Trigger MouseRegion.toHover only on hover events (#47403)

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

@@ -289,7 +289,6 @@ class MouseTracker extends ChangeNotifier {
       return;
 
     final PointerEvent previousEvent = existingState?.latestEvent;
-    final Offset lastHoverPosition = previousEvent is! PointerHoverEvent ? null : previousEvent.position;
     _updateDevices(
       targetEvent: event,
       handleUpdatedDevice: (_MouseState mouseState, LinkedHashSet<MouseTrackerAnnotation> previousAnnotations) {
@@ -297,7 +296,7 @@ class MouseTracker extends ChangeNotifier {
         _dispatchDeviceCallbacks(
           lastAnnotations: previousAnnotations,
           nextAnnotations: mouseState.annotations,
-          lastHoverPosition: lastHoverPosition,
+          previousEvent: previousEvent,
           unhandledEvent: event,
           trackedAnnotations: _trackedAnnotations,
         );
@@ -328,13 +327,11 @@ class MouseTracker extends ChangeNotifier {
   void _updateAllDevices() {
     _updateDevices(
       handleUpdatedDevice: (_MouseState mouseState, LinkedHashSet<MouseTrackerAnnotation> previousAnnotations) {
-        final PointerEvent latestEvent = mouseState.latestEvent;
-        final Offset lastHoverPosition = latestEvent is PointerHoverEvent ? latestEvent.position : null;
         _dispatchDeviceCallbacks(
           lastAnnotations: previousAnnotations,
           nextAnnotations: mouseState.annotations,
-          lastHoverPosition: lastHoverPosition,
+          previousEvent: mouseState.latestEvent,
-          unhandledEvent: mouseState.latestEvent,
+          unhandledEvent: null,
           trackedAnnotations: _trackedAnnotations,
         );
       }
@@ -427,20 +424,22 @@ class MouseTracker extends ChangeNotifier {
   // Dispatch callbacks related to a device after all necessary information
   // has been collected.
   //
-  // The `lastHoverPosition` can be null, which means the last event is not a
+  // The `previousEvent` is the latest event before `unhandledEvent`. It might be
-  // hover. Other arguments must not be null.
+  // null, which means the update is triggered by a new event.
+  // The `unhandledEvent` can be null, which means the update is not triggered
+  // by an event.
   static void _dispatchDeviceCallbacks({
     @required LinkedHashSet<MouseTrackerAnnotation> lastAnnotations,
     @required LinkedHashSet<MouseTrackerAnnotation> nextAnnotations,
-    @required Offset lastHoverPosition,
+    @required PointerEvent previousEvent,
     @required PointerEvent unhandledEvent,
     @required Set<MouseTrackerAnnotation> trackedAnnotations,
   }) {
     assert(lastAnnotations != null);
     assert(nextAnnotations != null);
-    // lastHoverPosition can be null
-    assert(unhandledEvent != null);
     assert(trackedAnnotations != null);
+    final PointerEvent latestEvent = unhandledEvent ?? previousEvent;
+    assert(latestEvent != null);
     // Order is important for mouse event callbacks. The `findAnnotations`
     // returns annotations in the visual order from front to back. We call
     // it the "visual order", and the opposite one "reverse visual order".
@@ -456,7 +455,7 @@ class MouseTracker extends ChangeNotifier {
       // trigger may cause exceptions and has safer alternatives. See
       // [MouseRegion.onExit] for details.
       if (annotation.onExit != null && attached) {
-        annotation.onExit(PointerExitEvent.fromMouseEvent(unhandledEvent));
+        annotation.onExit(PointerExitEvent.fromMouseEvent(latestEvent));
       }
     }
 
@@ -466,7 +465,7 @@ class MouseTracker extends ChangeNotifier {
     for (final MouseTrackerAnnotation annotation in enteringAnnotations) {
       assert(trackedAnnotations.contains(annotation));
       if (annotation.onEnter != null) {
-        annotation.onEnter(PointerEnterEvent.fromMouseEvent(unhandledEvent));
+        annotation.onEnter(PointerEnterEvent.fromMouseEvent(latestEvent));
       }
     }
 
@@ -476,6 +475,7 @@ class MouseTracker extends ChangeNotifier {
     if (unhandledEvent is PointerHoverEvent) {
       final Iterable<MouseTrackerAnnotation> hoveringAnnotations =
         nextAnnotations.toList().reversed;
+      final Offset lastHoverPosition = previousEvent is PointerHoverEvent ? previousEvent.position : null;
       for (final MouseTrackerAnnotation annotation in hoveringAnnotations) {
         // Deduplicate: Trigger hover if it's a newly hovered annotation
         // or the position has changed

