iOS 核心数据 : error when assigning a value to an attribute

Question

这是 MyApp.xcdatamodeld，非常简单:

_

这是与实体关联的类:

class LogItem: NSManagedObject {

    @NSManaged var title: String
    @NSManaged var itemText: String
    @NSManaged var itemRank: String

}

现在这是导致错误的代码:

let newItem = NSEntityDescription.insertNewObjectForEntityForName("LogItem", inManagedObjectContext: self.managedObjectContext!) as! LogItem
newItem.title = "the title of the item"
newItem.itemText = "je suis chérif"
newItem.itemRank = "2" // this line causes an error !

最后是错误:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', 
reason: '-[MyApp.LogItem setItemRank:]: unrecognized selector sent to instance 0x155a8e30'

我做错了什么？

Answer 1

当我使用核心数据对象时，我使用以下代码行创建实体。

let logEntity = NSEntityDescription.entityForName("LogItem", inManagedObjectContext: self.managedObjectContext!)
let newItem = LogItem(entity: logEntity!, insertIntoManagedObjectCntext: self.managedObjectContext!)

newItem.title = "the title of the item"
newItem.itemText = "je suis chérif"
newItem.itemRank = "2" 

然后保存上下文。