SwiftUI Webview with a Progress Bar

Webview.swift

struct Webview: UIViewControllerRepresentable {
	let url: URL

	func makeUIViewController(context: Context) -> WebviewController {
		let webviewController = WebviewController()

		let request = URLRequest(url: self.url, cachePolicy: .returnCacheDataElseLoad)
		webviewController.webview.load(request)

		return webviewController
	}

	func updateUIViewController(_ webviewController: WebviewController, context: Context) {
		//
	}
}

class WebviewController: UIViewController, WKNavigationDelegate {
	lazy var webview: WKWebView = WKWebView()
	lazy var progressbar: UIProgressView = UIProgressView()

	deinit {
		self.webview.removeObserver(self, forKeyPath: "estimatedProgress")
		self.webview.scrollView.removeObserver(self, forKeyPath: "contentOffset")
	}

	override func viewDidLoad() {
		super.viewDidLoad()

		self.webview.navigationDelegate = self
		self.view.addSubview(self.webview)

		self.webview.frame = self.view.frame
		self.webview.translatesAutoresizingMaskIntoConstraints = false
		self.view.addConstraints([
			self.webview.topAnchor.constraint(equalTo: self.view.topAnchor),
			self.webview.bottomAnchor.constraint(equalTo: self.view.bottomAnchor),
			self.webview.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
			self.webview.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
		])

		self.webview.addSubview(self.progressbar)
		self.setProgressBarPosition()

		webview.scrollView.addObserver(self, forKeyPath: "contentOffset", options: .new, context: nil)

		self.progressbar.progress = 0.1
		webview.addObserver(self, forKeyPath: "estimatedProgress", options: .new, context: nil)
	}

	func setProgressBarPosition() {
		self.progressbar.translatesAutoresizingMaskIntoConstraints = false
		self.webview.removeConstraints(self.webview.constraints)
		self.webview.addConstraints([
			self.progressbar.topAnchor.constraint(equalTo: self.webview.topAnchor, constant: self.webview.scrollView.contentOffset.y * -1),
			self.progressbar.leadingAnchor.constraint(equalTo: self.webview.leadingAnchor),
			self.progressbar.trailingAnchor.constraint(equalTo: self.webview.trailingAnchor),
		])
	}

	// MARK: - Web view progress
	override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
		switch keyPath {
		case "estimatedProgress":
			if self.webview.estimatedProgress >= 1.0 {
				UIView.animate(withDuration: 0.3, animations: { () in
					self.progressbar.alpha = 0.0
				}, completion: { finished in
					self.progressbar.setProgress(0.0, animated: false)
				})
			} else {
				self.progressbar.isHidden = false
				self.progressbar.alpha = 1.0
				progressbar.setProgress(Float(self.webview.estimatedProgress), animated: true)
			}

		case "contentOffset":
			self.setProgressBarPosition()

		default:
			super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
		}
	}
}

Updated this with better constraint management, although that example looks nicer in general.