Fix SelectionArea scrolling conflicts (#151138)

Fixes #150897

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

@@ -535,30 +535,60 @@ class SelectableRegionState extends State<SelectableRegion> with TextSelectionDe
   }
 
   void _initMouseGestureRecognizer() {
-    switch (defaultTargetPlatform) {
+    _gestureRecognizers[TapAndPanGestureRecognizer] = GestureRecognizerFactoryWithHandlers<TapAndPanGestureRecognizer>(
-      case TargetPlatform.android:
+          () => TapAndPanGestureRecognizer(
-      case TargetPlatform.fuchsia:
+            debugOwner:this,
-      case TargetPlatform.iOS:
+            supportedDevices: <PointerDeviceKind>{ PointerDeviceKind.mouse },
-      case TargetPlatform.linux:
+          ),
-      case TargetPlatform.macOS:
+          (TapAndPanGestureRecognizer instance) {
-      case TargetPlatform.windows:
+        instance
-        _gestureRecognizers[TapAndPanGestureRecognizer] = GestureRecognizerFactoryWithHandlers<TapAndPanGestureRecognizer>(
+          ..onTapDown = _startNewMouseSelectionGesture
-              () => TapAndPanGestureRecognizer(debugOwner:this),
+          ..onTapUp = _handleMouseTapUp
-              (TapAndPanGestureRecognizer instance) {
+          ..onDragStart = _handleMouseDragStart
-            instance
+          ..onDragUpdate = _handleMouseDragUpdate
-              ..onTapDown = _startNewMouseSelectionGesture
+          ..onDragEnd = _handleMouseDragEnd
-              ..onTapUp = _handleMouseTapUp
+          ..onCancel = _clearSelection
-              ..onDragStart = _handleMouseDragStart
+          ..dragStartBehavior = DragStartBehavior.down;
-              ..onDragUpdate = _handleMouseDragUpdate
+      },
-              ..onDragEnd = _handleMouseDragEnd
+    );
-              ..onCancel = _clearSelection
-              ..dragStartBehavior = DragStartBehavior.down;
-          },
-        );
-    }
   }
 
   void _initTouchGestureRecognizer() {
+    // A [TapAndHorizontalDragGestureRecognizer] is used on non-precise pointer devices
+    // like PointerDeviceKind.touch so [SelectableRegion] gestures do not conflict with
+    // ancestor Scrollable gestures in common scenarios like a vertically scrolling list view.
+    _gestureRecognizers[TapAndHorizontalDragGestureRecognizer] = GestureRecognizerFactoryWithHandlers<TapAndHorizontalDragGestureRecognizer>(
+          () => TapAndHorizontalDragGestureRecognizer(
+            debugOwner:this,
+            supportedDevices: PointerDeviceKind.values.where((PointerDeviceKind device) {
+              return device != PointerDeviceKind.mouse;
+            }).toSet(),
+          ),
+          (TapAndHorizontalDragGestureRecognizer instance) {
+        instance
+          // iOS does not provide a device specific touch slop
+          // unlike Android (~8.0), so the touch slop for a [Scrollable]
+          // always default to kTouchSlop which is 18.0. When
+          // [SelectableRegion] is the child of a horizontal
+          // scrollable that means the [SelectableRegion] will
+          // always win the gesture arena when competing with
+          // the ancestor scrollable because they both have
+          // the same touch slop threshold and the child receives
+          // the [PointerEvent] first. To avoid this conflict
+          // and ensure a smooth scrolling experience, on
+          // iOS the [TapAndHorizontalDragGestureRecognizer]
+          // will wait for all other gestures to lose before
+          // declaring victory.
+          ..eagerVictoryOnDrag = defaultTargetPlatform != TargetPlatform.iOS
+          ..onTapDown = _startNewMouseSelectionGesture
+          ..onTapUp = _handleMouseTapUp
+          ..onDragStart = _handleMouseDragStart
+          ..onDragUpdate = _handleMouseDragUpdate
+          ..onDragEnd = _handleMouseDragEnd
+          ..onCancel = _clearSelection
+          ..dragStartBehavior = DragStartBehavior.down;
+      },
+    );
     _gestureRecognizers[LongPressGestureRecognizer] = GestureRecognizerFactoryWithHandlers<LongPressGestureRecognizer>(
           () => LongPressGestureRecognizer(debugOwner: this, supportedDevices: _kLongPressSelectionDevices),
           (LongPressGestureRecognizer instance) {

packages/flutter/test/widgets/selectable_region_test.dart

@@ -312,6 +312,144 @@ void main() {
       semantics.dispose();
     });
 
