I'm currently developping an application which uses CoreData and a NSFectchedResultsController. This application only contains one UITableView which uses a NSFetchedResultsController.
1/ When the application is launched, another thread is detached. In this new thread, a WS call permits to retrieve data from a web server. After the WS call, I store data in my CoreData DB with another NSManagedObjectContext (Apple's best practice: Another thread => Another context). I have to delete all objects of this entity before saving new objects. I merge this other context with the main context via mergeChangesFromContextDidSaveNotification.
// Data Manager (in another thread)
NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(contextDidSave:)
name:NSManagedObjectContextDidSaveNotification
object:context];
[context setMergePolicy:NSMergeByPropertyObjectTrumpMergePolicy];
[context setPersistentStoreCoordinator:[self getPersistentStoreCoordinator]];
...
for (NSManagedObject * obj in objects)
{
[context deleteObject:obj];
}
...
for(NSDictionary *serverObj in serverObjects)
{
objAd = [NSEntityDescription
insertNewObjectForEntityForName:@"MyEntity"
inManagedObjectContext:context];
...
}
[context save:&error];
[[NSNotificationCenter defaultCenter] removeObserver:self name:NSManagedObjectContextDidSaveNotification object:context];
[context release];
...
- (void)contextDidSave:(NSNotification *)notification
{
SEL selector = @selector(mergeChangesFromContextDidSaveNotification:);
[[self getContext] performSelectorOnMainThread:selector withObject:notification waitUntilDone:YES];
}
- (NSManagedObjectContext *) getContext
{
return [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
}
- (NSPersistentStoreCoordinator *) getPersistentStoreCoordinator
{
return [(AppDelegate *)[[UIApplication sharedApplication] delegate] persistentStoreCoordinator];
}
2/ Here is my NSFectchedResultsController's getter:
// UIView
- (NSFetchedResultsController*) offersFRC {
if (offersFRC == nil)
{
NSManagedObjectContext *l_ManagedObjectContext = [[DataManager sharedDataManager] getContext];
NSFetchRequest *l_FetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *l_Entity = [NSEntityDescription entityForName:@"MyEntity" inManagedObjectContext:l_ManagedObjectContext];
[l_FetchRequest setEntity:l_Entity];
[l_FetchRequest setFetchBatchSize:5];
NSNumber *sortType = [self.searchCriterions objectForKey:@"sortType"];
NSSortDescriptor *l_SortDescriptor = [[NSSortDescriptor alloc] initWithKey:[Constants getFieldNameBySortType:sortType] ascending:[Constants isAscendingBySortType:sortType]];
[l_FetchRequest setSortDescriptors:[NSArray arrayWithObjects:l_SortDescriptor, nil]];
[l_SortDescriptor release];
NSFetchedResultsController *l_FetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:l_FetchRequest managedObjectContext:l_ManagedObjectContext
sectionNameKeyPath:nil
cacheName:nil];
[l_FetchRequest release];
[self setOffersFRC:l_FetchedResultsController];
[l_FetchedResultsController release],l_FetchedResultsController = nil;
[self.offersFRC setDelegate:self];
}
return offersFRC;
}
3/ I've got the following error when the application is launched:
2012-02-29 11:56:09.119 Nanopost[1996:207] *** Terminating app due to uncaught exception 'NSObjectInaccessibleException', reason: 'CoreData could not fulfill a fault for '0x5c3c760 <x-coredata://E176B0A1-275B-4332-9231-49FD88238C2B/Ads/p231>''
*** Call stack at first throw:
(
0 CoreFoundation 0x02bfe919 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x02e595de objc_exception_throw + 47
2 CoreData 0x028b833f _PFFaultHandlerLookupRow + 1407
3 CoreData 0x028b5ee3 _PF_FulfillDeferredFault + 499
4 CoreData 0x028b9f3f _sharedIMPL_pvfk_core + 95
5 CoreData 0x0292a010 _PF_Handler_Public_GetProperty + 160
6 Foundation 0x02442c4f -[NSSortDescriptor compareObject:toObject:] + 128
