WKWebview--透明背景，自适应高度，禁用长按选择和缩放：
// WebView didFinish loading
func webView(_webView:WKWebView, didFinish navigation:WKNavigation!) {
1. 自适应高度：
webView.evaluateJavaScript("document.body.scrollHeight") {[weakself] result,_in
if let tempHeight:Double= resultas?Double{
self?.maximumHeightConstraint.constant=CGFloat(tempHeight)
}
}
2. 禁用缩放功能：
let jsForbiddenZooming = "var script = document.createElement('meta');script.name = 'viewport';script.content='width=device-width, initial-scale=1.0,maximum-scale=1.0, minimum-scale=1.0, user-scalable=no';document.getElementsByTagName('head')[0].appendChild(script);"
webView.evaluateJavaScript(jsForbiddenZooming, completionHandler:nil)
3. 禁用长按选择和复制功能：
webView.evaluateJavaScript("document.documentElement.style.webkitTouchCallout='none';", completionHandler: nil)
webView.evaluateJavaScript("document.documentElement.style.webkitUserSelect='none';", completionHandler: nil)
}
########################
// viewDidLoad()
override func viewDidLoad() {
super.viewDidLoad()
1. 透明背景
webView.isOpaque = false
webView.backgroundColor = .clear
webView.scrollView.backgroundColor = .clear
2. 解决 webview内容下移的问题：
if #available(iOS 11.0, *) {
webView.scrollView.contentInsetAdjustmentBehavior = .never
}else{
self.automaticallyAdjustsScrollViewInsets = false
}
}
