Add Focus support for iOS platform view (#103019)

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

@@ -199,6 +199,8 @@ class PlatformViewsService {
   /// factory for this view type must have been registered on the platform side.
   /// Platform view factories are typically registered by plugin code.
   ///
+  /// `onFocus` is a callback that will be invoked when the UIKit view asks to
+  /// get the input focus.
   /// The `id, `viewType, and `layoutDirection` parameters must not be null.
   /// If `creationParams` is non null then `creationParamsCodec` must not be null.
   static Future<UiKitViewController> initUiKitView({
@@ -207,6 +209,7 @@ class PlatformViewsService {
     required TextDirection layoutDirection,
     dynamic creationParams,
     MessageCodec<dynamic>? creationParamsCodec,
+    VoidCallback? onFocus,
   }) async {
     assert(id != null);
     assert(viewType != null);
@@ -227,6 +230,9 @@ class PlatformViewsService {
       );
     }
     await SystemChannels.platform_views.invokeMethod<void>('create', args);
+    if (onFocus != null) {
+      _instance._focusCallbacks[id] = onFocus;
+    }
     return UiKitViewController._(id, layoutDirection);
   }
 }

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

@@ -562,6 +562,7 @@ class _UiKitViewState extends State<UiKitView> {
   UiKitViewController? _controller;
   TextDirection? _layoutDirection;
   bool _initialized = false;
+  late FocusNode _focusNode;
 
   static final Set<Factory<OneSequenceGestureRecognizer>> _emptyRecognizersSet =
     <Factory<OneSequenceGestureRecognizer>>{};
@@ -571,10 +572,14 @@ class _UiKitViewState extends State<UiKitView> {
     if (_controller == null) {
       return const SizedBox.expand();
     }
-    return _UiKitPlatformView(
-      controller: _controller!,
-      hitTestBehavior: widget.hitTestBehavior,
-      gestureRecognizers: widget.gestureRecognizers ?? _emptyRecognizersSet,
+    return Focus(
+      focusNode: _focusNode,
+      onFocusChange: _onFocusChange,
+      child: _UiKitPlatformView(
+        controller: _controller!,
+        hitTestBehavior: widget.hitTestBehavior,
+        gestureRecognizers: widget.gestureRecognizers ?? _emptyRecognizersSet,
+      ),
     );
   }
 
@@ -639,13 +644,23 @@ class _UiKitViewState extends State<UiKitView> {
       layoutDirection: _layoutDirection!,
       creationParams: widget.creationParams,
       creationParamsCodec: widget.creationParamsCodec,
+      onFocus: () {
+        _focusNode.requestFocus();
+      }
     );
     if (!mounted) {
       controller.dispose();
       return;
     }
     widget.onPlatformViewCreated?.call(id);
-    setState(() { _controller = controller; });
+    setState(() {
+      _controller = controller;
+      _focusNode = FocusNode(debugLabel: 'UiKitView(id: $id)');
+    });
+  }
+
+  void _onFocusChange(bool isFocused) {
+    // TODO(hellohuanlin): send 'TextInput.setPlatformViewClient' channel message to engine after the engine is updated to handle this message.
   }
 }
 

packages/flutter/test/services/fake_platform_views.dart

@@ -340,6 +340,13 @@ class FakeIosPlatformViewsController {
     _registeredViewTypes.add(viewType);
   }
 
+  void invokeViewFocused(int viewId) {
+    final MethodCodec codec = SystemChannels.platform_views.codec;
+    final ByteData data = codec.encodeMethodCall(MethodCall('viewFocused', viewId));
+    ServicesBinding.instance.defaultBinaryMessenger
+        .handlePlatformMessage(SystemChannels.platform_views.name, data, (ByteData? data) {});
+  }
+
   Future<dynamic> _onMethodCall(MethodCall call) {
     switch(call.method) {
       case 'create':

packages/flutter/test/widgets/platform_view_test.dart

@@ -1978,7 +1978,7 @@ void main() {
       },
     );
 
-    testWidgets('AndroidView rebuilt with same gestureRecognizers', (WidgetTester tester) async {
+    testWidgets('UiKitView rebuilt with same gestureRecognizers', (WidgetTester tester) async {
       final FakeIosPlatformViewsController viewsController = FakeIosPlatformViewsController();
       viewsController.registerViewType('webview');
 
@@ -2012,6 +2012,59 @@ void main() {
       expect(factoryInvocationCount, 1);
     });
 
+    testWidgets('UiKitView can take input focus', (WidgetTester tester) async {
+      final int currentViewId = platformViewsRegistry.getNextPlatformViewId();
+      final FakeIosPlatformViewsController viewsController = FakeIosPlatformViewsController();
+      viewsController.registerViewType('webview');
+
+      final GlobalKey containerKey = GlobalKey();
+      await tester.pumpWidget(
+        Center(
+          child: Column(
+            children: <Widget>[
+              const SizedBox(
+                width: 200.0,
+                height: 100.0,
+                child: UiKitView(viewType: 'webview', layoutDirection: TextDirection.ltr),
+              ),
+              Focus(
+                debugLabel: 'container',
+                child: Container(key: containerKey),
+              ),
+            ],
+          ),
+        ),
+      );
+
+      // First frame is before the platform view was created so the render object
+      // is not yet in the tree.
+      await tester.pump();
+
+      final Focus uiKitViewFocusWidget = tester.widget(
+        find.descendant(
+          of: find.byType(UiKitView),
+          matching: find.byType(Focus),
+        ),
+      );
+      final FocusNode uiKitViewFocusNode = uiKitViewFocusWidget.focusNode!;
+      final Element containerElement = tester.element(find.byKey(containerKey));
+      final FocusNode containerFocusNode = Focus.of(containerElement);
+
+      containerFocusNode.requestFocus();
+
+      await tester.pump();
+
+      expect(containerFocusNode.hasFocus, isTrue);
+      expect(uiKitViewFocusNode.hasFocus, isFalse);
+
+      viewsController.invokeViewFocused(currentViewId + 1);
+
+      await tester.pump();
+
+      expect(containerFocusNode.hasFocus, isFalse);
+      expect(uiKitViewFocusNode.hasFocus, isTrue);
+    });
+
     testWidgets('UiKitView has correct semantics', (WidgetTester tester) async {
       final SemanticsHandle handle = tester.ensureSemantics();
       final int currentViewId = platformViewsRegistry.getNextPlatformViewId();
@@ -2039,7 +2092,14 @@ void main() {
       // is not yet in the tree.
       await tester.pump();
 
-      final SemanticsNode semantics = tester.getSemantics(find.byType(UiKitView));
+      final SemanticsNode semantics = tester.getSemantics(
+        find.descendant(
+          of: find.byType(UiKitView),
+          matching: find.byWidgetPredicate(
+              (Widget widget) => widget.runtimeType.toString() == '_UiKitPlatformView',
+          ),
+        ),
+      );
 
       expect(semantics.platformViewId, currentViewId + 1);
       expect(semantics.rect, const Rect.fromLTWH(0, 0, 200, 100));