Add viewId to PointerEvents (#128287)

Follow-up to https://github.com/flutter/engine/pull/42493.

packages/flutter/lib/src/gestures/binding.dart

@@ -288,7 +288,7 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
     // We convert pointer data to logical pixels so that e.g. the touch slop can be
     // defined in a device-independent manner.
     try {
-      _pendingPointerEvents.addAll(PointerEventConverter.expand(packet.data, platformDispatcher.implicitView!.devicePixelRatio));
+      _pendingPointerEvents.addAll(PointerEventConverter.expand(packet.data, _devicePixelRatioForView));
       if (!locked) {
         _flushPointerEventQueue();
       }
@@ -302,6 +302,10 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
     }
   }
 
+  double? _devicePixelRatioForView(int viewId) {
+    return platformDispatcher.view(id: viewId)?.devicePixelRatio;
+  }
+
   /// Dispatch a [PointerCancelEvent] for the given pointer soon.
   ///
   /// The pointer event will be dispatched before the next pointer event and
@@ -368,7 +372,7 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
     if (event is PointerDownEvent || event is PointerSignalEvent || event is PointerHoverEvent || event is PointerPanZoomStartEvent) {
       assert(!_hitTests.containsKey(event.pointer), 'Pointer of ${event.toString(minLevel: DiagnosticLevel.debug)} unexpectedly has a HitTestResult associated with it.');
       hitTestResult = HitTestResult();
-      hitTest(hitTestResult, event.position);
+      hitTestInView(hitTestResult, event.position, event.viewId);
       if (event is PointerDownEvent || event is PointerPanZoomStartEvent) {
         _hitTests[event.pointer] = hitTestResult;
       }
@@ -401,12 +405,22 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
     }
   }
 
-  /// Determine which [HitTestTarget] objects are located at a given position.
+  /// Determine which [HitTestTarget] objects are located at a given position in
+  /// the specified view.
   @override // from HitTestable
-  void hitTest(HitTestResult result, Offset position) {
+  void hitTestInView(HitTestResult result, Offset position, int viewId) {
     result.add(HitTestEntry(this));
   }
 
+  @override // from HitTestable
+  @Deprecated(
+    'Use hitTestInView and specify the view to hit test. '
+    'This feature was deprecated after v3.11.0-20.0.pre.',
+  )
+  void hitTest(HitTestResult result, Offset position) {
+    hitTestInView(result, position, platformDispatcher.implicitView!.viewId);
+  }
+
   /// Dispatch an event to [pointerRouter] and the path of a hit test result.
   ///
   /// The `event` is routed to [pointerRouter]. If the `hitTestResult` is not

packages/flutter/lib/src/gestures/converter.dart

@@ -32,6 +32,18 @@ int _synthesiseDownButtons(int buttons, PointerDeviceKind kind) {
   }
 }
 
