iPhone crash during layer animation after being in background - ios

Question

I'm having trouble fixing a pesky crash. I can't figure out how to accurately reproduce it,
but it only occurs after the app comes out of the background. I get this crash every 2+ days.
In applicationDidBecomeActive:, I restart a timer that fires every 0.4 seconds. It calls:
- (void)rotate {
[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:0.3];
self.transform = CGAffineTransformMakeRotation(DEGREES_TO_RADIANS(-[LocationModel instance].heading.magneticHeading));
[UIView commitAnimations];
}
Also in RotateView, is the drawRect, whose body is at line 41 as seen in the crash report.
- (void)drawRect:(CGRect)rect {
[img drawInRect:rect]; // line 41
}
img is a small UIImage loaded with imageNamed: and stored in an ivar.
Any advice? I have little experience with crash reports.
Thanks!
Crash report:
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x3001b482
Crashed Thread: 0
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0 libobjc.A.dylib 0x333a6c98 objc_msgSend + 16
1 MyApp 0x000259bc -[RotateView drawRect:] (RotateView.m:41)
2 UIKit 0x34f4a9fe -[UIView(CALayerDelegate) drawLayer:inContext:] + 258
3 QuartzCore 0x3058efa6 -[CALayer drawInContext:] + 86
4 QuartzCore 0x3058ed24 _ZL16backing_callbackP9CGContextPv + 32
5 QuartzCore 0x3058e776 CABackingStoreUpdate + 1226
6 QuartzCore 0x3058e178 -[CALayer _display] + 724
7 QuartzCore 0x3058de86 -[CALayer display] + 134
8 QuartzCore 0x30582706 CALayerDisplayIfNeeded + 178
9 QuartzCore 0x305821c6 CA::Context::commit_transaction(CA::Transaction*) + 214
10 QuartzCore 0x30581fd0 CA::Transaction::commit() + 184
11 QuartzCore 0x30580900 CA::Transaction::pop() + 120
12 QuartzCore 0x3058087e +[CATransaction commit] + 22
13 UIKit 0x35096bcc _UIWindowUpdateVisibleContextOrder + 136
14 UIKit 0x35096c60 +[UIWindow _prepareWindowsForAppResume] + 4
15 UIKit 0x3508f3de -[UIApplication _handleApplicationResumeEvent:] + 66
16 UIKit 0x34f39e20 -[UIApplication handleEvent:withNewEvent:] + 2724
17 UIKit 0x34f3920e -[UIApplication sendEvent:] + 38
18 UIKit 0x34f38c4c _UIApplicationHandleEvent + 5084
19 GraphicsServices 0x35873e70 PurpleEventCallback + 660
20 GraphicsServices 0x35873efa PurpleEventSignalCallback + 10
21 CoreFoundation 0x36126a72 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 6
22 CoreFoundation 0x36128758 __CFRunLoopDoSources0 + 376
23 CoreFoundation 0x361294e4 __CFRunLoopRun + 224
24 CoreFoundation 0x360b9ebc CFRunLoopRunSpecific + 224
25 CoreFoundation 0x360b9dc4 CFRunLoopRunInMode + 52
26 GraphicsServices 0x35873418 GSEventRunModal + 108
27 GraphicsServices 0x358734c4 GSEventRun + 56
28 UIKit 0x34f63d62 -[UIApplication _run] + 398
29 UIKit 0x34f61800 UIApplicationMain + 664
30 MyApp 0x000026c4 main (main.m:14)
31 MyApp 0x0000266c start + 32

Answer 1

EXC_BAD_ACCESS generally means you released an object then called that object later. Try enabling NSZombies to find it. There are numerous tutorials on how to do it. Here's one to start http://www.touch-code-magazine.com/how-to-debug-exc_bad_access/