Allow to click through scrollbar when gestures are disabled (#91532)

packages/flutter/lib/src/material/scrollbar.dart

@@ -348,7 +348,8 @@ class _MaterialScrollbarState extends RawScrollbarState<_MaterialScrollbar> {
       ..mainAxisMargin = _scrollbarTheme.mainAxisMargin ?? 0.0
       ..minLength = _scrollbarTheme.minThumbLength ?? _kScrollbarMinLength
       ..padding = MediaQuery.of(context).padding
-      ..scrollbarOrientation = widget.scrollbarOrientation;
+      ..scrollbarOrientation = widget.scrollbarOrientation
+      ..ignorePointer = !enableGestures;
   }
 
   @override

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

@@ -90,6 +90,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     double minLength = _kMinThumbExtent,
     double? minOverscrollLength,
     ScrollbarOrientation? scrollbarOrientation,
+    bool ignorePointer = false,
   }) : assert(color != null),
        assert(radius == null || shape == null),
        assert(thickness != null),
@@ -102,6 +103,9 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
        assert(minOverscrollLength == null || minOverscrollLength >= 0),
        assert(padding != null),
        assert(padding.isNonNegative),
+       assert(trackColor != null),
+       assert(trackBorderColor != null),
+       assert(ignorePointer != null),
        _color = color,
        _textDirection = textDirection,
        _thickness = thickness,
@@ -114,7 +118,8 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
        _trackColor = trackColor,
        _trackBorderColor = trackBorderColor,
        _scrollbarOrientation = scrollbarOrientation,
-       _minOverscrollLength = minOverscrollLength ?? minLength {
+       _minOverscrollLength = minOverscrollLength ?? minLength,
+       _ignorePointer = ignorePointer {
     fadeoutOpacityAnimation.addListener(notifyListeners);
   }
 
@@ -341,6 +346,17 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     notifyListeners();
   }
 
+  /// Whether the painter will be ignored during hit testing.
+  bool get ignorePointer => _ignorePointer;
+  bool _ignorePointer;
+  set ignorePointer(bool value) {
+    if (ignorePointer == value)
+      return;
+
+    _ignorePointer = value;
+    notifyListeners();
+  }
+
   void _debugAssertIsValidOrientation(ScrollbarOrientation orientation) {
     assert(
     (_isVertical && _isVerticalOrientation(orientation)) || (!_isVertical && !_isVerticalOrientation(orientation)),
@@ -623,6 +639,9 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
       // We have not computed the scrollbar position yet.
       return false;
     }
+    if (ignorePointer) {
+      return false;
+    }
 
     if (!_lastMetricsAreScrollable) {
       return false;
@@ -659,6 +678,9 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     if (_thumbRect == null) {
       return false;
     }
+    if (ignorePointer) {
+      return false;
+    }
     // The thumb is not able to be hit when transparent.
     if (fadeoutOpacityAnimation.value == 0.0) {
       return false;
@@ -688,6 +710,9 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     if (_thumbRect == null) {
       return null;
     }
+    if (ignorePointer) {
+      return false;
+    }
     // The thumb is not able to be hit when transparent.
     if (fadeoutOpacityAnimation.value == 0.0) {
       return false;
@@ -716,7 +741,8 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
         || padding != oldDelegate.padding
         || minLength != oldDelegate.minLength
         || minOverscrollLength != oldDelegate.minOverscrollLength
-        || scrollbarOrientation != oldDelegate.scrollbarOrientation;
+        || scrollbarOrientation != oldDelegate.scrollbarOrientation
+        || ignorePointer != oldDelegate.ignorePointer;
   }
 
   @override
@@ -1104,7 +1130,8 @@ class RawScrollbar extends StatefulWidget {
   /// match native behavior. On Android, the scrollbar is not interactive by
   /// default.
   ///
-  /// When false, the scrollbar will not respond to gesture or hover events.
+  /// When false, the scrollbar will not respond to gesture or hover events,
+  /// and will allow to click through it.
   ///
   /// Defaults to true when null, unless on Android, which will default to false
   /// when null.
@@ -1176,6 +1203,9 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   /// Overridable getter to indicate is gestures should be enabled on the
   /// scrollbar.
   ///
+  /// When false, the scrollbar will not respond to gesture or hover events,
+  /// and will allow to click through it.
+  ///
   /// Subclasses can override this getter to make its value depend on an inherited
   /// theme.
   ///
@@ -1200,14 +1230,15 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
     );
     scrollbarPainter = ScrollbarPainter(
       color: widget.thumbColor ?? const Color(0x66BCBCBC),
-      minLength: widget.minThumbLength,
-      minOverscrollLength: widget.minOverscrollLength ?? widget.minThumbLength,
-      thickness: widget.thickness ?? _kScrollbarThickness,
       fadeoutOpacityAnimation: _fadeoutOpacityAnimation,
+      thickness: widget.thickness ?? _kScrollbarThickness,
+      radius: widget.radius,
       scrollbarOrientation: widget.scrollbarOrientation,
       mainAxisMargin: widget.mainAxisMargin,
       shape: widget.shape,
-      crossAxisMargin: widget.crossAxisMargin
+      crossAxisMargin: widget.crossAxisMargin,
+      minLength: widget.minThumbLength,
+      minOverscrollLength: widget.minOverscrollLength ?? widget.minThumbLength,
     );
   }
 
@@ -1342,7 +1373,8 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
       ..shape = widget.shape
       ..crossAxisMargin = widget.crossAxisMargin
       ..minLength = widget.minThumbLength
-      ..minOverscrollLength = widget.minOverscrollLength ?? widget.minThumbLength;
+      ..minOverscrollLength = widget.minOverscrollLength ?? widget.minThumbLength
+      ..ignorePointer = !enableGestures;
   }
 
   @override

packages/flutter/test/material/scrollbar_test.dart

@@ -12,6 +12,7 @@ import 'dart:ui' as ui;
 
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
+import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -1213,6 +1214,7 @@ void main() {
   }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.fuchsia }));
 
   testWidgets('Scrollbar dragging is disabled by default on Android', (WidgetTester tester) async {
+    int tapCount = 0;
     final ScrollController scrollController = ScrollController();
     await tester.pumpWidget(
       MaterialApp(
@@ -1221,8 +1223,18 @@ void main() {
           child: Scrollbar(
             isAlwaysShown: true,
             controller: scrollController,
-            child: const SingleChildScrollView(
-              child: SizedBox(width: 4000.0, height: 4000.0),
+            child: SingleChildScrollView(
+              dragStartBehavior: DragStartBehavior.down,
+              child: GestureDetector(
+                behavior: HitTestBehavior.opaque,
+                onTap: () {
+                  tapCount += 1;
+                },
+                child: const SizedBox(
+                  width: 4000.0,
+                  height: 4000.0,
+                ),
+              ),
             ),
           ),
         ),
@@ -1250,30 +1262,49 @@ void main() {
     );
 
     // Try to drag the thumb down.
-    const double scrollAmount = 10.0;
-    final TestGesture dragScrollbarThumbGesture = await tester.startGesture(const Offset(797.0, 45.0));
-    await tester.pumpAndSettle();
-    await dragScrollbarThumbGesture.moveBy(const Offset(0.0, scrollAmount));
-    await tester.pumpAndSettle();
-    await dragScrollbarThumbGesture.up();
+    const double scrollAmount = 50.0;
+    await tester.dragFrom(
+      const Offset(797.0, 45.0),
+      const Offset(0.0, scrollAmount),
+      touchSlopY: 0.0,
+    );
     await tester.pumpAndSettle();
     // Dragging on the thumb does not change the offset.
     expect(scrollController.offset, 0.0);
+    expect(tapCount, 0);
 
-    // Drag in the track area to validate pass through to scrollable.
-    final TestGesture dragPassThroughTrack = await tester.startGesture(const Offset(797.0, 250.0));
-    await dragPassThroughTrack.moveBy(const Offset(0.0, -scrollAmount));
-    await tester.pumpAndSettle();
-    await dragPassThroughTrack.up();
+    // Try to drag up in the thumb area to validate pass through to scrollable.
+    await tester.dragFrom(
+      const Offset(797.0, 45.0),
+      const Offset(0.0, -scrollAmount),
+    );
     await tester.pumpAndSettle();
     // The scroll view received the drag.
     expect(scrollController.offset, scrollAmount);
+    expect(tapCount, 0);
 
-    // Tap on the track to validate the scroll view will not page.
-    await tester.tapAt(const Offset(797.0, 200.0));
+    // Drag in the track area to validate pass through to scrollable.
+    await tester.dragFrom(
+      const Offset(797.0, 45.0),
+      const Offset(0.0, -scrollAmount),
+      touchSlopY: 0.0,
+    );
+    await tester.pumpAndSettle();
+    // The scroll view received the drag.
+    expect(scrollController.offset, scrollAmount * 2);
+    expect(tapCount, 0);
+
+    // Tap on the thumb to validate the scroll view receives a click.
+    await tester.tapAt(const Offset(797.0, 45.0));
+    await tester.pumpAndSettle();
+    expect(tapCount, 1);
+
+    // Tap on the track to validate the scroll view will not page and receives a click.
+    await tester.tapAt(const Offset(797.0, 400.0));
     await tester.pumpAndSettle();
     // The offset should not have changed.
-    expect(scrollController.offset, scrollAmount);
+    expect(scrollController.offset, scrollAmount * 2);
+    expect(tapCount, 2);
   });
 
   testWidgets('Simultaneous dragging and pointer scrolling does not cause a crash', (WidgetTester tester) async {