+/// Signature for a callback that returns the device pixel ratio of a
+/// [FlutterView] identified by the provided `viewId`.
+///
+/// Returns null if no view with the provided ID exists.
+///
+/// Used by [PointerEventConverter.expand].
+///
+/// See also:
+///
+///  * [FlutterView.devicePixelRatio] for an explanation of device pixel ratio.
+typedef DevicePixelRatioGetter = double? Function(int viewId);
+
 /// Converts from engine pointer data to framework pointer events.
 ///
 /// This takes [PointerDataPacket] objects, as received from the engine via
@@ -45,10 +57,15 @@ abstract final class PointerEventConverter {
   /// [dart:ui.FlutterView.devicePixelRatio]) is used to convert the incoming data
   /// from physical coordinates to logical pixels. See the discussion at
   /// [PointerEvent] for more details on the [PointerEvent] coordinate space.
-  static Iterable<PointerEvent> expand(Iterable<ui.PointerData> data, double devicePixelRatio) {
+  static Iterable<PointerEvent> expand(Iterable<ui.PointerData> data, DevicePixelRatioGetter devicePixelRatioForView) {
     return data
         .where((ui.PointerData datum) => datum.signalKind != ui.PointerSignalKind.unknown)
         .map<PointerEvent?>((ui.PointerData datum) {
+          final double? devicePixelRatio = devicePixelRatioForView(datum.viewId);
+          if (devicePixelRatio == null) {
+            // View doesn't exist anymore.
+            return null;
+          }
           final Offset position = Offset(datum.physicalX, datum.physicalY) / devicePixelRatio;
           final Offset delta = Offset(datum.physicalDeltaX, datum.physicalDeltaY) / devicePixelRatio;
           final double radiusMinor = _toLogicalPixels(datum.radiusMinor, devicePixelRatio);
@@ -62,6 +79,7 @@ abstract final class PointerEventConverter {
               switch (datum.change) {
                 case ui.PointerChange.add:
                   return PointerAddedEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     kind: kind,
                     device: datum.device,
@@ -79,6 +97,7 @@ abstract final class PointerEventConverter {
                   );
                 case ui.PointerChange.hover:
                   return PointerHoverEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     kind: kind,
                     device: datum.device,
@@ -102,6 +121,7 @@ abstract final class PointerEventConverter {
                   );
                 case ui.PointerChange.down:
                   return PointerDownEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     pointer: datum.pointerIdentifier,
                     kind: kind,
@@ -124,6 +144,7 @@ abstract final class PointerEventConverter {
                   );
                 case ui.PointerChange.move:
                   return PointerMoveEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     pointer: datum.pointerIdentifier,
                     kind: kind,
@@ -149,6 +170,7 @@ abstract final class PointerEventConverter {
                   );
                 case ui.PointerChange.up:
                   return PointerUpEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     pointer: datum.pointerIdentifier,
                     kind: kind,
@@ -172,6 +194,7 @@ abstract final class PointerEventConverter {
                   );
                 case ui.PointerChange.cancel:
                   return PointerCancelEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     pointer: datum.pointerIdentifier,
                     kind: kind,
@@ -194,6 +217,7 @@ abstract final class PointerEventConverter {
                   );
                 case ui.PointerChange.remove:
                   return PointerRemovedEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     kind: kind,
                     device: datum.device,
@@ -208,6 +232,7 @@ abstract final class PointerEventConverter {
                   );
                 case ui.PointerChange.panZoomStart:
                   return PointerPanZoomStartEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     pointer: datum.pointerIdentifier,
                     device: datum.device,
@@ -221,6 +246,7 @@ abstract final class PointerEventConverter {
                   final Offset panDelta =
                       Offset(datum.panDeltaX, datum.panDeltaY) / devicePixelRatio;
                   return PointerPanZoomUpdateEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     pointer: datum.pointerIdentifier,
                     device: datum.device,
@@ -234,6 +260,7 @@ abstract final class PointerEventConverter {
                   );
                 case ui.PointerChange.panZoomEnd:
                   return PointerPanZoomEndEvent(
+                    viewId: datum.viewId,
                     timeStamp: timeStamp,
                     pointer: datum.pointerIdentifier,
                     device: datum.device,
@@ -249,6 +276,7 @@ abstract final class PointerEventConverter {
               final Offset scrollDelta =
                   Offset(datum.scrollDeltaX, datum.scrollDeltaY) / devicePixelRatio;
               return PointerScrollEvent(
+                viewId: datum.viewId,
                 timeStamp: timeStamp,
                 kind: kind,
                 device: datum.device,
@@ -258,6 +286,7 @@ abstract final class PointerEventConverter {
               );
             case ui.PointerSignalKind.scrollInertiaCancel:
               return PointerScrollInertiaCancelEvent(
+                viewId: datum.viewId,
                 timeStamp: timeStamp,
                 kind: kind,
                 device: datum.device,
@@ -266,6 +295,7 @@ abstract final class PointerEventConverter {
               );
             case ui.PointerSignalKind.scale:
               return PointerScaleEvent(
+                viewId: datum.viewId,
                 timeStamp: timeStamp,
                 kind: kind,
                 device: datum.device,

packages/flutter/lib/src/gestures/hit_test.dart

@@ -16,11 +16,16 @@ export 'events.dart' show PointerEvent;
 
