Crash in actionForLayer:forKey:

Question

I have a cryptic EXC_BAD_ACCESS when changing some UILabel's frame. The crash is random, usually I have to repeat the conditions for several minutes.

Enabling NSZombies, as well as other memory debug flags (NSDebugEnabled, MallocStackLogging), doesn't help, the crash stills stays as opaque : just a BAD_ACCESS with no message in the console. The target seems correct and alive, so it doesn't look like a deallocated memory problem.

To get some more info, I subclassed UILabel and rewrote the crashing function :

@implementation TestUILabel
- (id<CAAction>)actionForLayer:(CALayer *)layer forKey:(NSString *)event {
    return [super actionForLayer:layer forKey:event];
}
@end

It crashes in the super's method, but on inspection everything seems correct (printing retainCount for 'self' and 'layer' gives respectively 3 and 2) :

(gdb) po self

< TestUILabel: 0x6ac2800; baseClass = UILabel; frame = (173 174; 0 0); text = '54 m²'; opaque = NO; autoresize = LM+TM; autoresizesSubviews = NO; userInteractionEnabled = NO; animations = { position=< CABasicAnimation: 0xe07ba60>; }; layer = < CALayer: 0xbf1b950>>

(gdb) po event

bounds

(gdb) po layer

< CALayer:0xbf1b950; position = CGPoint (173 174); bounds = CGRect (0 0; 0 0); delegate = < TestUILabel: 0x6ac2800; baseClass = UILabel; frame = (173 174; 0 0); text = '54 m²'; opaque = NO; autoresize = LM+TM; autoresizesSubviews = NO; userInteractionEnabled = NO; animations = { position=< CABasicAnimation: 0xe07ba60>; }; layer = < CALayer: 0xbf1b950>>; contents = < CGImage 0xe04ed60>; opacity = 1; animations = [position=< CABasicAnimation: 0xe07ba60>]>

Did someone get a similar problem ? Or have any ideas where this could come from ?

Thanks in advance !

Edit: here's the complete crash backtrace :

Thread 1, Queue :
com.apple.main-thread
#0 0x00459b2c in -[UIView(CALayerDelegate) actionForLayer:forKey:] ()
#1 0x00eaaac7 in -[CALayer actionForKey:] ()
#2 0x00ea80fe in actionForKey(CALayer*, CA::Transaction*, NSString*) ()
#3 0x00ea8066 in beginChange(CALayer*, CA::Transaction*, unsigned int, objc_object*&) ()
#4 0x00eaba3a in CALayerSetPosition(CALayer*, CA::Vec2 const&, bool) ()
#5 0x00eab8b5 in -[CALayer setPosition:] ()
#6 0x00eab7cc in -[CALayer setFrame:] ()
#7 0x0045739d in -[UIView(Geometry) setFrame:] ()
#8 0x00542a68 in -[UILabel setFrame:] ()
#9 0x0000a97f in -[MosaicElementView setupWithAdvert:] at /Users/eino/Prog/AJ/Classes/Search/SubViews/MosaicElementView.m:30
#10 0x00079cb9 in -[SearchResultsViewController setupElement:withCell:indexPath:actualIndex:] ()
#11 0x000797a2 in -[SearchResultsViewController tableView:cellForRowAtIndexPath:] ()
#12 0x004957fa in -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:withIndexPath:] ()
#13 0x0048b77f in -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:] ()
#14 0x004a0450 in -[UITableView(_UITableViewPrivate) _updateVisibleCellsNow:] ()
#15 0x00498538 in -[UITableView layoutSubviews] ()
#16 0x00eb0451 in -[CALayer layoutSublayers] ()
#17 0x00eb017c in CALayerLayoutIfNeeded ()
#18 0x00ea937c in CA::Context::commit_transaction(CA::Transaction*) ()
#19 0x00ea90d0 in CA::Transaction::commit() ()
#20 0x00ed97d5 in CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) ()
#21 0x017e9fbb in __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ ()
#22 0x0177f0e7 in __CFRunLoopDoObservers ()
#23 0x01747bd7 in __CFRunLoopRun ()
#24 0x01747240 in CFRunLoopRunSpecific ()
#25 0x01747161 in CFRunLoopRunInMode ()
#26 0x01e7d268 in GSEventRunModal ()
#27 0x01e7d32d in GSEventRun ()
#28 0x0043042e in UIApplicationMain ()
#29 0x000021fe in main at /Users/eino/Prog/AJ/main.m:11

The crasing line from frame 9 is basically just the frame change :

labelPrice.frame = rect;

with rect being a correct CGRect (106, 143, 86, 22).

Mr Berna, no unfortunately, event is just a string containing @"bounds" — Eino Gourdin
Can you show the declaration of the rect variable? Don't you mean CGRectMake(106, 143, 86, 22); instead of CGRect(106, 143, 86, 22);? Also can you show the instantiation of your UILabel? Have you tried using the initWithFrame: constructor instead of setting the frame property? — fulvio
labelPrice is an IBOutlet to an object instantiated from a xib file. However its size has to change to accomodate new text, so this line has to be called. Even then, it works fine 99,5% of the time, as it should. As for the rect variable, it is indeed directly a CGRectMake in production code, however after tests I have already discarded the possibility of the problem being there : when the crash occurs, the used CGRect has always correct values (like 106, 143, 86, 22) ; so the failure comes from the setFrame: itself, not from the CGRect construction, that's why I left this part out. — Eino Gourdin

David Hodge David Hodge · Accepted Answer · 2011-09-08T06:51:43

You probably already checked for this, but it's worth shot...

Are you certain that you aren't doing anything that would effect any UI elements in a background thread? Perhaps you're doing some computation related to this search and it changes a property of some view.

I have seen his sort of thing in cases where I forgot a performSelectorOnMainThread:withObject:waitUntilDone: call and then altered the UI in the background.

Crash in actionForLayer:forKey:

2 Answers