packages/flutter/test/widgets/listener_deprecated_test.dart

@@ -107,8 +107,8 @@ void main() {
       final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
       await gesture.addPointer(location: Offset.zero);
       addTearDown(gesture.removePointer);
-      await gesture.moveTo(const Offset(400.0, 300.0));
       await tester.pump();
+      await gesture.moveTo(const Offset(400.0, 300.0));
       expect(move, isNotNull);
       expect(move.position, equals(const Offset(400.0, 300.0)));
       expect(enter, isNotNull);
@@ -593,8 +593,8 @@ void main() {
       TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
       await gesture.addPointer(location: Offset.zero);
       addTearDown(() => gesture?.removePointer());
-      await gesture.moveTo(tester.getCenter(find.byType(Container)));
       await tester.pumpAndSettle();
+      await gesture.moveTo(tester.getCenter(find.byType(Container)));
 
       expect(enter.length, 1);
       expect(enter.single.position, const Offset(400.0, 300.0));

packages/flutter/test/widgets/mouse_region_test.dart

@@ -101,8 +101,11 @@ void main() {
     final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     await gesture.addPointer(location: Offset.zero);
     addTearDown(gesture.removePointer);
-    await gesture.moveTo(const Offset(400.0, 300.0));
     await tester.pump();
+    move = null;
+    enter = null;
+    exit = null;
+    await gesture.moveTo(const Offset(400.0, 300.0));
     expect(move, isNotNull);
     expect(move.position, equals(const Offset(400.0, 300.0)));
     expect(enter, isNotNull);
@@ -132,15 +135,118 @@ void main() {
     await tester.pump();
     move = null;
     enter = null;
+    exit = null;
     await gesture.moveTo(const Offset(1.0, 1.0));
-    await tester.pump();
     expect(move, isNull);
     expect(enter, isNull);
     expect(exit, isNotNull);
     expect(exit.position, equals(const Offset(1.0, 1.0)));
   });
 
-  testWidgets('detects pointer exit when widget disappears', (WidgetTester tester) async {
+  testWidgets('triggers pointer enter when a mouse is connected', (WidgetTester tester) async {
+    PointerEnterEvent enter;
+    PointerHoverEvent move;
+    PointerExitEvent exit;
+    await tester.pumpWidget(Center(
+      child: MouseRegion(
+        child: Container(
+          width: 100.0,
+          height: 100.0,
+        ),
+        onEnter: (PointerEnterEvent details) => enter = details,
+        onHover: (PointerHoverEvent details) => move = details,
+        onExit: (PointerExitEvent details) => exit = details,
+      ),
+    ));
+    await tester.pump();
+
+    final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+    await gesture.addPointer(location: const Offset(400, 300));
+    addTearDown(gesture.removePointer);
+    expect(move, isNull);
+    expect(enter, isNull);
+    expect(exit, isNull);
+    await tester.pump();
+    expect(move, isNull);
+    expect(enter, isNotNull);
+    expect(enter.position, equals(const Offset(400.0, 300.0)));
+    expect(exit, isNull);
+  });
+
+  testWidgets('triggers pointer exit when a mouse is disconnected', (WidgetTester tester) async {
+    PointerEnterEvent enter;
+    PointerHoverEvent move;
+    PointerExitEvent exit;
+    await tester.pumpWidget(Center(
+      child: MouseRegion(
+        child: Container(
+          width: 100.0,
+          height: 100.0,
+        ),
+        onEnter: (PointerEnterEvent details) => enter = details,
+        onHover: (PointerHoverEvent details) => move = details,
+        onExit: (PointerExitEvent details) => exit = details,
+      ),
+    ));
+    await tester.pump();
+
+    TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+    await gesture.addPointer(location: const Offset(400, 300));
+    addTearDown(() => gesture?.removePointer);
+    await tester.pump();
+    move = null;
+    enter = null;
+    exit = null;
+    await gesture.removePointer();
+    gesture = null;
+    expect(move, isNull);
+    expect(enter, isNull);
+    expect(exit, isNotNull);
+    expect(exit.position, equals(const Offset(400.0, 300.0)));
+    exit = null;
+    await tester.pump();
+    expect(move, isNull);
+    expect(enter, isNull);
+    expect(exit, isNull);
+  });
+
+  testWidgets('triggers pointer enter when widget appears', (WidgetTester tester) async {
+    PointerEnterEvent enter;
+    PointerHoverEvent move;
+    PointerExitEvent exit;
+    await tester.pumpWidget(Center(
+      child: Container(
+        width: 100.0,
+        height: 100.0,
+      ),
+    ));
+    final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+    await gesture.addPointer(location: Offset.zero);
+    addTearDown(gesture.removePointer);
+    await gesture.moveTo(const Offset(400.0, 300.0));
+    await tester.pump();
+    expect(enter, isNull);
+    expect(move, isNull);
+    expect(exit, isNull);
+    await tester.pumpWidget(Center(
+      child: MouseRegion(
+        child: Container(
+          width: 100.0,
+          height: 100.0,
+        ),
+        onEnter: (PointerEnterEvent details) => enter = details,
+        onHover: (PointerHoverEvent details) => move = details,
+        onExit: (PointerExitEvent details) => exit = details,
+      ),
+    ));
+    await tester.pump();
+    expect(move, isNull);
+    expect(enter, isNotNull);
+    expect(enter.position, equals(const Offset(400.0, 300.0)));
+    expect(exit, isNull);
+  });
+
+  testWidgets("doesn't trigger pointer exit when widget disappears", (WidgetTester tester) async {
     PointerEnterEvent enter;
     PointerHoverEvent move;
     PointerExitEvent exit;
@@ -161,21 +267,105 @@ void main() {
     addTearDown(gesture.removePointer);
     await gesture.moveTo(const Offset(400.0, 300.0));
     await tester.pump();
-    expect(move, isNotNull);
+    move = null;
-    expect(move.position, equals(const Offset(400.0, 300.0)));
+    enter = null;
-    expect(enter, isNotNull);
+    exit = null;
-    expect(enter.position, equals(const Offset(400.0, 300.0)));
-    expect(exit, isNull);
     await tester.pumpWidget(Center(
       child: Container(
         width: 100.0,
         height: 100.0,
       ),
     ));
+    expect(enter, isNull);
+    expect(move, isNull);
     expect(exit, isNull);
     expect(tester.binding.mouseTracker.isAnnotationAttached(renderListener.hoverAnnotation), isFalse);
   });
 
