objective-c - 如果 managedobjectcontext 发生变化，那么必须删除、更新或添加某些内容，这总是正确的吗？

Question

NSUInteger numberOfChanges = moc.insertedObjects.count + moc.deletedObjects.count+moc.updatedObjects.count;

if (numberOfChanges ==0 )
{
    NSAssert([moc hasChanges]==false,@"[moc hasChanges]==false");
    return;
}

不知何故，断言失败了。我想知道为什么。所以什么都没有插入。什么都没有删除。什么都没有更新。然而 [moc hasChanges] 是真的吗？这种情况很少发生。然而，这根本不应该发生。

如果人们想看，这是完整的代码。

+(void)commit {

    [BGHPTools breakIfLock];
    NSManagedObjectContext *moc = [self managedObjectContext];

    NSArray * arUpdatedObjects = moc.updatedObjects.allObjects;

    NSArray * arUpdatedObjectsID = [arUpdatedObjects convertByPeformingSelector:@selector(objectID)];
    NSUInteger numberOfChanges = moc.insertedObjects.count + moc.deletedObjects.count+moc.updatedObjects.count;

    if (numberOfChanges ==0 )
    {
        //NSAssert([moc hasChanges]==false,@"[moc hasChanges]==false");
        return;
    }
    if (arUpdatedObjectsID.count) {
        while (false);
    }

    [BGFetchClass vAddObjectIDCachesForArray:moc.insertedObjects.allObjects];
    [BGFetchClass vDeleteObjectsForArray:moc.deletedObjects.allObjects];
    /*if (numberOfChanges ==0 )
    {
        NSAssert([moc hasChanges]==false,@"[moc hasChanges]==false");
        return;
    }*/
    //NSAssert([moc hasChanges],@"[moc hasChanges]==true");
    __block NSError *error;

    __block BOOL saveSuccesfully;

    [moc performBlockAndWait:^{
        @synchronized([BGFetchClass class])
        {
            saveSuccesfully = [moc save:&error];
            if (!saveSuccesfully) {
                CLog(@"Error in Saving %@", error);
            }
            else{
            }
        }
    }];

    if (![NSThread isMainThread]) {
        if (arUpdatedObjectsID.count) { //When we're adding new objects, this won't be called. That is the only time commit is called while we are synching
            [BGHPTools vDoForeGroundAndWait:^{
                NSManagedObjectContext * moc =[BGMDCRManagedObjectContextThreadHandler managedObjectContext];
                for (NSManagedObjectID * moi in arUpdatedObjectsID) {
                    NSManagedObject * mo = [moc existingObjectWithID:moi error:nil];
                    NSAssert(mo!=nil, @"Object can't possibly be nil");
                    [mo turnToFault];
                }
            }];
        }
    }

    NSManagedObjectContext * parentMoc = [self managedObjectContextMainContext]; //Main parent is not nsmainqueueconcurency type. Hence, this is save
    [parentMoc performBlockAndWait:^{
        if (![parentMoc save:&error])
        {
            CLog(@"Error in Saving %@", error);// handle error
        }
    }];
    NSAssert(error==nil, @"Error must be nill");
}

Answer 1

有一种记录在案的情况可以让您出现这种行为。
来自 NSManagedObjectContext文档:

NSManagedObjectContext deletedObjects

Discussion
The returned set does not necessarily include all the objects that have been deleted (using deleteObject:)—if an object has been inserted and deleted without an intervening save operation, it is not included in the set.

会不会是你的情况？