如何在 Swift 3 中将自定义类保存为 CoreData 实体的属性？

Question

我有一个 CoreData 实体 SavedWorkout。它具有以下属性：

completionCounter 是Bool 的数组，workout 是一个名为Workout 的自定义类。

我正在像这样保存我的数据：

let saveCompletionCounter = currentCompletionCounter
let saveDate = Date() as NSDate
let saveRoutineIndex = Int16(currentWorkoutRoutine)
let saveWorkout = NSKeyedArchiver.archivedData(withRootObject: workout)

item.setValue(saveDate, forKey: "date")
item.setValue(saveWorkout, forKey: "workout")
item.setValue(saveRoutineIndex, forKey: "routineIndex")
item.setValue(saveCompletionCounter, forKey: "completionCounter")

do {
  try moc.save()
  print("save successful")
} catch {
  print("saving error")
}

其中moc 是NSManagedObjectContext 的一个实例，item 是NSManagedObject 的一个实例：

moc = appDelegate.managedObjectContext
entity = NSEntityDescription.entity(forEntityName: "SavedWorkout", in: moc)!
item = NSManagedObject(entity: entity, insertInto: moc)

根据this和this和this，我已经让我的Workout类符合NSObject和NSCoding，所以现在看起来像这样：

class Workout: NSObject, NSCoding {

  let name: String
  let imageName: String
  let routine: [WorkoutRoutine]
  let shortDescription: String

  required init?(coder aDecoder: NSCoder) {
    name = aDecoder.decodeObject(forKey: "name") as! String
    imageName = aDecoder.decodeObject(forKey: "imageName") as! String
    routine = aDecoder.decodeObject(forKey: "routine") as! [WorkoutRoutine]
    shortDescription = aDecoder.decodeObject(forKey: "shortDescription") as! String
  }

  func encode(with aCoder: NSCoder) {
    aCoder.encode(name, forKey: "name")
    aCoder.encode(imageName, forKey: "imageName")
    aCoder.encode(routine, forKey: "routine")
    aCoder.encode(shortDescription, forKey: "shortDescription")
  }

  init(name: String, imageName: String, routine: [WorkoutRoutine], shortDescription: String) {
    self.name = name
    self.imageName = imageName
    self.routine = routine
    self.shortDescription = shortDescription
  }
}

但是我总是在routine: aDecoder.decodeObject... 行收到错误。

错误提示：

NSForwarding: warning: object 0x60800002cbe0 of class 'App.WorkoutRoutine' does not implement methodSignatureForSelector: -- trouble ahead

Unrecognized selector -[FitLift.WorkoutRoutine replacementObjectForKeyedArchiver:]

为什么这给我一个错误而不是另一个Transformable 属性？如何将自定义类保存为 CoreData 实体的属性？

Answer 1

问题在于 WorkoutRoutine 本身是一个自定义类，并且由于您的错误，它不符合 NSCoding 标准，因此 aCoder.encode(routine, forKey: "routine") 并不真正知道如何对其进行编码，而 routine = aDecoder.decodeObject(forKey: "routine") as! [WorkoutRoutine] 也不知道如何解码。

并不真正相关，但请为您的编码器和编码器初始化程序尝试一种更安全的方法，因为如果编码器不包含您正在寻找的密钥（出于任何原因），强制展开可能会导致崩溃

required init?(coder aDecoder: NSCoder) {
    guard let name = aDecoder.decodeObject(forKey: "name") as? String,
        let imageName = aDecoder.decodeObject(forKey: "imageName") as? String,
        let routine = aDecoder.decodeObject(forKey: "routine") as? [WorkoutRoutine],
        let shortDescription = aDecoder.decodeObject(forKey: "shortDescription") as? String else {
            return nil
    }
    self.name = name
    self.imageName = imageName
    self.routine = routine
    self.shortDescription = shortDescription
}