Scrollbar updates for native Android behavior (#76173)

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

@@ -69,6 +69,7 @@ class Scrollbar extends StatefulWidget {
     this.thickness,
     this.radius,
     this.notificationPredicate,
+    this.interactive,
   }) : super(key: key);
 
   /// {@macro flutter.widgets.Scrollbar.child}
@@ -111,6 +112,9 @@ class Scrollbar extends StatefulWidget {
   /// default [Radius.circular] of 8.0 pixels.
   final Radius? radius;
 
+  /// {@macro flutter.widgets.Scrollbar.interactive}
+  final bool? interactive;
+
   /// {@macro flutter.widgets.Scrollbar.notificationPredicate}
   final ScrollNotificationPredicate? notificationPredicate;
 
@@ -144,6 +148,7 @@ class _ScrollbarState extends State<Scrollbar> {
       thickness: widget.thickness,
       radius: widget.radius,
       notificationPredicate: widget.notificationPredicate,
+      interactive: widget.interactive,
     );
   }
 }
@@ -159,6 +164,7 @@ class _MaterialScrollbar extends RawScrollbar {
     double? thickness,
     Radius? radius,
     ScrollNotificationPredicate? notificationPredicate,
+    bool? interactive,
   }) : super(
          key: key,
          child: child,
@@ -170,6 +176,7 @@ class _MaterialScrollbar extends RawScrollbar {
          timeToFade: _kScrollbarTimeToFade,
          pressDuration: Duration.zero,
          notificationPredicate: notificationPredicate ?? defaultScrollNotificationPredicate,
+         interactive: interactive,
        );
 
   final bool? showTrackOnHover;
@@ -191,6 +198,9 @@ class _MaterialScrollbarState extends RawScrollbarState<_MaterialScrollbar> {
   @override
   bool get showScrollbar => widget.isAlwaysShown ?? _scrollbarTheme.isAlwaysShown ?? false;
 
+  @override
+  bool get enableGestures => widget.interactive ?? _scrollbarTheme.interactive ?? !_useAndroidScrollbar;
+
   bool get _showTrackOnHover => widget.showTrackOnHover ?? _scrollbarTheme.showTrackOnHover ?? false;
 
   Set<MaterialState> get _states => <MaterialState>{
@@ -208,12 +218,16 @@ class _MaterialScrollbarState extends RawScrollbarState<_MaterialScrollbar> {
       case Brightness.light:
         dragColor = onSurface.withOpacity(0.6);
         hoverColor = onSurface.withOpacity(0.5);
-        idleColor = onSurface.withOpacity(0.1);
+        idleColor = _useAndroidScrollbar
+          ? Theme.of(context).highlightColor.withOpacity(1.0)
+          : onSurface.withOpacity(0.1);
         break;
       case Brightness.dark:
         dragColor = onSurface.withOpacity(0.75);
         hoverColor = onSurface.withOpacity(0.65);
-        idleColor = onSurface.withOpacity(0.3);
+        idleColor = _useAndroidScrollbar
+          ? Theme.of(context).highlightColor.withOpacity(1.0)
+          : onSurface.withOpacity(0.3);
         break;
     }
 

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

@@ -41,6 +41,7 @@ class ScrollbarThemeData with Diagnosticable {
     this.crossAxisMargin,
     this.mainAxisMargin,
     this.minThumbLength,
+    this.interactive,
   });
 
   /// Overrides the default value of [Scrollbar.thickness] in all
@@ -58,6 +59,10 @@ class ScrollbarThemeData with Diagnosticable {
   /// descendant [Scrollbar] widgets.
   final bool? isAlwaysShown;
 
