cocos2d box2d sprite position crash - cocos2d-iphone

Question

I have the following code:
for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
{
if (b->GetUserData() != NULL)
{
CCSprite *itemSprite = (CCSprite*)b->GetUserData();
CGSize SpriteSize;
SpriteSize.height = itemSprite.contentSize.height;
SpriteSize.width = itemSprite.contentSize.width;
CGPoint SpritePosition=[itemSprite position];
}
}
Just get the position of sprite, but this program crash sometimes in:
SpriteSize.height = itemSprite.contentSize.height;
and this line:
CGPoint SpritePosition=[itemSprite position];
I am using cocos2d .99.5.
Edit: here is my crash log:
Exception Type: EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x0000000f
Crashed Thread: 0
Thread 0 Crashed:
0 libobjc.A.dylib 0x00002666 objc_msgSend_stret + 14
1 ShootTheMonkey 0x0004c066 -[LevelFour ccTouchBegan:withEvent:] (LevelFour.mm:1432)
2 ShootTheMonkey 0x00321bf0 -[CCTouchDispatcher touches:withEvent:withTouchType:] (CCTouchDispatcher.m:238)
3 ShootTheMonkey 0x00322454 -[CCTouchDispatcher touchesBegan:withEvent:] (CCTouchDispatcher.m:305)
4 ShootTheMonkey 0x003240ec -[EAGLView touchesBegan:withEvent:] (EAGLView.m:318)
5 UIKit 0x00053d72 -[UIWindow _sendTouchesForEvent:] + 254
6 UIKit 0x000536fe -[UIWindow sendEvent:] + 74
7 UIKit 0x0004f320 -[UIApplication sendEvent:] + 260
8 UIKit 0x0004ec8c _UIApplicationHandleEvent + 4772
9 GraphicsServices 0x00003b2c PurpleEventCallback + 660
10 CoreFoundation 0x00022d96 CFRunLoopRunSpecific + 2214
11 CoreFoundation 0x000224da CFRunLoopRunInMode + 42
12 GraphicsServices 0x000030d4 GSEventRunModal + 108
13 GraphicsServices 0x00003180 GSEventRun + 56
14 UIKit 0x0000342a -[UIApplication _run] + 374
15 UIKit 0x00001954 UIApplicationMain + 636
16 ShootTheMonkey 0x0000377e main (main.m:13)
17 ShootTheMonkey 0x0000373c start + 32

Answer 1

Since you do not post the crash dump or stack trace, I can only guess. AFAIK there are at least two reasons:
You assign objects of multiple classes to body->SetUserData(). The crash happens when you cast the user data to CCSprite when it's in fact not a CCSprite. Although I doubt this is the case since usually people assign objects of the same class to it.
The second reason is more likely to happen due to the way people usually depend on CCLayer to retain its CCSprite children (rather than explicitly retaining them). When you remove the CCSprites from the parent CCLayer, the latter releases the former and if retain count == 0 (very likely) the CCSprites are released from the heap. But remember that some of b2Bodies are still holding the pointers to these CCSprites through the user data attributes? So what happen when you iterate over all the bodies and try to use the released CCSprites that are still attached to the user data? Crash!
The way to fix this is that you need to remove the bodies when their corresponding sprites are removed from their CCLayer, by either subclassing CCSprite to add an ivar that points to b2Body, or by wrapping both objects (i.e sprite and body) in another class. Then add code to remove the body when the sprite is about to be de-alloc-ed.
Hope this helps. If not, please post more details (crash dump or stack trace).

Answer 2

Well, what we know for sure is the sprite was assigned to userData and it was later deallocated. I see that your assigned sprite was an autoreleased object and more likely it means that out of the scope sprite has received a release massage. To make sure that it is true, try to create sprite as follows: [[CCSprite alloc] initWithSprite:#"apple.png"]; But remember later you must release it.
If it worked for you, use the suggestion that above.