 /// An object that can hit-test pointers.
 abstract interface class HitTestable {
-  /// Check whether the given position hits this object.
-  ///
-  /// If this given position hits this object, consider adding a [HitTestEntry]
-  /// to the given hit test result.
+  /// Deprecated. Use [hitTestInView] instead.
+  @Deprecated(
+    'Use hitTestInView and specify the view to hit test. '
+    'This feature was deprecated after v3.11.0-20.0.pre.',
+  )
   void hitTest(HitTestResult result, Offset position);
+
+  /// Fills the provided [HitTestResult] with [HitTestEntry]s for objects that
+  /// are hit at the given `position` in the view identified by `viewId`.
+  void hitTestInView(HitTestResult result, Offset position, int viewId);
 }
 
 /// An object that can dispatch events.

packages/flutter/lib/src/gestures/resampler.dart

@@ -54,6 +54,7 @@ class PointerEventResampler {
     int buttons,
   ) {
     return PointerHoverEvent(
+      viewId: event.viewId,
       timeStamp: timeStamp,
       kind: event.kind,
       device: event.device,
@@ -86,6 +87,7 @@ class PointerEventResampler {
     int buttons,
   ) {
     return PointerMoveEvent(
+      viewId: event.viewId,
       timeStamp: timeStamp,
       pointer: pointerIdentifier,
       kind: event.kind,

packages/flutter/lib/src/rendering/binding.dart

@@ -519,9 +519,10 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
   }
 
   @override
-  void hitTest(HitTestResult result, Offset position) {
+  void hitTestInView(HitTestResult result, Offset position, int viewId) {
+    assert(viewId == renderView.flutterView.viewId);
     renderView.hitTest(result, position: position);
-    super.hitTest(result, position);
+    super.hitTestInView(result, position, viewId);
   }
 
   Future<void> _forceRepaint() {

packages/flutter/lib/src/rendering/view.dart

@@ -103,6 +103,8 @@ class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox>
     markNeedsLayout();
   }
 
+  /// The [FlutterView] into which this [RenderView] will render.
+  ui.FlutterView get flutterView => _view;
   final ui.FlutterView _view;
 
   /// Whether Flutter should automatically compute the desired system UI.

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

@@ -13,6 +13,7 @@ import 'debug.dart';
 import 'framework.dart';
 import 'media_query.dart';
 import 'overlay.dart';
+import 'view.dart';
 
 /// Signature for determining whether the given data will be accepted by a [DragTarget].
 ///
@@ -497,6 +498,7 @@ class _DraggableState<T extends Object> extends State<Draggable<T>> {
       feedbackOffset: widget.feedbackOffset,
       ignoringFeedbackSemantics: widget.ignoringFeedbackSemantics,
       ignoringFeedbackPointer: widget.ignoringFeedbackPointer,
+      viewId: View.of(context).viewId,
       onDragUpdate: (DragUpdateDetails details) {
         if (mounted && widget.onDragUpdate != null) {
           widget.onDragUpdate!(details);
@@ -756,6 +758,7 @@ class _DragAvatar<T extends Object> extends Drag {
     this.onDragEnd,
     required this.ignoringFeedbackSemantics,
     required this.ignoringFeedbackPointer,
+    required this.viewId,
   }) : _position = initialPosition {
     _entry = OverlayEntry(builder: _build);
     overlayState.insert(_entry!);
@@ -772,6 +775,7 @@ class _DragAvatar<T extends Object> extends Drag {
   final OverlayState overlayState;
   final bool ignoringFeedbackSemantics;
   final bool ignoringFeedbackPointer;
+  final int viewId;
 