+  /// Overrides the default value of [Scrollbar.interactive] in all
+  /// descendant [Scrollbar] widgets.
+  final bool? interactive;
+
   /// Overrides the default value of [Scrollbar.radius] in all
   /// descendant widgets.
   final Radius? radius;
@@ -119,6 +124,7 @@ class ScrollbarThemeData with Diagnosticable {
     MaterialStateProperty<double?>? thickness,
     bool? showTrackOnHover,
     bool? isAlwaysShown,
+    bool? interactive,
     Radius? radius,
     MaterialStateProperty<Color?>? thumbColor,
     MaterialStateProperty<Color?>? trackColor,
@@ -131,6 +137,7 @@ class ScrollbarThemeData with Diagnosticable {
       thickness: thickness ?? this.thickness,
       showTrackOnHover: showTrackOnHover ?? this.showTrackOnHover,
       isAlwaysShown: isAlwaysShown ?? this.isAlwaysShown,
+      interactive: interactive ?? this.interactive,
       radius: radius ?? this.radius,
       thumbColor: thumbColor ?? this.thumbColor,
       trackColor: trackColor ?? this.trackColor,
@@ -152,6 +159,7 @@ class ScrollbarThemeData with Diagnosticable {
       thickness: _lerpProperties<double?>(a?.thickness, b?.thickness, t, lerpDouble),
       showTrackOnHover: t < 0.5 ? a?.showTrackOnHover : b?.showTrackOnHover,
       isAlwaysShown: t < 0.5 ? a?.isAlwaysShown : b?.isAlwaysShown,
+      interactive: t < 0.5 ? a?.interactive : b?.interactive,
       radius: Radius.lerp(a?.radius, b?.radius, t),
       thumbColor: _lerpProperties<Color?>(a?.thumbColor, b?.thumbColor, t, Color.lerp),
       trackColor: _lerpProperties<Color?>(a?.trackColor, b?.trackColor, t, Color.lerp),
@@ -168,6 +176,7 @@ class ScrollbarThemeData with Diagnosticable {
       thickness,
       showTrackOnHover,
       isAlwaysShown,
+      interactive,
       radius,
       thumbColor,
       trackColor,
@@ -188,6 +197,7 @@ class ScrollbarThemeData with Diagnosticable {
       && other.thickness == thickness
       && other.showTrackOnHover == showTrackOnHover
       && other.isAlwaysShown == isAlwaysShown
+      && other.interactive == interactive
       && other.radius == radius
       && other.thumbColor == thumbColor
       && other.trackColor == trackColor
@@ -203,6 +213,7 @@ class ScrollbarThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<MaterialStateProperty<double?>>('thickness', thickness, defaultValue: null));
     properties.add(DiagnosticsProperty<bool>('showTrackOnHover', showTrackOnHover, defaultValue: null));
     properties.add(DiagnosticsProperty<bool>('isAlwaysShown', isAlwaysShown, defaultValue: null));
+    properties.add(DiagnosticsProperty<bool>('interactive', interactive, defaultValue: null));
     properties.add(DiagnosticsProperty<Radius>('radius', radius, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('thumbColor', thumbColor, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('trackColor', trackColor, defaultValue: null));

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

@@ -612,6 +612,7 @@ class RawScrollbar extends StatefulWidget {
     this.timeToFade = _kScrollbarTimeToFade,
     this.pressDuration = Duration.zero,
     this.notificationPredicate = defaultScrollNotificationPredicate,
+    this.interactive,
   }) : assert(child != null),
        assert(fadeDuration != null),
        assert(timeToFade != null),
@@ -737,6 +738,11 @@ class RawScrollbar extends StatefulWidget {
   /// }
   /// ```
   /// {@end-tool}
+  ///
+  /// See also:
+  ///
+  ///   * [RawScrollbarState.showScrollbar], an overridable getter which uses
+  ///     this value to override the default behavior.
   /// {@endtemplate}
   final bool? isAlwaysShown;
 
@@ -782,6 +788,26 @@ class RawScrollbar extends StatefulWidget {
   /// {@endtemplate}
   final ScrollNotificationPredicate notificationPredicate;
 
