覆盖 initWithEntity:insertIntoManagedObjectContext：

Question

我对 initWithEntity:insertIntoManagedObjectContext: 有点困惑。根据 Swift documentation(Two-Phase Initialization)，我应该在初始化子类的所有新属性后调用 super.init。但是当我用下面的代码这样做时，我得到了错误：

//In subclass of NSManagedObject
init(entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext?, origin: NavCoordinate, destination:NavCoordinate, city: String, averageSpeedKmPH:NSNumber, client:String)
    {
        self.origin = origin
        self.destination = destination
        self.city = city
        self.averageSpeedKmPH = averageSpeedKmPH
        self.client = client
        super.init(entity: entity, insertIntoManagedObjectContext: context)
    }

问题是我收到错误："Super.init called multiple times in initializer"

如果我先调用 super.init... 就可以了。

initWithEntity:insertIntoManagedObjectContext 的文档也说：

If you override initWithEntity:insertIntoManagedObjectContext:, you must ensure that you set self to the return value from invocation of super’s implementation, as shown in the following example:

但没有任何例子。覆盖 initWithEntity:insertIntoManagedObjectContext: 的正确方法是什么？

Answer 1

init(entity entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext?) 的文档说

You are discouraged from overriding this method—you should instead override awakeFromInsert and/or awakeFromFetch (if there is logic common to these methods, it should be factored into a third method which is invoked from both). If you do perform custom initialization in this method, you may cause problems with undo and redo operations.

正确的方法是覆盖 awakeFromInsert 而不是 init。

Answer 2

我决定先调用 insertNewObjectForEntityForName，然后在实体上调用 setup 来解决。这似乎是最好的解决方案，因为这样你就不会破坏 Swift Two-Phase Initialization 并支持核心数据撤消、重做。

let journey = NSEntityDescription.insertNewObjectForEntityForName("JourneyEntity", inManagedObjectContext: moc) as! Journey
journey.setupJourney(origin, destination: destination, city: city, averageSpeedKmPH: self.user.averageSpeedKmPH, client:client)

覆盖 initWithEntity:insertIntoManagedObjectContext：

Override initWithEntity:insertIntoManagedObjectContext:

ios

swift

core-data

initialization

nsmanagedobject