Question

尝试跟踪我在NSZombieEnabled时获得的错误。

当获取的结果控制器尝试执行提取时，我得到一个EXC_BAD_ACCESS。

调试器说：

-[CFNumber retain]: message sent to deallocated instance 0x6e88d10

Backtrace说：

#0  0x014bbe1e in ___forwarding___ ()
#1  0x014bbce2 in __forwarding_prep_0___ ()
#2  0x0145c490 in CFRetain ()
#3  0x0147929a in CFNumberCreate ()
#4  0x00b221ed in -[NSPlaceholderNumber initWithShort:] ()
#5  0x00b2216a in +[NSNumber numberWithShort:] ()
#6  0x010a549e in snapshot_get_value_as_object ()
#7  0x010a2a41 in _sharedIMPL_pvfk_core ()
#8  0x010a707d in -[NSManagedObject(_PFDynamicAccessorsAndPropertySupport)         _genericValueForKey:withIndex:flags:] ()
#9  0x010df6f0 in _PF_Handler_Public_GetProperty ()
#10 0x010df61d in -[NSManagedObject valueForKey:] ()
#11 0x00aea8d5 in -[NSObject(NSKeyValueCoding) valueForKeyPath:] ()
#12 0x00b1ad5e in _NSSortFunctionMany ()
#13 0x0152bf3f in __CFMergeSortArray_block_invoke_0 ()
#14 0x014b19d3 in __CFSimpleMergeSort ()
#15 0x014b1969 in __CFSimpleMergeSort ()
#16 0x014b1969 in __CFSimpleMergeSort ()
#17 0x014b1828 in CFSortIndexes ()
#18 0x014eb7e9 in CFMergeSortArray ()
#19 0x00b1828e in _sortedObjectsUsingDescriptors ()
#20 0x00b17fd9 in -[NSArray(NSKeyValueSorting) sortedArrayUsingDescriptors:] ()
#21 0x010853c6 in -[NSManagedObjectContext executeFetchRequest:error:] ()
#22 0x0118fc8f in -[NSFetchedResultsController performFetch:] ()
#23 0x000105c0 in -[RootViewController fetchedResultsController] (self=0x6d4bc80, _cmd=0x15a28) at /Users/david/Dropbox/Xcode/MyApp/MyApp/RootViewController.m:513
#24 0x0000e549 in -[RootViewController reloadTableView] (self=0x6d4bc80, _cmd=0x158d6) at /Users/david/Dropbox/Xcode/MyApp/MyApp/RootViewController.m:159
#25 0x01556ec9 in -[NSObject performSelector:withObject:withObject:] ()
#26 0x001dc5c2 in -[UIApplication sendAction:to:from:forEvent:] ()
#27 0x001dc55a in -[UIApplication sendAction:toTarget:fromSender:forEvent:] ()
#28 0x00281b76 in -[UIControl sendAction:to:forEvent:] ()
#29 0x0028203f in -[UIControl(Internal) _sendActionsForEvents:withEvent:] ()
#30 0x00281bab in -[UIControl sendActionsForControlEvents:] ()
#31 0x002cfa99 in -[UISegmentedControl _setSelectedSegmentIndex:notify:] ()
#32 0x002d1407 in -[UISegmentedControl touchesBegan:withEvent:] ()
#33 0x0020193f in -[UIWindow _sendTouchesForEvent:] ()
#34 0x00201c56 in -[UIWindow sendEvent:] ()
#35 0x001e8384 in -[UIApplication sendEvent:] ()
#36 0x001dbaa9 in _UIApplicationHandleEvent ()
#37 0x02442fa9 in PurpleEventCallback ()
#38 0x015291c5 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ ()
#39 0x0148e022 in __CFRunLoopDoSource1 ()
#40 0x0148c90a in __CFRunLoopRun ()
#41 0x0148bdb4 in CFRunLoopRunSpecific ()
#42 0x0148bccb in CFRunLoopRunInMode ()
#43 0x02441879 in GSEventRunModal ()
#44 0x0244193e in GSEventRun ()
#45 0x001d9a9b in UIApplicationMain ()
#46 0x000020ed in main (argc=1, argv=0xbffff5e8) at     /Users/david/Dropbox/Xcode/MyApp/MyApp/main.m:14

这是NSFetchedResultsController中的相关代码：

- (NSFetchedResultsController *)fetchedResultsController

{

    if (__fetchedResultsController != nil)
{
    return __fetchedResultsController;
}

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:kGestureEntity inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

[fetchRequest setFetchBatchSize:0];

// sort keys
NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:kCategory ascending:YES];
NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:kOrder ascending:YES]; // THIS IS AN INT 16 IN THE CORE DATA MODEL
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1, sortDescriptor2, nil];

[fetchRequest setSortDescriptors:sortDescriptors];

//filter for males or females by tab index
//set the tabIndex so the fetchedResultsController knows which sex to filter
NSUInteger tabIndex = self.appDelegate.tabBarController.selectedIndex;
NSString *theSex = [NSString string];
if (tabIndex == 0)
    theSex = vFemale;
else
    theSex = vMale;

//determine if sitting or standing
NSInteger segmentIndex = self.segmentedControl.selectedSegmentIndex;
NSString *sittingOrStanding = [NSString string];
if (segmentIndex == 0)
    sittingOrStanding = vSitting;
else
    sittingOrStanding = vStanding;

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K like %@ AND (%K like %@ OR %K like %@)", kSex, theSex, kSittingOrStanding, sittingOrStanding, kSittingOrStanding, vBothSittingAndStanding];
[fetchRequest setPredicate:predicate];

NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:kCategory cacheName:nil];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;

NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error]) //THIS IS WHERE EXC_BAD_ACCESS HAPPENS
    {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
}
[aFetchedResultsController release];
[fetchRequest release];
[sortDescriptor1 release];
[sortDescriptor2 release];
[sortDescriptors release];

return __fetchedResultsController;

}

我唯一可以想到的是我的核心数据模型中的kOrder属性被设置为Int 16.但是，我不确定是什么过早地释放了这个似乎通过保留的CFNumber私人方法。非常感谢任何帮助。

Edit1：头文件：

@property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;

然后在实施中：

@synthesize fetchedResultsController=__fetchedResultsController;

Edit2：为了清楚起见，我的应用程序在iOS 4上运行良好，只与iOS 5崩溃。

Answer 1

在调试器中设置NSZombieEnabled，MallocStackLogging和guard malloc。然后，当您的应用程序崩溃时，请在gdb控制台中输入：

(gdb) info malloc-history 0x6e88d10

将0x6e88d10替换为导致崩溃的"message sent to deallocated instance"对象的地址，您将获得更有用的堆栈跟踪，它可以帮助您查明代码中导致的确切行问题。

See this article for more detailed instructions.

Answer 2

你真的保留了fetchedResultsController吗？在你的标题中，你使用类似于@property（非原子，保留）的东西NSFetchedResultsController * fetchedResultsController; ？如果没有，那么你的FRC正在被解除分配，而CFNumber只是碰巧在响应者链末端被破坏的对象。

使用NSFetchedResultsController进行EXC_BAD_ACCESS

2 个答案: