Web Views (WKWebView)

What is WKWebView?

WKWebView is a powerful web rendering engine introduced in iOS 8 as part of the WebKit framework. It allows iOS apps to display web content efficiently while offering better performance and security than the deprecated UIWebView.

1. Key Features of WKWebView

✅ Faster performance than UIWebView
✅ Supports JavaScript execution
✅ Offers enhanced security with sandboxing
✅ Allows communication between native Swift code and JavaScript
✅ Provides fine-grained control over web content

2. Adding WKWebView in Storyboard

Drag & Drop a WKWebView from the Object Library.
Set constraints to position it properly within the view.
Create an IBOutlet for the WebView in the ViewController.
Load a URL or HTML content programmatically.

3. Implementing WKWebView Programmatically

3.1 Basic Setup

import UIKit
import WebKit

class ViewController: UIViewController, WKNavigationDelegate {

    var webView: WKWebView!

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Initialize WKWebView
        webView = WKWebView(frame: view.bounds)
        webView.navigationDelegate = self
        view.addSubview(webView)

        // Load a URL
        if let url = URL(string: "https://www.apple.com") {
            let request = URLRequest(url: url)
            webView.load(request)
        }
    }
}

✅ This creates a simple WebView that loads Apple’s website.

4. Loading Different Types of Web Content

4.1 Load a URL

let url = URL(string: "https://www.example.com")!
webView.load(URLRequest(url: url))

4.2 Load Local HTML File

if let localHTMLPath = Bundle.main.path(forResource: "index", ofType: "html") {
    let localURL = URL(fileURLWithPath: localHTMLPath)
    webView.loadFileURL(localURL, allowingReadAccessTo: localURL)
}

4.3 Load HTML String

let htmlString = "<html><body><h1>Hello, WKWebView!</h1></body></html>"
webView.loadHTMLString(htmlString, baseURL: nil)

5. Handling Web Navigation with WKNavigationDelegate

To monitor navigation events, conform to the WKNavigationDelegate protocol.

5.1 Detect Page Load Start & End

func webView(_ webView: WKWebView, didStartProvisionalNavigation navigation: WKNavigation!) {
    print("Page is loading...")
}

func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
    print("Page loaded successfully!")
}

5.2 Handle Page Load Errors

func webView(_ webView: WKWebView, didFail navigation: WKNavigation!, withError error: Error) {
    print("Failed to load page: \(error.localizedDescription)")
}

6. Enabling JavaScript Execution

By default, WKWebView supports JavaScript, but additional configurations might be needed.

let webConfig = WKWebViewConfiguration()
webConfig.preferences.javaScriptEnabled = true
let webView = WKWebView(frame: .zero, configuration: webConfig)

7. Communicating Between Swift & JavaScript

7.1 Inject JavaScript into WebPage

webView.evaluateJavaScript("document.body.style.backgroundColor = 'lightgray'") { (result, error) in
    if let error = error {
        print("JavaScript Error: \(error.localizedDescription)")
    }
}

7.2 Send Data from JavaScript to Swift

1️⃣ Add a JavaScript message handler in Swift:

class ViewController: UIViewController, WKScriptMessageHandler {
    override func viewDidLoad() {
        let contentController = webView.configuration.userContentController
        contentController.add(self, name: "messageHandler")
    }
    
    func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
        print("Message from JavaScript: \(message.body)")
    }
}

2️⃣ Call the message handler from JavaScript:

window.webkit.messageHandlers.messageHandler.postMessage("Hello from JavaScript!");

✅ This enables two-way communication between Swift and JavaScript.

8. Adding Navigation Controls

8.1 Adding a Toolbar with Back & Forward Buttons

let backButton = UIBarButtonItem(title: "Back", style: .plain, target: self, action: #selector(goBack))
let forwardButton = UIBarButtonItem(title: "Forward", style: .plain, target: self, action: #selector(goForward))

@objc func goBack() {
    if webView.canGoBack {
        webView.goBack()
    }
}

@objc func goForward() {
    if webView.canGoForward {
        webView.goForward()
    }
}

9. Handling Links Inside WebView

To control how URLs open, implement WKNavigationDelegate.

func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    if let url = navigationAction.request.url, url.absoluteString.contains("external-site.com") {
        UIApplication.shared.open(url)  // Open in Safari
        decisionHandler(.cancel)
        return
    }
    decisionHandler(.allow)
}

✅ This ensures external links open in Safari while keeping internal navigation inside WKWebView.

10. Caching & Performance Optimization

10.1 Enabling Cache for Faster Loading

let cachePolicy = URLRequest.CachePolicy.returnCacheDataElseLoad
let request = URLRequest(url: URL(string: "https://example.com")!, cachePolicy: cachePolicy, timeoutInterval: 10)
webView.load(request)

10.2 Clearing WebView Cache

let dataStore = WKWebsiteDataStore.default()
dataStore.fetchDataRecords(ofTypes: WKWebsiteDataStore.allWebsiteDataTypes()) { records in
    records.forEach { dataStore.removeData(ofTypes: $0.dataTypes, for: [$0], completionHandler: {}) }
}

✅ This prevents excessive data storage and ensures fresh content loading.

11. Common Issues & Fixes

❌ Issue: WebView Not Loading URL

✅ Fix: Ensure the URL is valid and App Transport Security (ATS) allows non-HTTPS URLs.

Add this to Info.plist to allow HTTP URLs:

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsArbitraryLoads</key>
    <true/>
</dict>

❌ Issue: JavaScript Not Running

✅ Fix: Enable JavaScript in WKWebViewConfiguration.

12. Conclusion

✔️ WKWebView is the recommended way to embed web content in iOS apps.
✔️ Offers faster performance, better security, and full JavaScript support.
✔️ Provides customization options like navigation control, JavaScript execution, and message passing.
✔️ Supports modern web technologies like HTML5, CSS, and JavaScript frameworks.

Would you like a specific WKWebView feature implementation in your project? 🚀