WKWebView delegate的歧义方法

Question

我创建了一个名为JSBridge的类，这个类实现了WKNavigationDelegate，我在协议方法中做了一些自定义的东西，然后调用另一个UIViewController的默认WKNavigationDelegate，例如WebViewController又名webViewDelegate，所以我必须这样做

func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    guard let webViewDelegate = webViewDelegate , self.webView == webView else {
        decisionHandler(.allow)
        return
    }
    //do something here then call `WebViewController`'s implementation
    if webViewDelegate.responds(to: #selector(webViewDelegate.webView(_:decidePolicyFor:decisionHandler:))) {
            webViewDelegate.webView!(webView, decidePolicyFor: navigationAction, decisionHandler: decisionHandler)
        } else {
            decisionHandler(.allow)
        }
}
func webView(_ webView: WKWebView, decidePolicyFor navigationResponse: WKNavigationResponse, decisionHandler: @escaping (WKNavigationResponsePolicy) -> Void) {
    guard let webViewDelegate = webViewDelegate , self.webView == webView else {
        decisionHandler(.allow)
        return
    }
    //do something here then 
    if webViewDelegate.responds(to: #selector(webViewDelegate.webView(_:decidePolicyFor:decisionHandler:))) {
        webViewDelegate.webView!(webView, decidePolicyFor: navigationResponse, decisionHandler: decisionHandler)
    } else {
        decisionHandler(.allow)
    }
}

我的问题是在xcode8(swift3)编译器给我的错误:Ambiguous use of 'webView(_:decidePolicyFor:decisionHandler:)'，它们与编译器同名

func webView(_ webView: WKWebView, decidePolicyFor navigationResponse: WKNavigationResponse, decisionHandler: @escaping (WKNavigationResponsePolicy) -> Void)
func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void)

Answer 1

您可以使用as从一些模棱两可的方法中选择一个:

func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    guard let webViewDelegate = webViewDelegate , self.webView == webView else {
        decisionHandler(.allow)
        return
    }
    typealias WKNavigationActionMethodType = (WKWebView,WKNavigationAction,@escaping(WKNavigationActionPolicy)->Void) -> Void
    if webViewDelegate.responds(to: #selector(webView(_:decidePolicyFor:decisionHandler:) as WKNavigationActionMethodType)) {
        webViewDelegate.webView!(webView, decidePolicyFor: navigationAction, decisionHandler: decisionHandler)
    } else {
        decisionHandler(.allow)
    }
}

---

处理这种情况的另一种方法是"避免使用responds(to:)并使用可选链接":

func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    guard let webViewDelegate = webViewDelegate , self.webView == webView else {
        decisionHandler(.allow)
        return
    }
    if webViewDelegate.webView?(webView, decidePolicyFor: navigationAction, decisionHandler: decisionHandler) == nil {
        decisionHandler(.allow)
    }
}

委托方法的返回类型是Void，所以它的可选链接结果的类型是Void?。在您的示例中，只有当可选方法没有在实例中实现时，它才变为nil。因此，将结果与nil进行比较是检查可选方法是否实现(并实际调用)。