Swift CoreData：無法調用NSManagedObject上的指定初始化程序

Question

我在使用Core Data對象獲取數據時遇到問題。

這是一個用於讀取數據

let fetchRequest = NSFetchRequest(entityName: "Country") 

     var countries = [Country!]() 

     do { 
      countries = try self.managedObjectContext!.executeFetchRequest(fetchRequest) as! [Country!] 
     } catch { 
      // Replace this implementation with code to handle the error appropriately. 
      // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
      let nserror = error as NSError 
      NSLog("Unresolved error \(nserror), \(nserror.userInfo)") 
      abort() 
     } 

代碼這是模型定義

import Foundation 
import CoreData 

@objc(Country) 
class Country: NSManagedObject 
{ 

..... 
} 

這是模型的擴展

import Foundation 
import CoreData 

extension Country { 

    @NSManaged var countryCode: String? 
    @NSManaged var dialCode: String? 
    @NSManaged var name: String? 

} 

我收到以下錯誤：

CoreData: error: Failed to call designated initializer on NSManagedObject class 'Country' 
fatal error: unexpectedly found nil while unwrapping an Optional value 

這是打破在這條線：

countries = try self.managedObjectContext!.executeFetchRequest(fetchRequest) as! [Country!] 

我不知道，我明白這是問題。有人可以建議嗎？

謝謝！

Answer 1

只是分別除去感嘆號在這兩行

var countries = [Country]() 

countries = try self.managedObjectContext!.executeFetchRequest(fetchRequest) as! [Country] 

NSManagedObject對象可以被用作非可選的。

隱含展開可選類型（帶感嘆號）迫使對象調用它必須是initWithEntity:insertIntoManagedObjectContext: