WKWebView-使用WebKit载入网页

代码基于Swift4.0
官方文档对 WKWebView 描述，官方推荐我们使用WKWebView而不要使用 UIWebView
Starting in iOS 8.0 and OS X 10.10, use WKWebView to add web content to your app. Do not use UIWebView or WebView.

WKWebView特点：

1. 在性能、稳定性、功能方面有很大提升；
2. 允许JavaScript的Nitro库加载并使用（UIWebView中限制）；
3. 支持了更多的HTML5特性；
4. 高达60fps的滚动刷新率以及内置手势；
5. 将UIWebViewDelegate与UIWebView重构成了14类与3个协议

使用WKWebView的小例子

import UIKit
import WebKit

class ViewController: UIViewController{
    
    var webView: WKWebView!
    
    override func loadView() {
        //创建网页加载的偏好设置
        let prefrences = WKPreferences()
        prefrences.javaScriptEnabled = false
        
        //配置网页视图
        let webConfiguration = WKWebViewConfiguration()
        webConfiguration.preferences = prefrences
        
        webView = WKWebView(frame: .zero, configuration: webConfiguration)
        webView.navigationDelegate = self;
        view = webView
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let myURL = URL(string: "https://www.apple.com")
        let myRequest = URLRequest(url: myURL!)
        webView.load(myRequest)
    }

}

// MARK: WKNavigationDelegate
extension ViewController: WKNavigationDelegate {
    //视图开始载入的时候显示网络活动指示器
    func webView(_ webView: WKWebView, didStartProvisionalNavigation navigation: WKNavigation!) {
        UIApplication.shared.isNetworkActivityIndicatorVisible = true
    }
    
    //载入结束后，关闭网络活动指示器
    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
        UIApplication.shared.isNetworkActivityIndicatorVisible = false
    }
    
    //阻止链接被点击（.cancel 自身不加载，.allow运行加载）
    func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
        if navigationAction.navigationType == .linkActivated {
            decisionHandler(.cancel)
            
            let alertController = UIAlertController(title: "Action not allowed", message: "Tapping on links is not allowed. Sorry!", preferredStyle: .alert)
            alertController.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
            present(alertController, animated: true, completion: nil)
            return
            
        }
        
        decisionHandler(.allow)
    }
}