参考: http://www.jianshu.com/p/367952852c6d
webView.addObserver(self, forKeyPath: "estimatedProgress", options: .new, context: nil)
//
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
if ((object as AnyObject).isEqual(webView) && (keyPath == "estimatedProgress")) {
progeress!.setProgress(Float(webView.estimatedProgress), animated: true)
if(webView.estimatedProgress>=1){
progeress.isHidden = true;
progeress!.setProgress(0, animated: false);
}else{
progeress.isHidden = false;
progeress!.setProgress(Float(webView.estimatedProgress), animated: true);
}
print(webView.estimatedProgress);
}
}