Core Data causing crash on iPhone 3

Question

I'm getting a strange error with core data. Sometimes, but not all the time my app will crash when I try to access a core data object.

It happens regularly on iPhone 3's and only sometimes on iPhone 4's. I looked at my device log and narrowed it down to an issue with core data. The line the logs refer to is below, tripInstructor is a core data object, its a property of the AppManager class. Not sure if this makes a big difference but I do declare the property as being "nonatomic, retain".

Thanks for any advice

[self.supervisorLbl setText:[AppManager sharedAppManager].tripInstructor.name];

Date/Time:       2011-06-12 20:55:24.865 +1000
OS Version:      iPhone OS 4.3.3 (8J2)
Report Version:  104


Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x00000000, 0x00000000
Crashed Thread:  0

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   libsystem_kernel.dylib          0x33e8da1c pthread_kill + 8
1   libsystem_c.dylib               0x35e5b3b4 pthread_kill + 52
2   libsystem_c.dylib               0x35e53bf8 abort + 72
3   libstdc++.6.dylib               0x33508a64 __gnu_cxx::__verbose_terminate_handler() + 376
4   libobjc.A.dylib                 0x33f1106c _objc_terminate + 104
5   libstdc++.6.dylib               0x33506e36 _cxxabiv1::_terminate(void (*)()) + 46
6   libstdc++.6.dylib               0x33506e8a std::terminate() + 10
7   libstdc++.6.dylib               0x33506efe __cxa_rethrow + 62
8   libobjc.A.dylib                 0x33f10fd8 objc_exception_rethrow + 4
9   CoreData                        0x35624f66 _PFFaultHandlerLookupRow + 1450
10  CoreData                        0x356799ba -[NSFaultHandler fulfillFault:withContext:] + 14
11  CoreData                        0x35678782 _PF_FulfillDeferredFault + 354
12  CoreData                        0x35623f18 _sharedIMPL_pvfk_core + 52
13  CoreData                        0x35626b68 _pvfk_5 + 4
14  eLogger                         0x0000e346 -[VicLogVC viewWillAppear:] (VicLogVC.m:207)
15  UIKit                           0x3636bf14 -[UINavigationController _startTransition:fromViewController:toViewController:] + 604
16  UIKit                           0x3636bc3c -[UINavigationController _startDeferredTransitionIfNeeded] + 176
17  UIKit                           0x3635dd56 -[UINavigationController pushViewController:transition:forceImmediate:] + 634
18  UIKit                           0x3635dacc -[UINavigationController pushViewController:animated:] + 28
19  eLogger                         0x00025332 -[TripScreenVC _populateAndDisplayVicLog] (TripScreenVC.m:221)
20  eLogger                         0x00025492 -[TripScreenVC _determineLogScreen] (TripScreenVC.m:258)
21  eLogger                         0x000255d4 -[TripScreenVC buttonPressed:] (TripScreenVC.m:307)
22  CoreFoundation                  0x30d4356a -[NSObject(NSObject) performSelector:withObject:withObject:] + 18
23  UIKit                           0x36343ec2 -[UIApplication sendAction:to:from:forEvent:] + 78
24  UIKit                           0x36343e62 -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 26
25  UIKit                           0x36343e34 -[UIControl sendAction:to:forEvent:] + 32
26  UIKit                           0x36343b86 -[UIControl(Internal) _sendActionsForEvents:withEvent:] + 350
27  UIKit                           0x3634441c -[UIControl touchesEnded:withEvent:] + 336
28  UIKit                           0x36342bee -[UIWindow _sendTouchesForEvent:] + 362
29  UIKit                           0x36342568 -[UIWindow sendEvent:] + 256
30  UIKit                           0x3632b30c -[UIApplication sendEvent:] + 292
31  UIKit                           0x3632ac4c _UIApplicationHandleEvent + 5084
32  GraphicsServices                0x34e2be70 PurpleEventCallback + 660
33  CoreFoundation                  0x30daaa90 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION + 20
34  CoreFoundation                  0x30dac838 __CFRunLoopDoSource1 + 160
35  CoreFoundation                  0x30dad606 __CFRunLoopRun + 514
36  CoreFoundation                  0x30d3debc CFRunLoopRunSpecific + 224
37  CoreFoundation                  0x30d3ddc4 CFRunLoopRunInMode + 52
38  GraphicsServices                0x34e2b418 GSEventRunModal + 108
39  GraphicsServices                0x34e2b4c4 GSEventRun + 56
40  UIKit                           0x36355d62 -[UIApplication _run] + 398
41  UIKit                           0x36353800 UIApplicationMain + 664
42  eLogger                         0x00002ff8 main (main.m:14)
43  eLogger                         0x00002fa0 start + 32

Answer 1

You are likely holding on to an invalid reference to a managed object, it looks like it was turned into a fault by the managed object context, perhaps after calling -save: or -reset on the context.

If you deleted an object from your store, and still held a reference to the managed object in the ivar then that could be the cause of this error. The object will be deleted by CoreData and turned into a fault when -save: is called (at which point you should nil and reset your ivars). But, when you try to fault the object (by accessing one or more of it's properties) it won't be found in the store because you deleted it.