在swift中实现系统协议可选要求的通用实现最简单的方法是什么？

Question

下面是系统协议和可选要求。

public protocol WKNavigationDelegate : NSObjectProtocol {

    @available(iOS 8.0, *)
    optional func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void)
}

假设有多个ViewControllers需要实现此协议。

class ViewController1: UIViewController, WKNavigationDelegate { } // default
class ViewController2: UIViewController, WKNavigationDelegate { } // default

class ViewController3: UIViewController, WKNavigationDelegate { 

    func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
        print("Override Success!")
    }
}

有没有办法可以为这个协议提供一个默认的实现，如果它没有在ViewControllers中实现，就像我们对自定义协议一样。

extension WKNavigationDelegate {

    func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
        print("Success!") // default implementation doesn't seem to work for system protocol
    }
}

Answer 1

您可以使用缺省实现扩展基类UIViewController并使其符合系统协议WKNavigationDelegate

extension UIViewController : WKNavigationDelegate  {

    func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
        print("Success!")
    }
}

并在子类中重写它