[platform_view]fix iOS platform view's focus node leakage (#124066)

[platform_view]fix iOS platform view's focus node leakage

packages/flutter/lib/src/services/platform_views.dart

@@ -1378,6 +1378,7 @@ class UiKitViewController {
   Future<void> dispose() async {
     _debugDisposed = true;
     await SystemChannels.platform_views.invokeMethod<void>('dispose', id);
+    PlatformViewsService._instance._focusCallbacks.remove(id);
   }
 }
 

packages/flutter/lib/src/widgets/platform_view.dart

@@ -503,6 +503,8 @@ class _AndroidViewState extends State<AndroidView> {
   @override
   void dispose() {
     _controller.dispose();
+    _focusNode?.dispose();
+    _focusNode = null;
     super.dispose();
   }
 
@@ -562,7 +564,9 @@ class _UiKitViewState extends State<UiKitView> {
   UiKitViewController? _controller;
   TextDirection? _layoutDirection;
   bool _initialized = false;
-  late FocusNode _focusNode;
+
+  @visibleForTesting
+  FocusNode? focusNode;
 
   static final Set<Factory<OneSequenceGestureRecognizer>> _emptyRecognizersSet =
     <Factory<OneSequenceGestureRecognizer>>{};
@@ -574,7 +578,7 @@ class _UiKitViewState extends State<UiKitView> {
       return const SizedBox.expand();
     }
     return Focus(
-      focusNode: _focusNode,
+      focusNode: focusNode,
       onFocusChange: (bool isFocused) => _onFocusChange(isFocused, controller),
       child: _UiKitPlatformView(
         controller: _controller!,
@@ -634,6 +638,9 @@ class _UiKitViewState extends State<UiKitView> {
   @override
   void dispose() {
     _controller?.dispose();
+    _controller = null;
+    focusNode?.dispose();
+    focusNode = null;
     super.dispose();
   }
 
@@ -646,7 +653,7 @@ class _UiKitViewState extends State<UiKitView> {
       creationParams: widget.creationParams,
       creationParamsCodec: widget.creationParamsCodec,
       onFocus: () {
-        _focusNode.requestFocus();
+        focusNode?.requestFocus();
       }
     );
     if (!mounted) {
@@ -656,7 +663,7 @@ class _UiKitViewState extends State<UiKitView> {
     widget.onPlatformViewCreated?.call(id);
     setState(() {
       _controller = controller;
-      _focusNode = FocusNode(debugLabel: 'UiKitView(id: $id)');
+      focusNode = FocusNode(debugLabel: 'UiKitView(id: $id)');
     });
   }
 
@@ -938,6 +945,8 @@ class _PlatformViewLinkState extends State<PlatformViewLink> {
   void dispose() {
     _controller?.dispose();
     _controller = null;
+    _focusNode?.dispose();
+    _focusNode = null;
     super.dispose();
   }
 }

packages/flutter/test/widgets/platform_view_test.dart

@@ -2150,6 +2150,34 @@ void main() {
       expect(channelArguments['platformViewId'], currentViewId + 1);
     });
 
+    testWidgets('FocusNode is disposed on UIView dispose', (WidgetTester tester) async {
+      final FakeIosPlatformViewsController viewsController = FakeIosPlatformViewsController();
+      viewsController.registerViewType('webview');
+
+      await tester.pumpWidget(
+        const Center(
+          child: SizedBox(
+            width: 200.0,
+            height: 100.0,
+            child: UiKitView(viewType: 'webview', layoutDirection: TextDirection.ltr),
+          ),
+        ),
+      );
+      // casting to dynamic is required since the state class is private.
+      // ignore: avoid_dynamic_calls, invalid_assignment
+      final FocusNode node = (tester.state(find.byType(UiKitView)) as dynamic).focusNode;
+      expect(() => ChangeNotifier.debugAssertNotDisposed(node), isNot(throwsAssertionError));
+      await tester.pumpWidget(
+        const Center(
+          child: SizedBox(
+            width: 200.0,
+            height: 100.0,
+          ),
+        ),
+      );
+      expect(() => ChangeNotifier.debugAssertNotDisposed(node), throwsAssertionError);
+    });
+
     testWidgets('UiKitView has correct semantics', (WidgetTester tester) async {
       final SemanticsHandle handle = tester.ensureSemantics();
       final int currentViewId = platformViewsRegistry.getNextPlatformViewId();