[webview_flutter_wkwebview] Prevent leaking when a callback method re…

…ferences an object that references itself (#6056)

packages/webview_flutter/webview_flutter_wkwebview/example/integration_test/webview_flutter_test.dart

@@ -19,6 +19,8 @@ import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:integration_test/integration_test.dart';
 import 'package:webview_flutter_platform_interface/webview_flutter_platform_interface.dart';
+import 'package:webview_flutter_wkwebview/src/common/instance_manager.dart';
+import 'package:webview_flutter_wkwebview/src/common/weak_reference_utils.dart';
 import 'package:webview_flutter_wkwebview_example/navigation_decision.dart';
 import 'package:webview_flutter_wkwebview_example/navigation_request.dart';
 import 'package:webview_flutter_wkwebview_example/web_view.dart';
@@ -66,6 +68,27 @@ Future<void> main() async {
     expect(currentUrl, primaryUrl);
   });
 
+  testWidgets(
+      'withWeakRefenceTo allows encapsulating class to be garbage collected',
+      (WidgetTester tester) async {
+    final Completer<int> gcCompleter = Completer<int>();
+    final InstanceManager instanceManager = InstanceManager(
+      onWeakReferenceRemoved: gcCompleter.complete,
+    );
+
+    ClassWithCallbackClass? instance = ClassWithCallbackClass();
+    instanceManager.addHostCreatedInstance(instance.callbackClass, 0);
+    instance = null;
+
+    // Force garbage collection.
+    await IntegrationTestWidgetsFlutterBinding.instance
+        .watchPerformance(() async {
+      await tester.pumpAndSettle();
+    });
+
+    expect(gcCompleter.future, completion(0));
+  }, timeout: const Timeout(Duration(seconds: 10)));
+
   testWidgets('loadUrl', (WidgetTester tester) async {
     final Completer<WebViewController> controllerCompleter =
         Completer<WebViewController>();
@@ -1253,3 +1276,33 @@ class ResizableWebViewState extends State<ResizableWebView> {
     );
   }
 }
+
+class CopyableObjectWithCallback with Copyable {
+  CopyableObjectWithCallback(this.callback);
+
+  final VoidCallback callback;
+
+  @override
+  CopyableObjectWithCallback copy() {
+    return CopyableObjectWithCallback(callback);
+  }
+}
+
+class ClassWithCallbackClass {
+  ClassWithCallbackClass() {
+    callbackClass = CopyableObjectWithCallback(
+      withWeakRefenceTo(
+        this,
+        (WeakReference<ClassWithCallbackClass> weakReference) {
+          return () {
+            // Weak reference to `this` in callback.
+            // ignore: unnecessary_statements
+            weakReference;
+          };
+        },
+      ),
+    );
+  }
+
+  late final CopyableObjectWithCallback callbackClass;
+}

packages/webview_flutter/webview_flutter_wkwebview/lib/src/common/weak_reference_utils.dart

@@ -0,0 +1,34 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// Helper method for creating callbacks methods with a weak reference.
+///
+/// Example:
+/// ```
+/// final JavascriptChannelRegistry javascriptChannelRegistry = ...
+///
+/// final WKScriptMessageHandler handler = WKScriptMessageHandler(
+///   didReceiveScriptMessage: withWeakRefenceTo(
+///     javascriptChannelRegistry,
+///     (WeakReference<JavascriptChannelRegistry> weakReference) {
+///       return (
+///         WKUserContentController userContentController,
+///         WKScriptMessage message,
+///       ) {
+///         weakReference.target?.onJavascriptChannelMessage(
+///           message.name,
+///           message.body!.toString(),
+///         );
+///       };
+///     },
+///   ),
+/// );
+/// ```
+S withWeakRefenceTo<T extends Object, S extends Object>(
+  T reference,
+  S Function(WeakReference<T> weakReference) onCreate,
+) {
+  final WeakReference<T> weakReference = WeakReference<T>(reference);
+  return onCreate(weakReference);
+}

packages/webview_flutter/webview_flutter_wkwebview/lib/src/foundation/foundation.dart

@@ -8,6 +8,7 @@ import 'dart:typed_data';
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
+import 'package:webview_flutter_wkwebview/src/common/weak_reference_utils.dart';
 
 import '../common/instance_manager.dart';
 import 'foundation_api_impls.dart';
@@ -267,7 +268,19 @@ class NSObject with Copyable {
 
   final NSObjectHostApiImpl _api;
 
-  /// Informs the observing object when the value at the specified key path has changed.
+  /// Informs the observing object when the value at the specified key path has
+  /// changed.
+  ///
+  /// {@template webview_flutter_wkwebview.foundation.callbacks}
+  /// For the associated Objective-C object to be automatically garbage
+  /// collected, it is required that this Function doesn't contain a strong
+  /// reference to the encapsulating class instance. Consider using
+  /// `WeakReference` when referencing an object not received as a parameter.
+  /// Otherwise, use [NSObject.dispose] to release the associated Objective-C
+  /// object manually.
+  ///
+  /// See [withWeakRefenceTo].
+  /// {@endtemplate}
   final void Function(
     String keyPath,
     NSObject object,

packages/webview_flutter/webview_flutter_wkwebview/lib/src/web_kit/web_kit.dart

@@ -442,6 +442,8 @@ class WKScriptMessageHandler extends NSObject {
   /// Use this method to respond to a message sent from the webpage’s
   /// JavaScript code. Use the [message] parameter to get the message contents and
   /// to determine the originating web view.
+  ///
+  /// {@macro webview_flutter_wkwebview.foundation.callbacks}
   final void Function(
     WKUserContentController userContentController,
     WKScriptMessage message,
@@ -733,6 +735,8 @@ class WKUIDelegate extends NSObject {
   final WKUIDelegateHostApiImpl _uiDelegateApi;
 
   /// Indicates a new [WKWebView] was requested to be created with [configuration].
+  ///
+  /// {@macro webview_flutter_wkwebview.foundation.callbacks}
   final void Function(
     WKWebView webView,
     WKWebViewConfiguration configuration,
@@ -803,26 +807,38 @@ class WKNavigationDelegate extends NSObject {
   final WKNavigationDelegateHostApiImpl _navigationDelegateApi;
 
   /// Called when navigation is complete.
+  ///
+  /// {@macro webview_flutter_wkwebview.foundation.callbacks}
   final void Function(WKWebView webView, String? url)? didFinishNavigation;
 
   /// Called when navigation from the main frame has started.
+  ///
+  /// {@macro webview_flutter_wkwebview.foundation.callbacks}
   final void Function(WKWebView webView, String? url)?
       didStartProvisionalNavigation;
 
   /// Called when permission is needed to navigate to new content.
+  ///
+  /// {@macro webview_flutter_wkwebview.foundation.callbacks}
   final Future<WKNavigationActionPolicy> Function(
     WKWebView webView,
     WKNavigationAction navigationAction,
   )? decidePolicyForNavigationAction;
 
   /// Called when an error occurred during navigation.
+  ///
+  /// {@macro webview_flutter_wkwebview.foundation.callbacks}
   final void Function(WKWebView webView, NSError error)? didFailNavigation;
 
   /// Called when an error occurred during the early navigation process.
+  ///
+  /// {@macro webview_flutter_wkwebview.foundation.callbacks}
   final void Function(WKWebView webView, NSError error)?
       didFailProvisionalNavigation;
 
   /// Called when the web view’s content process was terminated.
+  ///
+  /// {@macro webview_flutter_wkwebview.foundation.callbacks}
   final void Function(WKWebView webView)? webViewWebContentProcessDidTerminate;
 
   @override

packages/webview_flutter/webview_flutter_wkwebview/lib/src/web_kit_webview_widget.dart

@@ -11,6 +11,7 @@ import 'package:flutter/services.dart';
 import 'package:path/path.dart' as path;
 import 'package:webview_flutter_platform_interface/webview_flutter_platform_interface.dart';
 