+  testWidgets('triggers pointer enter when widget moves in', (WidgetTester tester) async {
+    PointerEnterEvent enter;
+    PointerHoverEvent move;
+    PointerExitEvent exit;
+    await tester.pumpWidget(Container(
+      alignment: Alignment.center,
+      child: MouseRegion(
+        child: Container(
+          width: 100.0,
+          height: 100.0,
+        ),
+        onEnter: (PointerEnterEvent details) => enter = details,
+        onHover: (PointerHoverEvent details) => move = details,
+        onExit: (PointerExitEvent details) => exit = details,
+      ),
+    ));
+    final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+    await gesture.addPointer(location: const Offset(1.0, 1.0));
+    addTearDown(gesture.removePointer);
+    await tester.pump();
+    expect(enter, isNull);
+    expect(move, isNull);
+    expect(exit, isNull);
+    await tester.pumpWidget(Container(
+      alignment: Alignment.topLeft,
+      child: MouseRegion(
+        child: Container(
+          width: 100.0,
+          height: 100.0,
+        ),
+        onEnter: (PointerEnterEvent details) => enter = details,
+        onHover: (PointerHoverEvent details) => move = details,
+        onExit: (PointerExitEvent details) => exit = details,
+      ),
+    ));
+    await tester.pump();
+    expect(enter, isNotNull);
+    expect(enter.position, equals(const Offset(1.0, 1.0)));
+    expect(move, isNull);
+    expect(exit, isNull);
+  });
+
+  testWidgets('triggers pointer exit when widget moves out', (WidgetTester tester) async {
+    PointerEnterEvent enter;
+    PointerHoverEvent move;
+    PointerExitEvent exit;
+    await tester.pumpWidget(Container(
+      alignment: Alignment.center,
+      child: MouseRegion(
+        child: Container(
+          width: 100.0,
+          height: 100.0,
+        ),
+        onEnter: (PointerEnterEvent details) => enter = details,
+        onHover: (PointerHoverEvent details) => move = details,
+        onExit: (PointerExitEvent details) => exit = details,
+      ),
+    ));
+    final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+    await gesture.addPointer(location: const Offset(400, 300));
+    addTearDown(gesture.removePointer);
+    await tester.pump();
+    enter = null;
+    move = null;
+    exit = null;
+    await tester.pumpWidget(Container(
+      alignment: Alignment.topLeft,
+      child: MouseRegion(
+        child: Container(
+          width: 100.0,
+          height: 100.0,
+        ),
+        onEnter: (PointerEnterEvent details) => enter = details,
+        onHover: (PointerHoverEvent details) => move = details,
+        onExit: (PointerExitEvent details) => exit = details,
+      ),
+    ));
+    await tester.pump();
+    expect(enter, isNull);
+    expect(move, isNull);
+    expect(exit, isNotNull);
+    expect(exit.position, equals(const Offset(400, 300)));
+  });
+
   testWidgets('Hover works with nested listeners', (WidgetTester tester) async {
     final UniqueKey key1 = UniqueKey();
     final UniqueKey key2 = UniqueKey();
@@ -680,8 +870,8 @@ void main() {
     TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     await gesture.addPointer(location: Offset.zero);
     addTearDown(() => gesture?.removePointer());
-    await gesture.moveTo(tester.getCenter(find.byType(Container)));
     await tester.pumpAndSettle();
+    await gesture.moveTo(tester.getCenter(find.byType(Container)));
 
     expect(enter.length, 1);
     expect(enter.single.position, const Offset(400.0, 300.0));