+  /// {@template flutter.widgets.Scrollbar.interactive}
+  /// Whether the Scrollbar should be interactive and respond to dragging on the
+  /// thumb, or tapping in the track area.
+  ///
+  /// Does not apply to the [CupertinoScrollbar], which is always interactive to
+  /// match native behavior. On Android, the scrollbar is not interactive by
+  /// default.
+  ///
+  /// When false, the scrollbar will not respond to gesture or hover events.
+  ///
+  /// Defaults to true when null, unless on Android, which will default to false
+  /// when null.
+  ///
+  /// See also:
+  ///
+  ///   * [RawScrollbarState.enableGestures], an overridable getter which uses
+  ///     this value to override the default behavior.
+  /// {@endtemplate}
+  final bool? interactive;
+
   @override
   RawScrollbarState<RawScrollbar> createState() => RawScrollbarState<RawScrollbar>();
 }
@@ -815,9 +841,29 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   ///
   /// Subclasses can override this getter to make its value depend on an inherited
   /// theme.
+  ///
+  /// Defaults to false when [RawScrollbar.isAlwaysShown] is null.
+  ///
+  /// See also:
+  ///
+  ///   * [RawScrollbar.isAlwaysShown], which overrides the default behavior.
   @protected
   bool get showScrollbar => widget.isAlwaysShown ?? false;
 
+  /// Overridable getter to indicate is gestures should be enabled on the
+  /// scrollbar.
+  ///
+  /// Subclasses can override this getter to make its value depend on an inherited
+  /// theme.
+  ///
+  /// Defaults to true when [RawScrollbar.interactive] is null.
+  ///
+  /// See also:
+  ///
+  ///   * [RawScrollbar.interactive], which overrides the default behavior.
+  @protected
+  bool get enableGestures => widget.interactive ?? true;
+
   @override
   void initState() {
     super.initState();
@@ -1071,7 +1117,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
   Map<Type, GestureRecognizerFactory> get _gestures {
     final Map<Type, GestureRecognizerFactory> gestures = <Type, GestureRecognizerFactory>{};
     final ScrollController? controller = widget.controller ?? PrimaryScrollController.of(context);
-    if (controller == null)
+    if (controller == null || !enableGestures)
       return gestures;
 
     gestures[_ThumbPressGestureRecognizer] =
@@ -1190,7 +1236,8 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
             onExit: (PointerExitEvent event) {
               switch(event.kind) {
                 case PointerDeviceKind.mouse:
-                  handleHoverExit(event);
+                  if (enableGestures)
+                    handleHoverExit(event);
                   break;
                 case PointerDeviceKind.stylus:
                 case PointerDeviceKind.invertedStylus:
@@ -1202,7 +1249,8 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
             onHover: (PointerHoverEvent event) {
               switch(event.kind) {
                 case PointerDeviceKind.mouse:
-                  handleHover(event);
+                  if (enableGestures)
+                    handleHover(event);
                   break;
                 case PointerDeviceKind.stylus:
                 case PointerDeviceKind.invertedStylus:

packages/flutter/test/material/scrollbar_paint_test.dart

@@ -7,6 +7,8 @@ import 'package:flutter/material.dart';
 
 import '../rendering/mock_canvas.dart';
 
+const Color _kAndroidThumbIdleColor = Color(0xffbcbcbc);
+
 Widget _buildSingleChildScrollViewWithScrollbar({
   TextDirection textDirection = TextDirection.ltr,
   EdgeInsets padding = EdgeInsets.zero,
@@ -45,7 +47,7 @@ void main() {
         )
         ..rect(
           rect: const Rect.fromLTRB(796.0, 1.5, 800.0, 91.5),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
   });
@@ -72,7 +74,7 @@ void main() {
         )
         ..rect(
           rect: const Rect.fromLTRB(0.0, 1.5, 4.0, 91.5),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
   });
@@ -116,7 +118,7 @@ void main() {
         )
         ..rect(
           rect: const Rect.fromLTWH(796.0, 0.0, 4.0, (600.0 - 56 - 34 - 20) / 4000 * (600 - 56 - 34 - 20)),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
   });

packages/flutter/test/material/scrollbar_test.dart

@@ -14,6 +14,22 @@ import '../rendering/mock_canvas.dart';
 
