ios - NSManagedObject 不能符合 Swift 中的协议(protocol)

Question

我需要一个 NSManagedObject 和一个常规 NSObject 的共享接口(interface)。在 Objective-c 中，我可以使用一个协议(protocol)来实现它。但是在 Swift 中我得到了这个运行时错误。任何解决方案？提前致谢!

protocol Product {
    var code: String { get set }
    var sp: String { get set }
}

class Stock: NSManagedObject, Product {
    @NSManaged var code: String
    @NSManaged var sp: String
}

Error: Undefined symbols for architecture i386: "__TFC11YellowPages5Stockg2spSS", referenced from: __TFC11YellowPages5Stockm2spSS in Stock.o "__TFC11YellowPages5Stockg4codeSS", referenced from: __TFC11YellowPages5Stockm4codeSS in Stock.o ld: symbol(s) not found for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation)

Answer 1

这对我有用。亲自尝试一下，看看是否有效:

class MyEntity: NSManagedObject {

    @NSManaged var testAttribute: String
}

@objc
protocol MyProtocol {

    var testAttribute: String { get set }
}

extension MyEntity: MyProtocol { }

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
        let myContext = appDelegate.managedObjectContext!
        let entity: MyEntity = NSEntityDescription.insertNewObjectForEntityForName("MyEntity", inManagedObjectContext: myContext) as MyEntity
        foo(entity)
        println(entity.testAttribute)
    }

    func foo(var object: MyProtocol) {
        object.testAttribute = "bar"
    }
}

下面的方法也有效，但我认为上面的方法更好:

@objc
protocol MyProtocol {

    var testAttribute: String { get set }
}

class MyEntity: NSManagedObject, MyProtocol {

    @NSManaged var testAttribute: String
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
        let myContext = appDelegate.managedObjectContext!
        let entity: MyEntity = NSEntityDescription.insertNewObjectForEntityForName("MyEntity", inManagedObjectContext: myContext) as MyEntity
        foo(entity)
        println(entity.testAttribute)
    }

    func foo(var object: MyProtocol) {
        object.testAttribute = "bar"
    }
}