite) - a start screen, game screen and game over screen. I've copied the screen management system used in the sparrow demo whereby there is a single "current screen" variable retained in the game implementation.
   The problem I have is that when I call removeFromParent on that and set it to nil, dealloc is never executed on any of my screens. This means it quickly runs out of memory if I run it on a real device. I am instantiating my screens in the same way that this is done in the demo:
   - SPSPrite * scene = [[GameScreen alloc] init];
   - [scene addEventListener:@selector(onComplete:) atObject:self forType: EVENT_COMPLETE];
   - currentScene = scene;
   - [self addChild:scene atIndex:0];
   - [scene release];

   Am I missing something obvious? If I try to call release on the currentScreen variable when I change screen, rather than removeFromParent and setting it to nil, everything breaks.

   cheers,

   Alex

   Posted 2 years ago #
2. 

   Daniel
   Primary Feather

   Hi Alex!

   Yeah, memory management is always the toughest topic for beginners in Objective C (once you've got used to the "unorthodox" syntax *g*). The funny thing is: at one moment, it just makes "click" in your head and you find out that it's not as difficult as it seemed at first.

   What you described in your post looks perfectly fine, so I cannot give you a definitive answer -- but I can help you narrow it down.

   There is one very handy property of all objects in objective C: retainCount. This is the variable that is affected by your retain/release-calls. Once it reaches zero, the object's dealloc-method will be called, and its memory will be released. Whenever I encounter a memory leak, I scatter NSLog-calls that print out the retain count. Like here:

   SPSprite *testSprite = [[SPSprite alloc] init];
   NSLog(@"retainCount: %d", testSprite.retainCount); // -> 1
   [self addChild:testSprite];
   NSLog(@"retainCount: %d", testSprite.retainCount); // -> 2
   [testSprite release];
   NSLog(@"retainCount: %d", testSprite.retainCount); // -> 1
   [testSprite removeFromParent];
   // cannot query retainCount now, object already released -
   // that means it would be 0.

   You can do that as well. Add those calls in your scene-class, too (just print out self.retainCount instead). This should help you find the exact line where the retain count is raised.

   The best advice I can give you concerning memory management is the following: Whenever you see a call to alloc or copy or retain -- then, and only then (!), you will need to call release somewhere. (I guess XCode should paint those keywords red ;).) You can see that in the sample above: event though the retain count is raised in addChild as well, that does not have to bother you -- you call release just because you called alloc before. The removeFromParent call does not matter -- once self (which might be a sprite) would have been destroyed, it would have released all its child automatically (SPSprite's dealloc method does that automatically).

   I hope that helps you a little bit!

   Best regards,
   Daniel

   Posted 2 years ago #
3. 

   alex_h
   Moderator

   Thanks Daniel,

   yes I also came across some information online about the retainCount variable. When I output this from my code I found that at the point I set my screen instance to nil, it still has a retainCount of 3! So obviously that is why dealloc is not being called. I'll have to try to find where my retainCount is being bumped up so high, I'll try printing out the retainCount line by line as you suggested.

   Thanks for the help!

   cheers,

   Alex

   Posted 2 years ago #
4. 

   Jule
   Member

   Hi,
   I'm working with sparrow some time now, and now I ran into a Memory Warning Level=1 and Memory Warning Level=2 and after these warnings my app crashes. I try and release everything I alloc.
   Also I keep some SPSprites for different scenes because I have Back buttons, but before every other draw I dealloc them and I draw them all over again.
   If I do dealloc on SPSprite everything in it releases right?
   I don't know what else to do...
   Thanks,
   Jule.

   Posted 1 year ago #
5. 

   Daniel
   Primary Feather

   Hi Jule!

   You could try to add break points in the dealloc-methods to see if they really get called. If not, you'll have to analyze who is retaining those objects, e.g. with the "retainCount" method I described above.

   For starters, it's also a good method to use the "Allocations" and "Leaks" performance tools ("Run - Run with performance tool") to find out what happens. Those tools are at first a little hard to understand, but it pays of playing around with them.

   The alloc-retain-(auto)release cycle is the thing in objective c that is always hardest to get used to -- but once you understand it fully, it suddenly makes sense. So the last tip is to re-read any documentation on memory management in objective c.

   Daniel

   Posted 1 year ago #

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