 const Duration _kScrollbarFadeDuration = Duration(milliseconds: 300);
 const Duration _kScrollbarTimeToFade = Duration(milliseconds: 600);
+const Color _kAndroidThumbIdleColor = Color(0xffbcbcbc);
+const Rect _kAndroidTrackDimensions = Rect.fromLTRB(796.0, 0.0, 800.0, 600.0);
+const Radius _kDefaultThumbRadius = Radius.circular(8.0);
+const Color _kDefaultIdleThumbColor = Color(0x1a000000);
+const Offset _kTrackBorderPoint1 = Offset(796.0, 0.0);
+const Offset _kTrackBorderPoint2 = Offset(796.0, 600.0);
+
+Rect getStartingThumbRect({ required bool isAndroid }) {
+  return isAndroid
+    // On Android the thumb is slightly different. The thumb is only 4 pixels wide,
+    // and has no margin along the side of the viewport.
+    ? const Rect.fromLTRB(796.0, 0.0, 800.0, 90.0)
+    // The Material Design thumb is 8 pixels wide, with a 2
+    // pixel margin to the right edge of the viewport.
+    : const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0);
+}
 
 class TestCanvas implements Canvas {
   final List<Invocation> invocations = <Invocation>[];
@@ -509,17 +525,17 @@ void main() {
       paints
         ..rect(
           rect: const Rect.fromLTRB(780.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..line(
           p1: const Offset(780.0, 0.0),
           p2: const Offset(780.0, 600.0),
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
           rect: const Rect.fromLTRB(780.0, 0.0, 800.0, 300.0),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
     await tester.pumpWidget(viewWithScroll(radius: const Radius.circular(10)));
@@ -538,6 +554,7 @@ void main() {
         child: MediaQuery(
           data: const MediaQueryData(),
           child: Scrollbar(
+            interactive: true,
             isAlwaysShown: true,
             controller: scrollController,
             child: SingleChildScrollView(
@@ -555,18 +572,18 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
           rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 360.0),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
 
@@ -579,18 +596,18 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
           rect: const Rect.fromLTRB(796.0, 240.0, 800.0, 600.0),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
 
@@ -603,18 +620,18 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
           rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 360.0),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
   });
@@ -638,18 +655,18 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
           rect: const Rect.fromLTRB(796.0, 3.0, 800.0, 93.0),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
 
@@ -660,18 +677,18 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
           rect: const Rect.fromLTRB(796.0, 3.0, 800.0, 93.0),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
 
@@ -684,18 +701,18 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
           rect: const Rect.fromLTRB(796.0, 3.0, 800.0, 93.0),
-          color: const Color(0x14000000),
+          color: const Color(0xc6bcbcbc),
         ),
     );
   });
@@ -707,6 +724,7 @@ void main() {
         home: PrimaryScrollController(
           controller: scrollController,
           child: Scrollbar(
+            interactive: true,
             isAlwaysShown: true,
             controller: scrollController,
             child: const SingleChildScrollView(
@@ -722,18 +740,18 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 90.0),
-          color: const Color(0x1a000000),
+          rect: getStartingThumbRect(isAndroid: true),
+          color: _kAndroidThumbIdleColor,
         ),
     );
 
@@ -746,17 +764,17 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 90.0),
+          rect: getStartingThumbRect(isAndroid: true),
           // Drag color
           color: const Color(0x99000000),
         ),
@@ -774,18 +792,18 @@ void main() {
       find.byType(Scrollbar),
       paints
         ..rect(
-          rect: const Rect.fromLTRB(796.0, 0.0, 800.0, 600.0),
-          color: const Color(0x00000000),
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
         )
         ..line(
-          p1: const Offset(796.0, 0.0),
-          p2: const Offset(796.0, 600.0),
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
           strokeWidth: 1.0,
-          color: const Color(0x00000000),
+          color: Colors.transparent,
         )
         ..rect(
           rect: const Rect.fromLTRB(796.0, 10.0, 800.0, 100.0),
-          color: const Color(0x1a000000),
+          color: _kAndroidThumbIdleColor,
         ),
     );
   });
@@ -811,10 +829,10 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          getStartingThumbRect(isAndroid: false),
+          _kDefaultThumbRadius,
         ),
-        color: const Color(0x1a000000),
+        color: _kDefaultIdleThumbColor,
       ),
     );
 
