Add a FocusNode for AndroidView widgets. (#32773)

The PlatformViewsService listens for `viewFocused` calls on the
platform_views system channel and fires a callback that focuses the
focus node for the relevant AndroidView widget.

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

@@ -50,7 +50,36 @@ typedef PlatformViewCreatedCallback = void Function(int id);
 ///
 /// See also: [PlatformView].
 class PlatformViewsService {
-  PlatformViewsService._();
+  PlatformViewsService._() {
+    SystemChannels.platform_views.setMethodCallHandler(_onMethodCall);
+  }
+
+  static PlatformViewsService _serviceInstance;
+
+  static PlatformViewsService get _instance {
+    _serviceInstance ??= PlatformViewsService._();
+    return _serviceInstance;
+  }
+
+  Future<void> _onMethodCall(MethodCall call) {
+    switch(call.method) {
+      case 'viewFocused':
+        final int id = call.arguments;
+        if (_focusCallbacks.containsKey(id)) {
+          _focusCallbacks[id]();
+        }
+        break;
+      default:
+        throw UnimplementedError('${call.method} was invoked but isn\'t implemented by PlatformViewsService');
+    }
+    return null;
+  }
+
+  /// Maps platform view IDs to focus callbacks.
+  ///
+  /// The callbacks are invoked when the platform view asks to be focused.
+  final Map<int, VoidCallback> _focusCallbacks = <int, VoidCallback>{};
+
 
   /// Creates a controller for a new Android view.
   ///
@@ -68,6 +97,9 @@ class PlatformViewsService {
   /// platform side. It should match the codec passed to the constructor of [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html#PlatformViewFactory-io.flutter.plugin.common.MessageCodec-).
   /// This is typically one of: [StandardMessageCodec], [JSONMessageCodec], [StringCodec], or [BinaryCodec].
   ///
+  /// `onFocus` is a callback that will be invoked when the Android View asks to get the
+  /// input focus.
+  ///
   /// The Android view will only be created after [AndroidViewController.setSize] is called for the
   /// first time.
   ///
@@ -79,18 +111,21 @@ class PlatformViewsService {
     @required TextDirection layoutDirection,
     dynamic creationParams,
     MessageCodec<dynamic> creationParamsCodec,
+    VoidCallback onFocus,
   }) {
     assert(id != null);
     assert(viewType != null);
     assert(layoutDirection != null);
     assert(creationParams == null || creationParamsCodec != null);
-    return AndroidViewController._(
+    final AndroidViewController controller = AndroidViewController._(
       id,
       viewType,
       creationParams,
       creationParamsCodec,
       layoutDirection,
     );
+    _instance._focusCallbacks[id] = onFocus ?? () {};
+    return controller;
   }
 
   // TODO(amirh): reference the iOS plugin API for registering a UIView factory once it lands.

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

@@ -9,6 +9,8 @@ import 'package:flutter/services.dart';
 
 import 'basic.dart';
 import 'debug.dart';
+import 'focus_manager.dart';
+import 'focus_scope.dart';
 import 'framework.dart';
 
 /// Embeds an Android view in the Widget hierarchy.
@@ -295,16 +297,20 @@ class _AndroidViewState extends State<AndroidView> {
   AndroidViewController _controller;
   TextDirection _layoutDirection;
   bool _initialized = false;
+  FocusNode _focusNode;
 
   static final Set<Factory<OneSequenceGestureRecognizer>> _emptyRecognizersSet =
     <Factory<OneSequenceGestureRecognizer>>{};
 
   @override
   Widget build(BuildContext context) {
-    return _AndroidPlatformView(
+    return Focus(
+      focusNode: _focusNode,
+      child: _AndroidPlatformView(
         controller: _controller,
         hitTestBehavior: widget.hitTestBehavior,
         gestureRecognizers: widget.gestureRecognizers ?? _emptyRecognizersSet,
+      ),
     );
   }
 
@@ -314,6 +320,7 @@ class _AndroidViewState extends State<AndroidView> {
     }
     _initialized = true;
     _createNewAndroidView();
+    _focusNode = FocusNode(debugLabel: 'AndroidView(id: $_id)');
   }
 
   @override
@@ -369,6 +376,9 @@ class _AndroidViewState extends State<AndroidView> {
       layoutDirection: _layoutDirection,
       creationParams: widget.creationParams,
       creationParamsCodec: widget.creationParamsCodec,
+      onFocus: () {
+        _focusNode.requestFocus();
+      }
     );
     if (widget.onPlatformViewCreated != null) {
       _controller.addOnPlatformViewCreatedListener(widget.onPlatformViewCreated);

packages/flutter/test/services/fake_platform_views.dart

@@ -32,6 +32,12 @@ class FakeAndroidPlatformViewsController {
     _registeredViewTypes.add(viewType);
   }
 
+  void invokeViewFocused(int viewId) {
+    final MethodCodec codec = SystemChannels.platform_views.codec;
+    final ByteData data = codec.encodeMethodCall(MethodCall('viewFocused', viewId));
+    BinaryMessages.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

@@ -853,6 +853,58 @@ void main() {
 
       handle.dispose();
     });
+
+    testWidgets('AndroidView can take input focus', (WidgetTester tester) async {
+      final int currentViewId = platformViewsRegistry.getNextPlatformViewId();
+      final FakeAndroidPlatformViewsController viewsController = FakeAndroidPlatformViewsController();
+      viewsController.registerViewType('webview');
+
+      viewsController.createCompleter = Completer<void>();
+
+      final GlobalKey containerKey = GlobalKey();
+      await tester.pumpWidget(
+        Center(
+          child: Column(
+            children: <Widget>[
+              const SizedBox(
+                width: 200.0,
+                height: 100.0,
+                child: AndroidView(viewType: 'webview', layoutDirection: TextDirection.ltr),
+              ),
+              Focus(
+                debugLabel: 'container',
+                child: Container(key: containerKey),
+              ),
+            ],
+          ),
+        ),
+      );
+
+      final Focus androidViewFocusWidget =
+      tester.widget(
+          find.descendant(
+              of: find.byType(AndroidView),
+              matching: find.byType(Focus)
+          )
+      );
+      final Element containerElement = tester.element(find.byKey(containerKey));
+      final FocusNode androidViewFocusNode = androidViewFocusWidget.focusNode;
+      final FocusNode containerFocusNode = Focus.of(containerElement);
+
+      containerFocusNode.requestFocus();
+
+      await tester.pump();
+
+      expect(containerFocusNode.hasFocus, isTrue);
+      expect(androidViewFocusNode.hasFocus, isFalse);
+
+      viewsController.invokeViewFocused(currentViewId + 1);
+
+      await tester.pump();
+
+      expect(containerFocusNode.hasFocus, isFalse);
+      expect(androidViewFocusNode.hasFocus, isTrue);
+    });
   });
 
   group('UiKitView', () {