Project4-WKWebView, WKNavigationDelegate, KVO, @esacping

1.利用WKWebView在app内嵌入网页
在loadView()中设置view

override func loadView() {
    webView = WKWebView()
    webView.navigationDelegate = self
    view = webView
}

2.加载页面方法

let url = URL(string: "https://www.baidu.com")!
webView.load(URLRequest(url: url))
//允许右滑返回的手势
webView.allowsBackForwardNavigationGestures = true 

3.WKNavigationDelegate
页面跳转的代理方法

//发送请求之前决定是否跳转
optional public func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Swift.Void)
//收到响应之后决定是否跳转
optional public func webView(_ webView: WKWebView, decidePolicyFor navigationResponse: WKNavigationResponse, decisionHandler: @escaping (WKNavigationResponsePolicy) -> Swift.Void)
// 接收到服务器跳转请求之后调用
optional public func webView(_ webView: WKWebView, didReceiveServerRedirectForProvisionalNavigation navigation: WKNavigation!)

加载的状态回调

//页面开始加载时候调用
optional public func webView(_ webView: WKWebView, didStartProvisionalNavigation navigation: WKNavigation!)
//页面内容开始返回的时候调用
optional public func webView(_ webView: WKWebView, didCommit navigation: WKNavigation!)
//加载完成后调用
optional public func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!)
//加载失败后调用
optional public func webView(_ webView: WKWebView, didFail navigation: WKNavigation!, withError error: Error)

4.利用KVO监测webView加载的进度
添加观察器

webView.addObserver(self, forKeyPath: #keyPath(WKWebView.estimatedProgress), options: .new, context: nil)

实现监测方法

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if keyPath == #keyPath(WKWebView.estimatedProgress) {
        progressView.progress = Float(webView.estimatedProgress)
    }
}

移除观察器

deinit {
        webView.removeObserver(self, forKeyPath: #keyPath(WKWebView.estimatedProgress))
    }

5. @escaping 和@noesacpe注解

func hostFunc(@noescape closure: () -> ()) -> Void {
    //以下编译出错, closure 被修饰后, 不能被其他异步线程捕获
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
        closure()
    }
}

@noescape字面意思是无法逃脱. 在上例中, closure 被@noescape修饰, 则声明 closure 的生命周期不能超过 hostFunc, 并且, closure不能被hostFunc中的其他闭包捕获

@escaping就是可以逃逸的意思，在当前func执行完毕的时候并不影响这个闭包的执行。

[参考文章] https://swiftunboxed.com/lang/closures-escaping-noescape-swift3/?utm_campaign=This+Week+in+Swift&utm_medium=email&utm_source=This_Week_in_Swift_101