   _DragTargetState<Object>? _activeTarget;
   final List<_DragTargetState<Object>> _enteredTargets = <_DragTargetState<Object>>[];
@@ -804,7 +808,7 @@ class _DragAvatar<T extends Object> extends Drag {
     _lastOffset = globalPosition - dragStartPoint;
     _entry!.markNeedsBuild();
     final HitTestResult result = HitTestResult();
-    WidgetsBinding.instance.hitTest(result, globalPosition + feedbackOffset);
+    WidgetsBinding.instance.hitTestInView(result, globalPosition + feedbackOffset, viewId);
 
     final List<_DragTargetState<Object>> targets = _getDragTargets(result.path).toList();
 

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

@@ -5018,7 +5018,7 @@ class _ScribbleFocusableState extends State<_ScribbleFocusable> implements Scrib
     }
     final Rect intersection = calculatedBounds.intersect(rect);
     final HitTestResult result = HitTestResult();
-    WidgetsBinding.instance.hitTest(result, intersection.center);
+    WidgetsBinding.instance.hitTestInView(result, intersection.center, View.of(context).viewId);
     return result.path.any((HitTestEntry entry) => entry.target == renderEditable);
   }
 

packages/flutter/test/gestures/gesture_binding_resample_event_on_widget_test.dart

@@ -39,42 +39,50 @@ void main() {
     final ui.PointerDataPacket packet = ui.PointerDataPacket(
       data: <ui.PointerData>[
         ui.PointerData(
-            change: ui.PointerChange.add,
-            timeStamp: epoch,
+          viewId: tester.view.viewId,
+          change: ui.PointerChange.add,
+          timeStamp: epoch,
         ),
         ui.PointerData(
-            change: ui.PointerChange.down,
-            timeStamp: epoch,
+          viewId: tester.view.viewId,
+          change: ui.PointerChange.down,
+          timeStamp: epoch,
         ),
         ui.PointerData(
-            change: ui.PointerChange.move,
-            physicalX: 15.0,
-            timeStamp: epoch + const Duration(milliseconds: 10),
+          viewId: tester.view.viewId,
+          change: ui.PointerChange.move,
+          physicalX: 15.0,
+          timeStamp: epoch + const Duration(milliseconds: 10),
         ),
         ui.PointerData(
-            change: ui.PointerChange.move,
-            physicalX: 30.0,
-            timeStamp: epoch + const Duration(milliseconds: 20),
+          viewId: tester.view.viewId,
+          change: ui.PointerChange.move,
+          physicalX: 30.0,
+          timeStamp: epoch + const Duration(milliseconds: 20),
         ),
         ui.PointerData(
-            change: ui.PointerChange.move,
-            physicalX: 45.0,
-            timeStamp: epoch + const Duration(milliseconds: 30),
+          viewId: tester.view.viewId,
+          change: ui.PointerChange.move,
+          physicalX: 45.0,
+          timeStamp: epoch + const Duration(milliseconds: 30),
         ),
         ui.PointerData(
-            change: ui.PointerChange.move,
-            physicalX: 50.0,
-            timeStamp: epoch + const Duration(milliseconds: 40),
+          viewId: tester.view.viewId,
+          change: ui.PointerChange.move,
+          physicalX: 50.0,
+          timeStamp: epoch + const Duration(milliseconds: 40),
         ),
         ui.PointerData(
-            change: ui.PointerChange.up,
-            physicalX: 60.0,
-            timeStamp: epoch + const Duration(milliseconds: 40),
+          viewId: tester.view.viewId,
+          change: ui.PointerChange.up,
+          physicalX: 60.0,
+          timeStamp: epoch + const Duration(milliseconds: 40),
         ),
         ui.PointerData(
-            change: ui.PointerChange.remove,
-            physicalX: 60.0,
-            timeStamp: epoch + const Duration(milliseconds: 40),
+          viewId: tester.view.viewId,
+          change: ui.PointerChange.remove,
+          physicalX: 60.0,
+          timeStamp: epoch + const Duration(milliseconds: 40),
         ),
       ],
     );

packages/flutter/test/gestures/gesture_binding_test.dart

@@ -175,7 +175,7 @@ void main() {
       ],
     );
 
