Question

我正在尝试将协议扩展初始化程序注入现有类的指定初始化程序。如果没有覆盖类中指定的初始化程序，我认为没有办法绕过它，然后调用协议扩展初始化程序。

以下是我正在尝试的内容，特别是UIViewController类：

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值设定项，以便在框架的现有初始化过程中自动调用它？

Answer 1

你不需要来调用不同的初始化程序;你已经初始化了。此外，您不需要将self转换为MyProtocol;你已经宣布采用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，MyProtocol上的扩展是针对UIViewController，FirstViewController的超类。

因此，该方法已经注入;现在直接进入并在你已经运行的初始化程序中调用注入的方法。以下代码的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.
}

如何在指定的初始值设定项中调用协议扩展初始值设定项？

1 个答案: