[webview_flutter_android] Fix the leak in the legacy implementation

packages/webview_flutter/webview_flutter_android/example/integration_test/legacy/webview_flutter_test.dart

@@ -18,6 +18,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:integration_test/integration_test.dart';
+import 'package:webview_flutter_android/src/android_webview.dart' as android;
+import 'package:webview_flutter_android/src/android_webview_api_impls.dart';
 import 'package:webview_flutter_android/src/instance_manager.dart';
 import 'package:webview_flutter_android/src/weak_reference_utils.dart';
 import 'package:webview_flutter_android/src/webview_flutter_android_legacy.dart';
@@ -126,6 +128,76 @@ Future<void> main() async {
     expect(gcIdentifier, 0);
   }, timeout: const Timeout(Duration(seconds: 10)));
 
+  testWidgets(
+    'WebView is released by garbage collection',
+    (WidgetTester tester) async {
+      final Completer<void> webViewGCCompleter = Completer<void>();
+
+      late final InstanceManager instanceManager;
+      instanceManager =
+          InstanceManager(onWeakReferenceRemoved: (int identifier) {
+        final Copyable instance =
+            instanceManager.getInstanceWithWeakReference(identifier)!;
+        if (instance is android.WebView && !webViewGCCompleter.isCompleted) {
+          webViewGCCompleter.complete();
+        }
+      });
+
+      android.WebView.api = WebViewHostApiImpl(
+        instanceManager: instanceManager,
+      );
+      android.WebSettings.api = WebSettingsHostApiImpl(
+        instanceManager: instanceManager,
+      );
+      android.WebChromeClient.api = WebChromeClientHostApiImpl(
+        instanceManager: instanceManager,
+      );
+      android.WebViewClient.api = WebViewClientHostApiImpl(
+        instanceManager: instanceManager,
+      );
+      android.DownloadListener.api = DownloadListenerHostApiImpl(
+        instanceManager: instanceManager,
+      );
+
+      // Continually recreate web views until one is disposed through garbage
+      // collection.
+      while (!webViewGCCompleter.isCompleted) {
+        await tester.pumpWidget(
+          Builder(
+            builder: (BuildContext context) {
+              return AndroidWebView(instanceManager: instanceManager).build(
+                context: context,
+                creationParams: CreationParams(
+                  webSettings: WebSettings(
+                    hasNavigationDelegate: false,
+                    userAgent: const WebSetting<String>.of('woeifj'),
+                  ),
+                ),
+                javascriptChannelRegistry: JavascriptChannelRegistry(
+                  <JavascriptChannel>{},
+                ),
+                webViewPlatformCallbacksHandler: TestPlatformCallbacksHandler(),
+              );
+            },
+          ),
+        );
+        await tester.pumpAndSettle();
+
+        await tester.pumpWidget(Container());
+        await tester.pumpAndSettle();
+      }
+
+      android.WebView.api = WebViewHostApiImpl();
+      android.WebSettings.api = WebSettingsHostApiImpl();
+      android.WebChromeClient.api = WebChromeClientHostApiImpl();
+      android.WebViewClient.api = WebViewClientHostApiImpl();
+      android.DownloadListener.api = DownloadListenerHostApiImpl();
+
+      // Create a new `WebStorage` with the default InstanceManager.
+      android.WebStorage.instance = android.WebStorage();
+    },
+  );
+
   testWidgets('evaluateJavascript', (WidgetTester tester) async {
     final Completer<WebViewController> controllerCompleter =
         Completer<WebViewController>();
@@ -1572,3 +1644,25 @@ class ClassWithCallbackClass {
 
   late final CopyableObjectWithCallback callbackClass;
 }
+
+class TestPlatformCallbacksHandler implements WebViewPlatformCallbacksHandler {
+  @override
+  FutureOr<bool> onNavigationRequest({
+    required String url,
+    required bool isForMainFrame,
+  }) async {
+    return true;
+  }
+
+  @override
+  void onPageStarted(String url) {}
+
+  @override
+  void onPageFinished(String url) {}
+
+  @override
+  void onProgress(int progress) {}
+
+  @override
+  void onWebResourceError(WebResourceError error) {}
+}

packages/webview_flutter/webview_flutter_android/lib/src/legacy/webview_android.dart

@@ -12,6 +12,7 @@ import 'package:flutter/widgets.dart';
 import 'package:webview_flutter_platform_interface/src/webview_flutter_platform_interface_legacy.dart';
 
 import '../android_webview.dart';
+import '../instance_manager.dart';
 import 'webview_android_widget.dart';
 
