如何在指定初始化器中调用协议扩展初始化器？

Question

我正在尝试将协议扩展初始化程序注入现有 class 的指定初始化程序。我不认为有什么办法可以解决这个问题，除非覆盖 class 中的指定初始化程序，然后在其中调用协议扩展初始化程序。

下面是我正在尝试的，特别是 UIViewController class:

class FirstViewController: UIViewController, MyProtocol {

    var locationManager: CLLocationManager?
    var lastRendered: NSDate?

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        // TODO: How to call MyProtocol initializer?
        // (self as MyProtocol).init(aDecoder) // Didn't compile
    }

}

protocol MyProtocol: CLLocationManagerDelegate {

    var locationManager: CLLocationManager? { get set }
    var lastRendered: NSDate? { get set }

    init?(coder aDecoder: NSCoder)
}

extension MyProtocol where Self: UIViewController {

    // Possible to inject this into initialization process?
    init?(coder aDecoder: NSCoder) {
        self.init(coder: aDecoder)
        setupLocationManager()
    }

    func setupLocationManager() {
        locationManager = CLLocationManager()
        locationManager?.delegate = self
        locationManager?.desiredAccuracy = kCLLocationAccuracyThreeKilometers
        locationManager?.distanceFilter = 1000.0
        locationManager?.startUpdatingLocation()
    }

    func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        // TODO
    }

    func locationManager(manager: CLLocationManager, didChangeAuthorizationStatus status: CLAuthorizationStatus) {
        // TODO
    }

    func locationManager(manager: CLLocationManager, didFailWithError error: NSError) {
        // TODO
    }
}

有没有办法利用协议扩展初始化程序，以便在框架的现有初始化过程中自动调用它？

Answer 1

您不需要调用不同的初始化程序；你已经在初始化了。此外，您不需要将 self 转换为 MyProtocol；您已经声明它采用 MyProtocol。另外，你已经将 MyProtocol 的 setupLocationManager 注入到 FirstViewController 中，因为你的 FirstViewController 已经采用了 MyProtocol 并且 MyProtocol 上的扩展针对的是 UIViewController，FirstViewController 的超类。

所以，这个方法已经被注入了；现在就直接在初始化程序中调用注入的方法，您已经运行。您的代码的以下精简版本编译得非常好：

class FirstViewController: UIViewController, MyProtocol {
    var locationManager: CLLocationManager?

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.setupLocationManager() // no problem!
    }
}

protocol MyProtocol: CLLocationManagerDelegate {
    // this next line is necessary so that
    // ...setupLocationManager can refer to `self.locationManager`
    var locationManager: CLLocationManager? { get set }
}

extension MyProtocol where Self: UIViewController {
    func setupLocationManager() {
        locationManager = CLLocationManager()
        // ... etc.
    }
    // ... etc.
}

如何在指定初始化器中调用协议扩展初始化器？

How to call protocol extensions initializers in designated initializers?

swift

class

swift2

designated-initializer

protocol-extension