NSViewController with WKWebView and progress indicator

WebViewWithProgressIndicatorController.swift

//
//  WebViewWithProgressIndicatorController
//
//  Created by Vasily Ulianov on 29.11.16.
//  Copyright © 2016 Vasily Ulianov. All rights reserved.
//

import Cocoa
import WebKit

class WebViewWithProgressIndicatorController: NSViewController, WKNavigationDelegate {
	
	@IBOutlet weak var box: NSBox!
	@IBOutlet weak var progressIndicator: NSProgressIndicator!
	@IBOutlet weak var button: NSButton!
	weak var webView: WKWebView!
	
	var url: URL? = URL(string: "https://google.com")

	override func viewDidLoad() {
		super.viewDidLoad()
		// Do view setup here.
		
		addWebView()
	}
	
	override func viewDidAppear() {
		super.viewDidAppear()
		
		if let url = url {
			let request = URLRequest(url: url)
			webView.load(request)
		}
	}
	
	// MARK: - Progress Management

	override func viewWillAppear() {
		super.viewWillAppear()
		webView.addObserver(self, forKeyPath: "estimatedProgress", options: .new, context: nil)
	}
	
	override func viewWillDisappear() {
		super.viewWillDisappear()
		webView.removeObserver(self, forKeyPath: "estimatedProgress")
	}
	
	override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
		if (keyPath == "estimatedProgress") { // listen to changes and updated view
			DispatchQueue.main.async {
				self.setProgress(self.webView.estimatedProgress * 100)
			}
		}
	}
	
	fileprivate func setProgress(_ value: Double) {
		if value == 100 {
			self.progressIndicator.isHidden = true
			return
		}
		
		self.progressIndicator.isHidden = false
		self.progressIndicator.doubleValue = value
	}
	
	// MARK: -

	private func addWebView() {
		let webView = WKWebView()
		self.webView = webView
		
		webView.frame = self.box.contentView!.bounds
		webView.navigationDelegate = self
		webView.translatesAutoresizingMaskIntoConstraints = false
		
		let contentView = box.contentView!
		contentView.addSubview(webView)
		
		NSLayoutConstraint.activate([
			webView.topAnchor.constraint(equalTo: contentView.topAnchor),
			webView.leftAnchor.constraint(equalTo: contentView.leftAnchor),
			webView.rightAnchor.constraint(equalTo: contentView.rightAnchor),
			webView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor)
			])
	}

	@IBAction func buttonClicked(_ sender: NSButton) {
		exit(0)
	}
}


extension WebViewWithProgressIndicatorController {
	func webView(webView: WKWebView, didStartProvisionalNavigation navigation: WKNavigation!) {
		self.setProgress(0)
	}
	
	func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
		self.setProgress(100)
	}
}

WebViewWithProgressIndicatorController.xib

<?xml version="1.0" encoding="UTF-8"?>
<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="11542" systemVersion="16B2657" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
    <dependencies>
        <deployment identifier="macosx"/>
        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="11542"/>
        <capability name="box content view" minToolsVersion="7.0"/>
        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
    </dependencies>
    <objects>
        <customObject id="-2" userLabel="File's Owner" customClass="WebViewWithProgressIndicatorController" customModule="uFreelance" customModuleProvider="target">
            <connections>
                <outlet property="box" destination="rbp-xL-SZi" id="NOu-sg-TnR"/>
                <outlet property="button" destination="ooo-1W-XGW" id="4Si-Du-dva"/>
                <outlet property="progressIndicator" destination="rWT-HP-KWz" id="naM-Oe-JYv"/>
                <outlet property="view" destination="Hz6-mo-xeY" id="0bl-1N-x8E"/>
            </connections>
        </customObject>
        <customObject id="-1" userLabel="First Responder" customClass="FirstResponder"/>
        <customObject id="-3" userLabel="Application" customClass="NSObject"/>
        <customView id="Hz6-mo-xeY">
            <rect key="frame" x="0.0" y="0.0" width="480" height="466"/>
            <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
            <subviews>
                <box boxType="custom" title="Box" translatesAutoresizingMaskIntoConstraints="NO" id="rbp-xL-SZi">
                    <rect key="frame" x="20" y="61" width="440" height="385"/>
                    <view key="contentView" id="pDf-kR-Q4k">
                        <rect key="frame" x="1" y="1" width="438" height="383"/>
                        <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
                    </view>
                    <color key="borderColor" name="gridColor" catalog="System" colorSpace="catalog"/>
                    <color key="fillColor" red="0.88617795705795288" green="0.88633018732070923" blue="0.88616830110549927" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
                </box>
                <button verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="ooo-1W-XGW">
                    <rect key="frame" x="14" y="13" width="82" height="32"/>
                    <buttonCell key="cell" type="push" title="Cancel" bezelStyle="rounded" alignment="center" borderStyle="border" imageScaling="proportionallyDown" inset="2" id="BTq-1i-cJX">
                        <behavior key="behavior" pushIn="YES" lightByBackground="YES" lightByGray="YES"/>
                        <font key="font" metaFont="system"/>
                        <string key="keyEquivalent" base64-UTF8="YES">
Gw
</string>
                    </buttonCell>
                    <connections>
                        <action selector="buttonClicked:" target="-2" id="RNg-LW-X53"/>
                    </connections>
                </button>
                <progressIndicator wantsLayer="YES" horizontalHuggingPriority="750" verticalHuggingPriority="750" maxValue="100" bezeled="NO" controlSize="small" style="spinning" translatesAutoresizingMaskIntoConstraints="NO" id="rWT-HP-KWz">
                    <rect key="frame" x="444" y="23" width="16" height="16"/>
                </progressIndicator>
            </subviews>
            <constraints>
                <constraint firstItem="rbp-xL-SZi" firstAttribute="leading" secondItem="Hz6-mo-xeY" secondAttribute="leading" constant="20" id="Bce-Tf-fTG"/>
                <constraint firstAttribute="bottom" secondItem="ooo-1W-XGW" secondAttribute="bottom" constant="20" id="PQs-1p-ONj"/>
                <constraint firstItem="ooo-1W-XGW" firstAttribute="top" secondItem="rbp-xL-SZi" secondAttribute="bottom" constant="20" id="Pyt-la-Zgs"/>
                <constraint firstAttribute="trailing" secondItem="rWT-HP-KWz" secondAttribute="trailing" constant="20" id="YzL-gs-taH"/>
                <constraint firstAttribute="trailing" secondItem="rbp-xL-SZi" secondAttribute="trailing" constant="20" id="bcQ-Jv-Wvj"/>
                <constraint firstItem="rWT-HP-KWz" firstAttribute="centerY" secondItem="ooo-1W-XGW" secondAttribute="centerY" id="kgg-Ka-GlV"/>
                <constraint firstItem="rbp-xL-SZi" firstAttribute="top" secondItem="Hz6-mo-xeY" secondAttribute="top" constant="20" id="kwT-zZ-kTQ"/>
                <constraint firstItem="ooo-1W-XGW" firstAttribute="leading" secondItem="Hz6-mo-xeY" secondAttribute="leading" constant="20" id="lYp-pY-ysi"/>
            </constraints>
            <point key="canvasLocation" x="131" y="266"/>
        </customView>
    </objects>
</document>

any Objective-C version?

Great solution!