7 CoreData 0x0297db5e +[NSFetchedResultsController(PrivateMethods) _insertIndexForObject:inArray:lowIdx:highIdx:sortDescriptors:] + 286
8 CoreData 0x0297e1b2 -[NSFetchedResultsController(PrivateMethods) _postprocessInsertedObjects:] + 402
9 CoreData 0x029841bc -[NSFetchedResultsController(PrivateMethods) _managedObjectContextDidChange:] + 1804
10 Foundation 0x02380c1d _nsnote_callback + 145
11 CoreFoundation 0x02bd6cf9 __CFXNotificationPost_old + 745
12 CoreFoundation 0x02b5611a _CFXNotificationPostNotification + 186
13 Foundation 0x023767c2 -[NSNotificationCenter postNotificationName:object:userInfo:] + 134
14 CoreData 0x028c0519 -[NSManagedObjectContext(_NSInternalNotificationHandling) _postObjectsDidChangeNotificationWithUserInfo:] + 89
15 CoreData 0x028f802b -[NSManagedObjectContext mergeChangesFromContextDidSaveNotification:] + 1579
16 Foundation 0x02395e9a __NSThreadPerformPerform + 251
17 CoreFoundation 0x02bdfd7f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
18 CoreFoundation 0x02b3e2cb __CFRunLoopDoSources0 + 571
19 CoreFoundation 0x02b3d7c6 __CFRunLoopRun + 470
20 CoreFoundation 0x02b3d280 CFRunLoopRunSpecific + 208
21 CoreFoundation 0x02b3d1a1 CFRunLoopRunInMode + 97
22 GraphicsServices 0x031e62c8 GSEventRunModal + 217
23 GraphicsServices 0x031e638d GSEventRun + 115
24 UIKit 0x0063cb58 UIApplicationMain + 1160
25 Nanopost 0x0000230a main + 170
26 Nanopost 0x00002255 start + 53
)
terminate called after throwing an instance of '_NSCoreDataException'
Important Notes:
- It crashes only on iOS4
- controllerWillChangeContent is the last function called in my code before application's crash. controllerDidChangeContent / didChangeObject/ didChangeSection are not called.
- When I comment [l_FetchRequest setFetchBatchSize:5] => No more crashes
- When I add a [context save:&error] after objects deletion and before new objects insertion => No more crashes
- When I use [l_FetchRequest setFetchBatchSize:24] => Crashes
- When I use [l_FetchRequest setFetchBatchSize:25] => No more crashes
I have spent a lot of time trying to understand this issue so Thank you very much in advance for your answers!
Thomas
Edit 1 (@Jody): Hi Jody and thank you very much for your answers!
Here is the code used for handling contextDidSave:
- (void)contextDidSave:(NSNotification *)notification
{
SEL selector = @selector(mergeChangesFromContextDidSaveNotification:);
[[self getContext] performSelectorOnMainThread:selector withObject:notification waitUntilDone:YES];
}
"you first have to tell me more about the context you are using":
I use 2 contexts in this application:
N° 1 : Created by default in the AppDelegate when you create XCodeProject. This context is used by my FRC and permits to display UITableView's rows.
N° 2 : Created in my "DataManager" (first code block in my post), a singleton which permits to refresh my DB (WS Call, deletion, re-insertion, save).
When context N° 2 is saved, contextDidSave is called to merge this context with the main context (context N° 1). After that, my FRC delegate's method "controllerWillChangeContent" is called. I don't think it will help to show the code contained in this method because even if I just put a NSLog, it crashes after this method (I put a lot of NSLog and the NSLog contained in controllerWillChangeContent is the last which is displayed before the crash).
I have posted on Apple Dev Forum and there is an interesting answer: https://devforums.apple.com/thread/152172?tstart=0
Edit 2 (@Jody): Hi Jody!
As you can see in the following method, my FRC doesn't use the MOC from the other thread:
- (NSManagedObjectContext *) getContext
{
return [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
}
This method of my "DataManager" returns AppDelegate's MOC (= main thread MOC)