+import 'common/weak_reference_utils.dart';
 import 'foundation/foundation.dart';
 import 'web_kit/web_kit.dart';
 
@@ -114,58 +115,74 @@ class WebKitWebViewPlatformController extends WebViewPlatformController {
 
   /// Used to integrate custom user interface elements into web view interactions.
   @visibleForTesting
-  late final WKUIDelegate uiDelegate =
-      webViewProxy.createUIDelgate(onCreateWebView: (
-    WKWebView webView,
-    WKWebViewConfiguration configuration,
-    WKNavigationAction navigationAction,
-  ) {
-    if (!navigationAction.targetFrame.isMainFrame) {
-      webView.loadRequest(navigationAction.request);
-    }
-  });
+  late final WKUIDelegate uiDelegate = webViewProxy.createUIDelgate(
+    onCreateWebView: (
+      WKWebView webView,
+      WKWebViewConfiguration configuration,
+      WKNavigationAction navigationAction,
+    ) {
+      if (!navigationAction.targetFrame.isMainFrame) {
+        webView.loadRequest(navigationAction.request);
+      }
+    },
+  );
 
   /// Methods for handling navigation changes and tracking navigation requests.
   @visibleForTesting
-  late final WKNavigationDelegate navigationDelegate =
-      webViewProxy.createNavigationDelegate(
-    didFinishNavigation: (WKWebView webView, String? url) {
-      callbacksHandler.onPageFinished(url ?? '');
-    },
-    didStartProvisionalNavigation: (WKWebView webView, String? url) {
-      callbacksHandler.onPageStarted(url ?? '');
-    },
-    decidePolicyForNavigationAction: (
-      WKWebView webView,
-      WKNavigationAction action,
-    ) async {
-      if (!_hasNavigationDelegate) {
-        return WKNavigationActionPolicy.allow;
-      }
+  late final WKNavigationDelegate navigationDelegate = withWeakRefenceTo(
+    this,
+    (WeakReference<WebKitWebViewPlatformController> weakReference) {
+      return webViewProxy.createNavigationDelegate(
+        didFinishNavigation: (WKWebView webView, String? url) {
+          weakReference.target?.callbacksHandler.onPageFinished(url ?? '');
+        },
+        didStartProvisionalNavigation: (WKWebView webView, String? url) {
+          weakReference.target?.callbacksHandler.onPageStarted(url ?? '');
+        },
+        decidePolicyForNavigationAction: (
+          WKWebView webView,
+          WKNavigationAction action,
+        ) async {
+          if (weakReference.target == null) {
+            return WKNavigationActionPolicy.allow;
+          }
+
+          if (!weakReference.target!._hasNavigationDelegate) {
+            return WKNavigationActionPolicy.allow;
+          }
+
+          final bool allow =
+              await weakReference.target!.callbacksHandler.onNavigationRequest(
+            url: action.request.url,
+            isForMainFrame: action.targetFrame.isMainFrame,
+          );
 
