另一种方法是使用原始函数。这样避免了必须定义两个变量。在模型编辑器中，卡被定义为Int。

Another approach is to use the primitive functions. This avoid having to define two variables. In the model editor card is defined as an Int.

class ManagedObjectSubClass : NSManagedObject
{
  enum Cards : Int
  {
    case Diamonds, Hearts
  }

   var card : Cards {
     set { 
        let primitiveValue = newValue.rawValue
        self.willChangeValueForKey("card")
        self.setPrimitiveValue(primitiveValue, forKey: "card")
        self.didChangeValueForKey("card")
     }
     get { 
        self.willAccessValueForKey("card")
        let result = self.primitiveValueForKey("card") as! Int
        self.didAccessValueForKey("card")
        return Cards(rawValue:result)!
    }
   }
 }

编辑：

可以将重复部分移至NSManagedObject的扩展名上。

The repetitive part can be moved to an extension on NSManagedObject.

func setRawValue<ValueType: RawRepresentable>(value: ValueType, forKey key: String)
{
    self.willChangeValueForKey(key)
    self.setPrimitiveValue(value.rawValue as? AnyObject, forKey: key)
    self.didChangeValueForKey(key)
}

func rawValueForKey<ValueType: RawRepresentable>(key: String) -> ValueType?
{
    self.willAccessValueForKey(key)
    let result = self.primitiveValueForKey(key) as! ValueType.RawValue
    self.didAccessValueForKey(key)
    return ValueType(rawValue:result)
}