UIWebView(WKWebViewではない！)を利用している画面で、スクロールに応じてナビゲーションバー/ツールバーを
表示/非表示にする機会があったのでメモ

##パターン1

hidesBarsOnSwipeをtrueにセットするだけでOK
ただし、私の環境(iOS11.3)において、UIWebViewでこれを利用してもアニメーションがおかしくなった...

override func viewDidLoad() {

	self.navigationController?.setNavigationBarHidden(false, animated: true)
	self.navigationController?.setToolbarHidden(false, animated: true)
	self.navigationController?.hidesBarsOnSwipe = true
}

##パターン2

UIWebViewにUIScrollViewDelegateをセット
scroll位置を取得し、移動量に従ってsetToolbarHidden/setNavigationBarHiddenにtrue/falseを設定する

override func viewDidLoad() {

	self.navigationController?.setNavigationBarHidden(false, animated: true)
	self.navigationController?.setToolbarHidden(false, animated: true)
	webview?.scrollView.delegate = self
}

extension MyViewController: UIScrollViewDelegate {
    
    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        scrollBeginPoint = scrollView.contentOffset
    }
    
    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        let scrollEndPoint = scrollView.contentOffset

        if isBarShowing == true && scrollBeginPoint.y < scrollEndPoint.y {
            self.navigationController?.setToolbarHidden(true, animated: true)
            self.navigationController?.setNavigationBarHidden(true, animated: true)
            isBarShowing = false
        } else if isBarShowing == false && scrollBeginPoint.y > scrollEndPoint.y{
            self.navigationController?.setToolbarHidden(false, animated: true)
            self.navigationController?.setNavigationBarHidden(false, animated: true)
            isBarShowing = true
        }
    }
}

##パターン3

scrollから値をとるのではなく、Gestureで判定したものから移動量に従ってsetToolbarHidden/setNavigationBarHiddenにtrue/falseを設定する

class MyViewController: UIViewController {
	
	var isBarShowing = true

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let upSwipe = UISwipeGestureRecognizer(target: self, action: #selector(didUpSwipe(_:)))
        upSwipe.direction = .up
        upSwipe.delegate = self
        let downSwipe = UISwipeGestureRecognizer(target: self, action: #selector(didDownSwipe(_:)))
        downSwipe.direction = .down
        downSwipe.delegate = self
        self.view.addGestureRecognizer(upSwipe)
        self.view.addGestureRecognizer(downSwipe)
    }

    @objc func didUpSwipe(_ sender: UITapGestureRecognizer) {
        if isBarShowing {
            self.navigationController?.setToolbarHidden(true, animated: true)
            self.navigationController?.setNavigationBarHidden(true, animated: true)
            isBarShowing = false
        }
    }
    
    @objc func didDownSwipe(_ sender: UITapGestureRecognizer) {
        if !isBarShowing {
            self.navigationController?.setToolbarHidden(false, animated: true)
            self.navigationController?.setNavigationBarHidden(false, animated: true)
            isBarShowing = true
        }
    }