 /// Builds an Android webview.
@@ -20,6 +21,15 @@ import 'webview_android_widget.dart';
 /// an [AndroidView] to embed the webview in the widget hierarchy, and uses a method channel to
 /// communicate with the platform code.
 class AndroidWebView implements WebViewPlatform {
+  /// Constructs an [AndroidWebView].
+  AndroidWebView({@visibleForTesting InstanceManager? instanceManager})
+      : instanceManager = instanceManager ?? JavaObject.globalInstanceManager;
+
+  /// Maintains instances used to communicate with the native objects they
+  /// represent.
+  @protected
+  final InstanceManager instanceManager;
+
   @override
   Widget build({
     required BuildContext context,
@@ -55,8 +65,7 @@ class AndroidWebView implements WebViewPlatform {
             gestureRecognizers: gestureRecognizers,
             layoutDirection:
                 Directionality.maybeOf(context) ?? TextDirection.rtl,
-            creationParams: JavaObject.globalInstanceManager
-                .getIdentifier(controller.webView),
+            creationParams: instanceManager.getIdentifier(controller.webView),
             creationParamsCodec: const StandardMessageCodec(),
           ),
         );

packages/webview_flutter/webview_flutter_android/lib/src/legacy/webview_android_widget.dart

@@ -138,16 +138,26 @@ class WebViewAndroidPlatformController extends WebViewPlatformController {
   final Map<String, WebViewAndroidJavaScriptChannel> _javaScriptChannels =
       <String, WebViewAndroidJavaScriptChannel>{};
 
-  late final android_webview.WebViewClient _webViewClient = withWeakReferenceTo(
-      this, (WeakReference<WebViewAndroidPlatformController> weakReference) {
-    return webViewProxy.createWebViewClient(
-      onPageStarted: (_, String url) {
+  late final android_webview.WebViewClient _webViewClient =
+      webViewProxy.createWebViewClient(
+    onPageStarted: withWeakReferenceTo(this, (
+      WeakReference<WebViewAndroidPlatformController> weakReference,
+    ) {
+      return (_, String url) {
         weakReference.target?.callbacksHandler.onPageStarted(url);
-      },
-      onPageFinished: (_, String url) {
+      };
+    }),
+    onPageFinished: withWeakReferenceTo(this, (
+      WeakReference<WebViewAndroidPlatformController> weakReference,
+    ) {
+      return (_, String url) {
         weakReference.target?.callbacksHandler.onPageFinished(url);
-      },
-      onReceivedError: (
+      };
+    }),
+    onReceivedError: withWeakReferenceTo(this, (
+      WeakReference<WebViewAndroidPlatformController> weakReference,
+    ) {
+      return (
         _,
         int errorCode,
         String description,
@@ -160,8 +170,12 @@ class WebViewAndroidPlatformController extends WebViewPlatformController {
           failingUrl: failingUrl,
           errorType: _errorCodeToErrorType(errorCode),
         ));
-      },
-      onReceivedRequestError: (
+      };
+    }),
+    onReceivedRequestError: withWeakReferenceTo(this, (
+      WeakReference<WebViewAndroidPlatformController> weakReference,
+    ) {
+      return (
         _,
         android_webview.WebResourceRequest request,
         android_webview.WebResourceError error,
@@ -175,21 +189,29 @@ class WebViewAndroidPlatformController extends WebViewPlatformController {
             errorType: _errorCodeToErrorType(error.errorCode),
           ));
         }
-      },
-      urlLoading: (_, String url) {
+      };
+    }),
+    urlLoading: withWeakReferenceTo(this, (
+      WeakReference<WebViewAndroidPlatformController> weakReference,
+    ) {
+      return (_, String url) {
         weakReference.target?._handleNavigationRequest(
           url: url,
           isForMainFrame: true,
         );
-      },
-      requestLoading: (_, android_webview.WebResourceRequest request) {
+      };
+    }),
+    requestLoading: withWeakReferenceTo(this, (
+      WeakReference<WebViewAndroidPlatformController> weakReference,
+    ) {
+      return (_, android_webview.WebResourceRequest request) {
         weakReference.target?._handleNavigationRequest(
           url: request.url,
           isForMainFrame: request.isForMainFrame,
         );
-      },
-    );
-  });
+      };
+    }),
+  );
 
   bool _hasNavigationDelegate = false;
   bool _hasProgressTracking = false;

packages/webview_flutter/webview_flutter_android/lib/src/legacy/webview_surface_android.dart

@@ -30,6 +30,9 @@ import 'webview_android_widget.dart';
 /// https://github.com/flutter/flutter/wiki/Hybrid-Composition for more
 /// information.
 class SurfaceAndroidWebView extends AndroidWebView {
+  /// Constructs a [SurfaceAndroidWebView].
+  SurfaceAndroidWebView({@visibleForTesting super.instanceManager});
+
   @override
   Widget build({
     required BuildContext context,
@@ -74,8 +77,8 @@ class SurfaceAndroidWebView extends AndroidWebView {
               // directionality.
               layoutDirection:
                   Directionality.maybeOf(context) ?? TextDirection.ltr,
-              webViewIdentifier: JavaObject.globalInstanceManager
-                  .getIdentifier(controller.webView)!,
+              webViewIdentifier:
+                  instanceManager.getIdentifier(controller.webView)!,
             )
               ..addOnPlatformViewCreatedListener(params.onPlatformViewCreated)
               ..addOnPlatformViewCreatedListener((int id) {