Flush are rebuild web view queue when suspending and restoring the app. Issue #1563

iOS/Article/WebViewProvider.swift

@@ -13,6 +13,10 @@ import WebKit
 /// Keep a queue of WebViews where we've already done a trivial load so that by the time we need them in the UI, they're past the flash-to-shite part of their lifecycle.
 class WebViewProvider: NSObject, WKNavigationDelegate {
 	
+	private struct MessageName {
+		static let domContentLoaded = "domContentLoaded"
+	}
+
 	let articleIconSchemeHandler: ArticleIconSchemeHandler
 	
 	private let minimumQueueDepth = 3
@@ -26,7 +30,31 @@ class WebViewProvider: NSObject, WKNavigationDelegate {
 		articleIconSchemeHandler = ArticleIconSchemeHandler(coordinator: coordinator)
 		super.init()
 		viewController.view.insertSubview(queue, at: 0)
+		
 		replenishQueueIfNeeded()
+		
+		NotificationCenter.default.addObserver(self, selector: #selector(didEnterBackground), name: UIApplication.didEnterBackgroundNotification, object: nil)
+		NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
+	}
+	
+	@objc func didEnterBackground() {
+		flushQueue()
+	}
+
+	@objc func willEnterForeground() {
+		replenishQueueIfNeeded()
+	}
+
+	func flushQueue() {
+		queue.subviews.forEach { $0.removeFromSuperview() }
+		waitingForFirstLoad = true
+	}
+
+	func replenishQueueIfNeeded() {
+		while queue.subviews.count < minimumQueueDepth {
+			let webView = WKWebView(frame: .zero, configuration: buildConfiguration())
+			enqueueWebView(webView)
+		}
 	}
 	
 	func dequeueWebView(completion: @escaping (WKWebView) -> ()) {
@@ -42,11 +70,10 @@ class WebViewProvider: NSObject, WKNavigationDelegate {
 			return
 		}
 
-		webView.navigationDelegate = self
+		webView.configuration.userContentController.add(WrapperScriptMessageHandler(self), name: MessageName.domContentLoaded)
 		queue.insertSubview(webView, at: 0)
 
 		webView.loadFileURL(ArticleRenderer.page.url, allowingReadAccessTo: ArticleRenderer.page.baseURL)
-
 	}
 
 	// MARK: WKNavigationDelegate
@@ -63,30 +90,39 @@ class WebViewProvider: NSObject, WKNavigationDelegate {
 		}
 	}
 	
-	// MARK: Private
+}
 
-	private func replenishQueueIfNeeded() {
-		while queue.subviews.count < minimumQueueDepth {
-			let preferences = WKPreferences()
-			preferences.javaScriptCanOpenWindowsAutomatically = false
-			preferences.javaScriptEnabled = true
+// MARK: WKScriptMessageHandler
 
-			let configuration = WKWebViewConfiguration()
-			configuration.preferences = preferences
-			configuration.setValue(true, forKey: "allowUniversalAccessFromFileURLs")
-			configuration.allowsInlineMediaPlayback = true
-			configuration.mediaTypesRequiringUserActionForPlayback = .video
-			configuration.setURLSchemeHandler(articleIconSchemeHandler, forURLScheme: ArticleRenderer.imageIconScheme)
-			
-			let webView = WKWebView(frame: .zero, configuration: configuration)
-			enqueueWebView(webView)
+extension WebViewProvider: WKScriptMessageHandler {
+
+	func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
+		switch message.name {
+		case MessageName.domContentLoaded:
+			if waitingForFirstLoad {
+				waitingForFirstLoad = false
+				if let completion = waitingCompletionHandler {
+					DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
+						self.completeRequest(completion: completion)
+						self.waitingCompletionHandler = nil
+					}
+				}
+			}
+		default:
+			return
 		}
 	}
 	
-	private func completeRequest(completion: @escaping (WKWebView) -> ()) {
+}
+
+// MARK: Private
+
+private extension WebViewProvider {
+	
+	func completeRequest(completion: @escaping (WKWebView) -> ()) {
 		if let webView = queue.subviews.last as? WKWebView {
 			webView.removeFromSuperview()
-			webView.navigationDelegate = nil
+			webView.configuration.userContentController.removeScriptMessageHandler(forName: MessageName.domContentLoaded)
 			replenishQueueIfNeeded()
 			completion(webView)
 			return
@@ -96,5 +132,19 @@ class WebViewProvider: NSObject, WKNavigationDelegate {
 		let webView = WKWebView(frame: .zero)
 		completion(webView)
 	}
-	
+
+	func buildConfiguration() -> WKWebViewConfiguration {
+		let preferences = WKPreferences()
+		preferences.javaScriptCanOpenWindowsAutomatically = false
+		preferences.javaScriptEnabled = true
+
+		let configuration = WKWebViewConfiguration()
+		configuration.preferences = preferences
+		configuration.setValue(true, forKey: "allowUniversalAccessFromFileURLs")
+		configuration.allowsInlineMediaPlayback = true
+		configuration.mediaTypesRequiringUserActionForPlayback = .video
+		configuration.setURLSchemeHandler(articleIconSchemeHandler, forURLScheme: ArticleRenderer.imageIconScheme)
+		
+		return configuration
+	}
 }