ios - swift 核心数据 : Failed to call designated initializer on NSManagedObject

Question

我在使用 Core Data 对象获取数据时遇到问题。

这是用于获取数据的代码

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()
        }

这是模型定义

import Foundation
import CoreData

@objc(Country)
class Country: NSManagedObject
{

.....
}

这是模型的扩展

import Foundation
import CoreData

extension Country {

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

}

我收到以下错误:

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

它在这条线上中断:

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

我不确定我是否理解这里的问题所在。有人可以建议吗？

谢谢!

Answer 1

分别去掉这两行中的感叹号即可

var countries = [Country]()

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

NSManagedObject 对象可以用作非可选对象。

隐式展开的可选类型(带感叹号)强制对象调用具体的初始化程序，该初始化程序必须为 initWithEntity:insertIntoManagedObjectContext: