Core-Data不会保存在异步调用中

Question

我正在尝试使用核心数据来保存Google Firebase调用的数据。当我保存托管上下文时，它会保存，但当我退出应用程序并重新打开它时，所有数据都会消失。

ref.child(exhibit).observeSingleEvent(of: .value, with: { snapshot in
    for item in snapshot.children {
        let animalObject = animal(snapshot: item as! FIRDataSnapshot)
        let managedContext = self.appDelegate!.persistentContainer.viewContext
        let animalEntity = NSEntityDescription.insertNewObject(forEntityName: "Animal", into: managedContext)
        animalEntity.setValue(animalObject.name, forKeyPath: "name")
        animalEntity.setValue(animalObject.information!, forKeyPath: "information")
        animalEntity.setValue(animalObject.imageReference!, forKeyPath: "imageURL")
        self.animals!.append(animalObject)

        do {
            try managedContext.save()
        } catch let error as NSError {
            print("Couldn not save. \(error), \(error.userInfo)")
        }
    }
})

我知道快照正确地获取了数据。此外，我还尝试了参数名为forKey而不是forKeyPath的setValue。

Answer 1

关键在于“异步”这个词。您使用的是来自appDelegate的managedObjectContext，它可能在一个辅助线程的主队列上运行。您有几个选项：

• 从快照收集数据，然后在主线程上调用一个保存到appDelegate的managedObjectContext的方法。通过向notifications.
• create发送类型为privateQueueConcurrencyType (init(concurrencyType:) )的新managedObjectContext并将快照数据保存在一个块(performBlockAndWait())中，可以实现同样的目的。有关详细信息，请访问NSManagedObjectContext reference

Objective-C示例，假设已经设置了self.persistentContainer，并且数据在字典的NSArray中可用：`

- (void)saveData
{
    NSManagedObjectContext *_privateContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    _privateContext.persistentStoreCoordinator = _persistentContainer.persistentStoreCoordinator;

    __block __typeof__(self) blockSelf = self;
    [_privateContext performBlock:^(void) {
        NSError *error = nil;

        for (NSDictionary *animalDict in blockSelf.dataArray) {
            Animal *anAnimal = [Books managedObjectWithEntity:@"Animal" managedObjectContext:_privateContext];
            anAnimal.name = [animalDict valueForKey:@"name"];
            anAnimal.fluffiness = [animalDict valueForKey:@"fluffiness"];
        }

        if ([_privateContext save:&error]) {
            NSLog(@"%@ %@ Data was added and saved", [blockSelf class], NSStringFromSelector(_cmd));
        } else if (error) {
            NSLog(@"%@ %@ %@", [blockSelf class], NSStringFromSelector(_cmd),
                  error.description); //type macerror <errornumber> in Terminal for more info
        } else {
            NSLog(@"%@ %@ Data was added but not saved", [blockSelf class], NSStringFromSelector(_cmd));
        }
    }];
}