+    testWidgets('Horizontal PageView beats SelectionArea child touch drag gestures on iOS', (WidgetTester tester) async {
+      final PageController pageController = PageController();
+      const String testValue = 'abc def ghi jkl mno pqr stu vwx yz';
+      final FocusNode focusNode = FocusNode();
+      addTearDown(focusNode.dispose);
+      addTearDown(pageController.dispose);
+
+      await tester.pumpWidget(
+        MaterialApp(
+          home: PageView(
+            controller: pageController,
+            children: <Widget>[
+              Center(
+                child: SelectableRegion(
+                  focusNode: focusNode,
+                  selectionControls: materialTextSelectionControls,
+                  child: const Text(testValue),
+                ),
+              ),
+              const SizedBox(
+                height: 200.0,
+                child: Center(
+                  child: Text('Page 2'),
+                ),
+              ),
+            ],
+          ),
+        ),
+      );
+
+      final RenderParagraph paragraph = tester.renderObject<RenderParagraph>(find.descendant(of: find.text(testValue), matching: find.byType(RichText)));
+      final Offset gPos = textOffsetToPosition(paragraph, testValue.indexOf('g'));
+      final Offset pPos = textOffsetToPosition(paragraph, testValue.indexOf('p'));
+
+      // A double tap + drag should take precendence over parent drags.
+      final TestGesture gesture = await tester.startGesture(gPos);
+      addTearDown(gesture.removePointer);
+      await tester.pump();
+      await gesture.up();
+      await tester.pump();
+      await gesture.down(gPos);
+      await tester.pumpAndSettle();
+      await gesture.moveTo(pPos);
+      await tester.pump();
+      await gesture.up();
+      await tester.pumpAndSettle();
+      expect(paragraph.selections, isNotEmpty);
+      expect(paragraph.selections[0], TextSelection(baseOffset: testValue.indexOf('g'), extentOffset: testValue.indexOf('p') + 3));
+
+      expect(pageController.page, isNotNull);
+      expect(pageController.page, 0.0);
+      // A horizontal drag directly on the SelectableRegion should move the page
+      // view to the next page.
+      final Rect selectableTextRect = tester.getRect(find.byType(SelectableRegion));
+      await tester.dragFrom(selectableTextRect.centerRight - const Offset(0.1, 0.0), const Offset(-500.0, 0.0));
+      await tester.pumpAndSettle();
+      expect(pageController.page, isNotNull);
+      expect(pageController.page, 1.0);
+    },
+      variant: TargetPlatformVariant.only(TargetPlatform.iOS),
+      skip: kIsWeb, // https://github.com/flutter/flutter/issues/125582.
+    );
+
+    testWidgets('Vertical PageView beats SelectionArea child touch drag gestures', (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/150897.
+      final PageController pageController = PageController();
+      const String testValue = 'abc def ghi jkl mno pqr stu vwx yz';
+      final FocusNode focusNode = FocusNode();
+      addTearDown(focusNode.dispose);
+      addTearDown(pageController.dispose);
+
+      await tester.pumpWidget(
+        MaterialApp(
+          home: PageView(
+            scrollDirection: Axis.vertical,
+            controller: pageController,
+            children: <Widget>[
+              Center(
+                child: SelectableRegion(
+                  focusNode: focusNode,
+                  selectionControls: materialTextSelectionControls,
+                  child: const Text(testValue),
+                ),
+              ),
+              const SizedBox(
+                height: 200.0,
+                child: Center(
+                  child: Text('Page 2'),
+                ),
+              ),
+            ],
+          ),
+        ),
+      );
+
+      final RenderParagraph paragraph = tester.renderObject<RenderParagraph>(find.descendant(of: find.text(testValue), matching: find.byType(RichText)));
+      final Offset gPos = textOffsetToPosition(paragraph, testValue.indexOf('g'));
+      final Offset pPos = textOffsetToPosition(paragraph, testValue.indexOf('p'));
+
+      // A double tap + drag should take precendence over parent drags.
+      final TestGesture gesture = await tester.startGesture(gPos);
+      addTearDown(gesture.removePointer);
+      await tester.pump();
+      await gesture.up();
+      await tester.pump();
+      await gesture.down(gPos);
+      await tester.pumpAndSettle();
+      await gesture.moveTo(pPos);
+      await tester.pump();
+      await gesture.up();
+      await tester.pumpAndSettle();
+      expect(paragraph.selections, isNotEmpty);
+      expect(paragraph.selections[0], TextSelection(baseOffset: testValue.indexOf('g'), extentOffset: testValue.indexOf('p') + 3));
+
+      expect(pageController.page, isNotNull);
+      expect(pageController.page, 0.0);
+      // A vertical drag directly on the SelectableRegion should move the page
+      // view to the next page.
+      final Rect selectableTextRect = tester.getRect(find.byType(SelectableRegion));
+      // Simulate a pan by drag vertically first.
+      await gesture.down(selectableTextRect.center);
+      await tester.pump();
+      await gesture.moveTo(selectableTextRect.center + const Offset(0.0, -200.0));
+      // Introduce horizontal movement.
+      await gesture.moveTo(selectableTextRect.center + const Offset(5.0, -300.0));
+      await gesture.moveTo(selectableTextRect.center + const Offset(-10.0, -400.0));
+      // Continue dragging vertically.
+      await gesture.moveTo(selectableTextRect.center + const Offset(0.0, -500.0));
+      await tester.pump();
+      await gesture.up();
+      await tester.pumpAndSettle();
+      expect(pageController.page, isNotNull);
+      expect(pageController.page, 1.0);
+    },
+      variant: TargetPlatformVariant.mobile(),
+      skip: kIsWeb, // https://github.com/flutter/flutter/issues/125582.
+    );
+
     testWidgets('mouse single-click selection collapses the selection', (WidgetTester tester) async {
       final UniqueKey spy = UniqueKey();
       final FocusNode focusNode = FocusNode();