Fix #440 Webview loading without delegate (option 2) (#443)

* Fix #440 - Improve WKWebView navigation delegate

* Fix #440 - Replace WKWebView navigation delegate by observing wkWebView.isLoading

Co-authored-by: Tieme van Veen <Tieme.vanVeen@triodos.com>
Co-authored-by: Stephen Celis <stephen@stephencelis.com>

Sources/SnapshotTesting/Common/View.swift

@@ -753,7 +753,6 @@ extension View {
     #if os(iOS) || os(macOS)
     if let wkWebView = self as? WKWebView {
       return Async<Image> { callback in
-        let delegate = NavigationDelegate()
         let work = {
           if #available(iOS 11.0, macOS 10.13, *) {
             inWindow {
@@ -762,7 +761,6 @@ extension View {
                 return
               }
               wkWebView.takeSnapshot(with: nil) { image, _ in
-                _ = delegate
                 callback(image!)
               }
             }
@@ -776,8 +774,14 @@ extension View {
         }
 
         if wkWebView.isLoading {
-          delegate.didFinish = work
-          wkWebView.navigationDelegate = delegate
+          var subscription: NSKeyValueObservation?
+          subscription = wkWebView.observe(\.isLoading, options: [.initial, .new]) { (webview, change) in
+            subscription?.invalidate()
+            subscription = nil
+            if change.newValue == false {
+              work()
+            }
+          }
         } else {
           work()
         }
@@ -796,22 +800,6 @@ extension View {
   #endif
 }
 
-#if os(iOS) || os(macOS)
-private final class NavigationDelegate: NSObject, WKNavigationDelegate {
-  var didFinish: () -> Void
-
-  init(didFinish: @escaping () -> Void = {}) {
-    self.didFinish = didFinish
-  }
-
-  func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
-    webView.evaluateJavaScript("document.readyState") { _, _ in
-      self.didFinish()
-    }
-  }
-}
-#endif
-
 #if os(iOS) || os(tvOS)
 extension UIApplication {
     static var sharedIfAvailable: UIApplication? {

Tests/SnapshotTestingTests/SnapshotTestingTests.swift

@@ -1061,6 +1061,80 @@ final class SnapshotTestingTests: XCTestCase {
     #endif
   }
 
+  #if os(iOS) || os(macOS)
+  final class ManipulatingWKWebViewNavigationDelegate: NSObject, WKNavigationDelegate {
+    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
+      webView.evaluateJavaScript("document.body.children[0].classList.remove(\"hero\")") // Change layout
+    }
+  }
+  func testWebViewWithManipulatingNavigationDelegate() throws {
+    let manipulatingWKWebViewNavigationDelegate = ManipulatingWKWebViewNavigationDelegate()
+    let webView = WKWebView()
+    webView.navigationDelegate = manipulatingWKWebViewNavigationDelegate
+
+    let fixtureUrl = URL(fileURLWithPath: String(#file), isDirectory: false)
+      .deletingLastPathComponent()
+      .appendingPathComponent("__Fixtures__/pointfree.html")
+    let html = try String(contentsOf: fixtureUrl)
+    webView.loadHTMLString(html, baseURL: nil)
+    if !ProcessInfo.processInfo.environment.keys.contains("GITHUB_WORKFLOW") {
+      assertSnapshot(
+        matching: webView,
+        as: .image(size: .init(width: 800, height: 600)),
+        named: platform
+      )
+    }
+    _ = manipulatingWKWebViewNavigationDelegate
+  }
+
+  #if os(iOS) || os(macOS)
+  func testWebViewWithRealUrl() throws {
+    let manipulatingWKWebViewNavigationDelegate = ManipulatingWKWebViewNavigationDelegate()
+    let webView = WKWebView()
+    webView.navigationDelegate = manipulatingWKWebViewNavigationDelegate
+
+    webView.load(URLRequest(url: URL(string: "https://www.pointfree.co")!))
+    if !ProcessInfo.processInfo.environment.keys.contains("GITHUB_WORKFLOW") {
+      assertSnapshot(
+        matching: webView,
+        as: .image(size: .init(width: 800, height: 600)),
+        named: platform
+      )
+    }
+    _ = manipulatingWKWebViewNavigationDelegate
+  }
+  #endif
+
+  final class CancellingWKWebViewNavigationDelegate: NSObject, WKNavigationDelegate {
+    func webView(
+      _ webView: WKWebView,
+      decidePolicyFor navigationAction: WKNavigationAction,
+      decisionHandler: @escaping (WKNavigationActionPolicy) -> Void
+    ) {
+      decisionHandler(.cancel)
+    }
+  }
+  func testWebViewWithCancellingNavigationDelegate() throws {
+    let cancellingWKWebViewNavigationDelegate = CancellingWKWebViewNavigationDelegate()
+    let webView = WKWebView()
+    webView.navigationDelegate = cancellingWKWebViewNavigationDelegate
+
+    let fixtureUrl = URL(fileURLWithPath: String(#file), isDirectory: false)
+      .deletingLastPathComponent()
+      .appendingPathComponent("__Fixtures__/pointfree.html")
+    let html = try String(contentsOf: fixtureUrl)
+    webView.loadHTMLString(html, baseURL: nil)
+    if !ProcessInfo.processInfo.environment.keys.contains("GITHUB_WORKFLOW") {
+      assertSnapshot(
+        matching: webView,
+        as: .image(size: .init(width: 800, height: 600)),
+        named: platform
+      )
+    }
+    _ = cancellingWKWebViewNavigationDelegate
+  }
+  #endif
+
   @available(iOS 13.0, *)
   func testSwiftUIView_iOS() {
     #if os(iOS)