-    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
 
     expect(events.length, 5);
     expect(events[0], isA<PointerAddedEvent>());
@@ -191,7 +191,7 @@ void main() {
         ui.PointerData(change: ui.PointerChange.add, device: 24),
       ],
     );
-    List<PointerEvent> events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+    List<PointerEvent> events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
 
     expect(events.length, 1);
     expect(events[0], isA<PointerAddedEvent>());
@@ -207,7 +207,7 @@ void main() {
         ui.PointerData(signalKind: ui.PointerSignalKind.scroll, device: 24, scrollDeltaY: double.negativeInfinity, scrollDeltaX: 10),
       ],
     );
-    events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+    events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
     expect(events.length, 0);
 
     // Send packet with a valid scroll event.
@@ -217,12 +217,12 @@ void main() {
       ],
     );
     // Make sure PointerEventConverter can expand when device pixel ratio is valid.
-    events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+    events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
     expect(events.length, 1);
     expect(events[0], isA<PointerScrollEvent>());
 
     // Make sure PointerEventConverter returns none when device pixel ratio is invalid.
-    events = PointerEventConverter.expand(packet.data, 0).toList();
+    events = PointerEventConverter.expand(packet.data, (int viewId) => 0).toList();
     expect(events.length, 0);
   });
 
@@ -234,7 +234,7 @@ void main() {
         ],
     );
 
-    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
 
     expect(events.length, 2);
     expect(events[0], isA<PointerAddedEvent>());
@@ -253,7 +253,7 @@ void main() {
       ],
     );
 
-    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
 
     expect(events.length, 5);
     expect(events[0], isA<PointerAddedEvent>());
@@ -280,7 +280,7 @@ void main() {
       ],
     );
 
-    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
 
     expect(events.length, 5);
     expect(events[0], isA<PointerAddedEvent>());
@@ -312,7 +312,7 @@ void main() {
         ],
       );
 
-      final List<PointerEvent> events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+      final List<PointerEvent> events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
 
       expect(events.length, 5);
       expect(events[0], isA<PointerAddedEvent>());
@@ -341,7 +341,7 @@ void main() {
       ],
     );
 
-    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+    final List<PointerEvent> events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
 
     expect(events.length, 5);
     expect(events[0], isA<PointerAddedEvent>());
@@ -371,7 +371,7 @@ void main() {
         ],
       );
 
-      final List<PointerEvent> events = PointerEventConverter.expand(packet.data, devicePixelRatio).toList();
+      final List<PointerEvent> events = PointerEventConverter.expand(packet.data, (int viewId) => devicePixelRatio).toList();
 
       expect(events.length, 5);
       expect(events[0], isA<PointerAddedEvent>());
@@ -429,4 +429,33 @@ void main() {
       FlutterError.onError = FlutterError.presentError;
     }
   });
+
+  test('PointerEventConverter processes view IDs', () {
+    const int startID = 987654;
+    const List<ui.PointerData> data = <ui.PointerData>[
+      ui.PointerData(viewId: startID + 0, change: ui.PointerChange.cancel), // ignore: avoid_redundant_argument_values
+      ui.PointerData(viewId: startID + 1, change: ui.PointerChange.add),
+      ui.PointerData(viewId: startID + 2, change: ui.PointerChange.remove),
+      ui.PointerData(viewId: startID + 3, change: ui.PointerChange.hover),
+      ui.PointerData(viewId: startID + 4, change: ui.PointerChange.down),
+      ui.PointerData(viewId: startID + 5, change: ui.PointerChange.move),
+      ui.PointerData(viewId: startID + 6, change: ui.PointerChange.up),
+      ui.PointerData(viewId: startID + 7, change: ui.PointerChange.panZoomStart),
+      ui.PointerData(viewId: startID + 8, change: ui.PointerChange.panZoomUpdate),
+      ui.PointerData(viewId: startID + 9, change: ui.PointerChange.panZoomEnd),
+    ];
+
+    final List<int> viewIds = <int>[];
+    double devicePixelRatioGetter(int viewId) {
+      viewIds.add(viewId);
+      return viewId / 10.0;
+    }
+
+    final List<PointerEvent> events = PointerEventConverter.expand(data, devicePixelRatioGetter).toList();
+
+    final List<int> expectedViewIds = List<int>.generate(10, (int index) => startID + index);
+    expect(viewIds, expectedViewIds);
+    expect(events, hasLength(10));
+    expect(events.map((PointerEvent event) => event.viewId), expectedViewIds);
+  });
 }