-      final bool allow = await callbacksHandler.onNavigationRequest(
-        url: action.request.url,
-        isForMainFrame: action.targetFrame.isMainFrame,
+          return allow
+              ? WKNavigationActionPolicy.allow
+              : WKNavigationActionPolicy.cancel;
+        },
+        didFailNavigation: (WKWebView webView, NSError error) {
+          weakReference.target?.callbacksHandler.onWebResourceError(
+            _toWebResourceError(error),
+          );
+        },
+        didFailProvisionalNavigation: (WKWebView webView, NSError error) {
+          weakReference.target?.callbacksHandler.onWebResourceError(
+            _toWebResourceError(error),
+          );
+        },
+        webViewWebContentProcessDidTerminate: (WKWebView webView) {
+          weakReference.target?.callbacksHandler.onWebResourceError(
+            WebResourceError(
+              errorCode: WKErrorCode.webContentProcessTerminated,
+              // Value from https://developer.apple.com/documentation/webkit/wkerrordomain?language=objc.
+              domain: 'WKErrorDomain',
+              description: '',
+              errorType: WebResourceErrorType.webContentProcessTerminated,
+            ),
+          );
+        },
       );
-
-      return allow
-          ? WKNavigationActionPolicy.allow
-          : WKNavigationActionPolicy.cancel;
-    },
-    didFailNavigation: (WKWebView webView, NSError error) {
-      callbacksHandler.onWebResourceError(_toWebResourceError(error));
-    },
-    didFailProvisionalNavigation: (WKWebView webView, NSError error) {
-      callbacksHandler.onWebResourceError(_toWebResourceError(error));
-    },
-    webViewWebContentProcessDidTerminate: (WKWebView webView) {
-      callbacksHandler.onWebResourceError(WebResourceError(
-        errorCode: WKErrorCode.webContentProcessTerminated,
-        // Value from https://developer.apple.com/documentation/webkit/wkerrordomain?language=objc.
-        domain: 'WKErrorDomain',
-        description: '',
-        errorType: WebResourceErrorType.webContentProcessTerminated,
-      ));
     },
   );
 
@@ -179,14 +196,23 @@ class WebKitWebViewPlatformController extends WebViewPlatformController {
       autoMediaPlaybackPolicy: params.autoMediaPlaybackPolicy,
     );
 
-    webView = webViewProxy.createWebView(configuration, observeValue: (
-      String keyPath,
-      NSObject object,
-      Map<NSKeyValueChangeKey, Object?> change,
-    ) {
-      final double progress = change[NSKeyValueChangeKey.newValue]! as double;
-      callbacksHandler.onProgress((progress * 100).round());
-    });
+    webView = webViewProxy.createWebView(
+      configuration,
+      observeValue: withWeakRefenceTo(
+        callbacksHandler,
+        (WeakReference<WebViewPlatformCallbacksHandler> weakReference) {
+          return (
+            String keyPath,
+            NSObject object,
+            Map<NSKeyValueChangeKey, Object?> change,
+          ) {
+            final double progress =
+                change[NSKeyValueChangeKey.newValue]! as double;
+            weakReference.target?.onProgress((progress * 100).round());
+          };
+        },
+      ),
+    );
 
     webView.setUIDelegate(uiDelegate);
 
@@ -413,15 +439,22 @@ class WebKitWebViewPlatformController extends WebViewPlatformController {
       ).map<Future<void>>(
         (String channelName) {
           final WKScriptMessageHandler handler =
-              webViewProxy.createScriptMessageHandler(didReceiveScriptMessage: (
-            WKUserContentController userContentController,
-            WKScriptMessage message,
-          ) {
-            javascriptChannelRegistry.onJavascriptChannelMessage(
-              message.name,
-              message.body!.toString(),
-            );
-          });
+              webViewProxy.createScriptMessageHandler(
+            didReceiveScriptMessage: withWeakRefenceTo(
+              javascriptChannelRegistry,
+              (WeakReference<JavascriptChannelRegistry> weakReference) {
+                return (
+                  WKUserContentController userContentController,
+                  WKScriptMessage message,
+                ) {
+                  weakReference.target?.onJavascriptChannelMessage(
+                    message.name,
+                    message.body!.toString(),
+                  );
+                };
+              },
+            ),
+          );
           _scriptMessageHandlers[channelName] = handler;
 
           final String wrapperSource =
@@ -652,11 +685,7 @@ class WebViewWidgetProxy {
 
   /// Constructs a [WKNavigationDelegate].
   WKNavigationDelegate createNavigationDelegate({
-    void Function(
-      WKWebView webView,
-      String? url,
-    )?
-        didFinishNavigation,
+    void Function(WKWebView webView, String? url)? didFinishNavigation,
     void Function(WKWebView webView, String? url)?
         didStartProvisionalNavigation,
     Future<WKNavigationActionPolicy> Function(