[英]Exception / Crash When Merging CoreData Managed Contexts
嘗試將托管上下文(在后台線程上運行)與我的主托管上下文(在mainthread上)合並時,我得到以下異常。 我似乎無法在我自己的@try表達式中捕獲異常。 有沒有人對此問題有任何見解?
我正在使用默認的合並策略,但我不確定這是否正確 - 這個問題是非常間歇性的 - 很少發生,但導致我的應用程序崩潰。
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x00000000, 0x00000000
Crashed Thread: 0
Last Exception Backtrace:
0 CoreFoundation 0x37e3b8bf __exceptionPreprocess + 163
1 libobjc.A.dylib 0x319211e5 objc_exception_throw + 33
2 CoreData 0x344b7ea5 -[NSSQLiteStatement cachedSQLiteStatement] + 1
3 CoreData 0x344b774f -[NSSQLiteConnection prepareSQLStatement:] + 55
4 CoreData 0x3455b049 -[NSSQLChannel selectRowsWithCachedStatement:] + 61
5 CoreData 0x34586d63 newFetchedRowsForFetchPlan_MT + 783
6 CoreData 0x344bfb07 -[NSSQLCore newRowsForFetchPlan:] + 351
7 CoreData 0x34565011 -[NSSQLCore fetchRowForObjectID:] + 1005
8 CoreData 0x344d1a57 -[NSSQLCore newValuesForObjectWithID:withContext:error:] + 195
9 CoreData 0x344d0f83 _PFFaultHandlerLookupRow + 423
10 CoreData 0x3450e111 -[NSFaultHandler fulfillFault:withContext:] + 25
11 CoreData 0x34518999 -[NSManagedObject(_NSInternalMethods) _newPropertiesForRetainedTypes:andCopiedTypes:preserveFaults:] + 77
12 CoreData 0x345178ef -[NSManagedObject(_NSInternalMethods) _newAllPropertiesWithRelationshipFaultsIntact__] + 79
13 CoreData 0x345284db -[NSManagedObjectContext(_NSInternalChangeProcessing) _establishEventSnapshotsForObject:] + 47
14 CoreData 0x3452694b -[NSManagedObjectContext deleteObject:] + 155
15 CoreData 0x345238a1 -[NSManagedObjectContext _mergeChangesFromDidSaveDictionary:usingObjectIDs:] + 813
16 CoreData 0x34522c35 -[NSManagedObjectContext mergeChangesFromContextDidSaveNotification:] + 189
17 myapp 0x0008f0e9 0x8d000 + 8425
18 CoreFoundation 0x37d9a22b -[NSObject performSelector:withObject:] + 43
19 Foundation 0x31d75757 __NSThreadPerformPerform + 351
20 CoreFoundation 0x37e0fb03 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
21 CoreFoundation 0x37e0f2cf __CFRunLoopDoSources0 + 215
22 CoreFoundation 0x37e0e075 __CFRunLoopRun + 653
23 CoreFoundation 0x37d914dd CFRunLoopRunSpecific + 301
24 CoreFoundation 0x37d913a5 CFRunLoopRunInMode + 105
25 GraphicsServices 0x3790ffcd GSEventRunModal + 157
26 UIKit 0x35221743 UIApplicationMain + 1091
我在nsoperation的start()中初始化背景上下文,如下所示:
AppDelegate *appController = [[UIApplication sharedApplication] delegate];
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[appController setPersistentStore:_managedObjectContext];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receivedDeletedObjects:) name:NSManagedObjectContextDidSaveNotification object:_managedObjectContext];
我還設置了一個通知事件,當在后台托管上下文中刪除對象時調用該事件,然后回調執行:
-(void)receivedDeletedObjects:(NSNotification *)note
{
AppDelegate *appController = [[UIApplication sharedApplication] delegate];
NSManagedObjectContext *mainContext = [self managedObjectContext];
[mainContext performSelectorOnMainThread:@selector(mergeChangesFromContextDidSaveNotification:) withObject:note waitUntilDone:NO];
}
這幾乎就是代碼。 我有4個不同的后台線程,每個后台線程都有自己的托管上下文,以這種方式與主上下文合並。 我想知道多個線程同時進入mergeChangesFromContextDidSaveNotification,但這不應該是這樣,因為它總是在mainthread上調用。
這個怎么樣:
(所有在AppDelegate中,從后台線程調用freshContextForBackgroundTask並使用save:來觸發合並。)注意syncObj是在使用許多后台線程時在應用委托中進行同步所需的普通NSObject實例(或者只是運氣不好)
-(NSManagedObjectContext*) freshContextForBackgroundTask {
@synchronized(syncObj) {
NSManagedObjectContext* r = [[NSManagedObjectContext alloc] init];
[r setPersistentStoreCoordinator:self.managedObjectContext.persistentStoreCoordinator];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(backgroundContextDidSave:)
name:NSManagedObjectContextDidSaveNotification
object:r];
return r;
}
}
- (void)backgroundContextDidSave:(NSNotification *)notification {
/* Make sure we're on the main thread when updating the main context */
//NSLog(@"merging change: %@",notification);
dispatch_async(dispatch_get_main_queue(), ^{
NSManagedObjectContext *context = [self managedObjectContext];
// this for loop may not be needed for your purpose.
for(NSManagedObject *object in [[notification userInfo] objectForKey:NSUpdatedObjectsKey]) {
[[context objectWithID:[object objectID]] willAccessValueForKey:nil];
}
[self.managedObjectContext mergeChangesFromContextDidSaveNotification:notification];
});
}
你的方法似乎很奇怪。 特別是當你將app delegate的持久存儲設置為新的初始化上下文中的(nil)時。
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