packages/flutter_test/lib/src/controller.dart

@@ -1192,7 +1192,8 @@ abstract class WidgetController {
   /// Forwards the given location to the binding's hitTest logic.
   HitTestResult hitTestOnBinding(Offset location) {
     final HitTestResult result = HitTestResult();
-    binding.hitTest(result, location);
+    // TODO(goderbauer): Support multiple views in flutter_test pointer event handling, https://github.com/flutter/flutter/issues/128281
+    binding.hitTest(result, location); // ignore: deprecated_member_use
     return result;
   }
 
@@ -1313,7 +1314,8 @@ abstract class WidgetController {
     final Offset location = box.localToGlobal(sizeToPoint(box.size));
     if (warnIfMissed) {
       final HitTestResult result = HitTestResult();
-      binding.hitTest(result, location);
+      // TODO(goderbauer): Support multiple views in flutter_test pointer event handling, https://github.com/flutter/flutter/issues/128281
+      binding.hitTest(result, location); // ignore: deprecated_member_use
       bool found = false;
       for (final HitTestEntry entry in result.path) {
         if (entry.target == box) {

packages/flutter_test/lib/src/finders.dart

@@ -642,7 +642,8 @@ class _HitTestableFinder extends ChainedFinder {
       final RenderBox box = candidate.renderObject! as RenderBox;
       final Offset absoluteOffset = box.localToGlobal(alignment.alongSize(box.size));
       final HitTestResult hitResult = HitTestResult();
-      WidgetsBinding.instance.hitTest(hitResult, absoluteOffset);
+      // TODO(goderbauer): Support multiple views in flutter_test pointer event handling, https://github.com/flutter/flutter/issues/128281
+      WidgetsBinding.instance.hitTest(hitResult, absoluteOffset); // ignore: deprecated_member_use
       for (final HitTestEntry entry in hitResult.path) {
         if (entry.target == candidate.renderObject) {
           yield candidate;

packages/flutter_test/lib/src/window.dart

@@ -167,8 +167,8 @@ class TestPlatformDispatcher implements PlatformDispatcher {
       : null;
   }
 
-  final Map<Object, TestFlutterView> _testViews = <Object, TestFlutterView>{};
-  final Map<Object, TestDisplay> _testDisplays = <Object, TestDisplay>{};
+  final Map<int, TestFlutterView> _testViews = <int, TestFlutterView>{};
+  final Map<int, TestDisplay> _testDisplays = <int, TestDisplay>{};
 
   @override
   VoidCallback? get onMetricsChanged => _platformDispatcher.onMetricsChanged;
@@ -510,6 +510,9 @@ class TestPlatformDispatcher implements PlatformDispatcher {
   @override
   Iterable<TestFlutterView> get views => _testViews.values;
 
+  @override
+  FlutterView? view({required int id}) => _testViews[id];
+
   @override
   Iterable<TestDisplay> get displays => _testDisplays.values;
 

packages/flutter_test/test/platform_dispatcher_test.dart

@@ -153,6 +153,10 @@ void main() {
     retrieveTestBinding(tester).platformDispatcher.localesTestValue = defaultLocales;
   });
 
+  testWidgets('TestPlatformDispatcher.view getter returns the implicit view', (WidgetTester tester) async {
+    expect(WidgetsBinding.instance.platformDispatcher.view(id: tester.view.viewId), same(tester.view));
+  });
+
   // TODO(pdblasi-google): Removed this group of tests when the Display API is stable and supported on all platforms.
   group('TestPlatformDispatcher with unsupported Display API', () {
     testWidgets('can initialize with empty displays', (WidgetTester tester) async {