@@ -828,8 +846,8 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          getStartingThumbRect(isAndroid: false),
+          _kDefaultThumbRadius,
         ),
         // Hover color
         color: const Color(0x80000000),
@@ -866,10 +884,10 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          getStartingThumbRect(isAndroid: false),
+          _kDefaultThumbRadius,
         ),
-        color: const Color(0x1a000000),
+        color: _kDefaultIdleThumbColor,
       ),
     );
     await tester.tapAt(const Offset(794.0, 5.0));
@@ -881,10 +899,10 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          getStartingThumbRect(isAndroid: false),
+          _kDefaultThumbRadius,
         ),
-        color: const Color(0x1a000000),
+        color: _kDefaultIdleThumbColor,
       ),
     );
 
@@ -906,13 +924,13 @@ void main() {
           p1: const Offset(784.0, 0.0),
           p2: const Offset(784.0, 600.0),
           strokeWidth: 1.0,
-          color: const Color(0x1a000000),
+          color: _kDefaultIdleThumbColor,
         )
         ..rrect(
           rrect: RRect.fromRectAndRadius(
             // Scrollbar thumb is larger
             const Rect.fromLTRB(786.0, 0.0, 798.0, 90.0),
-            const Radius.circular(8.0),
+            _kDefaultThumbRadius,
           ),
           // Hover color
           color: const Color(0x80000000),
@@ -947,10 +965,10 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          getStartingThumbRect(isAndroid: false),
+          _kDefaultThumbRadius,
         ),
-        color: const Color(0x1a000000),
+        color: _kDefaultIdleThumbColor,
       ),
     );
 
@@ -971,13 +989,13 @@ void main() {
           p1: const Offset(784.0, 0.0),
           p2: const Offset(784.0, 600.0),
           strokeWidth: 1.0,
-          color: const Color(0x1a000000),
+          color: _kDefaultIdleThumbColor,
         )
         ..rrect(
           rrect: RRect.fromRectAndRadius(
             // Scrollbar thumb is larger
             const Rect.fromLTRB(786.0, 0.0, 798.0, 90.0),
-            const Radius.circular(8.0),
+            _kDefaultThumbRadius,
           ),
           // Hover color
           color: const Color(0x80000000),
@@ -1121,4 +1139,140 @@ void main() {
       paintsExactlyCountTimes(#drawRect, 2),
     );
   }, variant: TargetPlatformVariant.all());
+
+  testWidgets('Scrollbar dragging can be disabled', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(
+      MaterialApp(
+        home: PrimaryScrollController(
+          controller: scrollController,
+          child: Scrollbar(
+            interactive: false,
+            isAlwaysShown: true,
+            controller: scrollController,
+            child: const SingleChildScrollView(
+              child: SizedBox(width: 4000.0, height: 4000.0),
+            ),
+          ),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(scrollController.offset, 0.0);
+    expect(
+      find.byType(Scrollbar),
+      paints
+        ..rect(
+          rect: const Rect.fromLTRB(788.0, 0.0, 800.0, 600.0),
+          color: Colors.transparent,
+        )
+        ..line(
+          p1: const Offset(788.0, 0.0),
+          p2: const Offset(788.0, 600.0),
+          strokeWidth: 1.0,
+          color: Colors.transparent,
+        )
+        ..rrect(
+          rrect: RRect.fromRectAndRadius(
+            getStartingThumbRect(isAndroid: false),
+            _kDefaultThumbRadius,
+          ),
+          color: _kDefaultIdleThumbColor,
+        ),
+    );
+
+    // 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();
+    await tester.pumpAndSettle();
+    // Dragging on the thumb does not change the offset.
+    expect(scrollController.offset, 0.0);
+
+    // 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();
+    await tester.pumpAndSettle();
+    // The scroll view received the drag.
+    expect(scrollController.offset, scrollAmount);
+
+    // Tap on the track to validate the scroll view will not page.
+    await tester.tapAt(const Offset(797.0, 200.0));
+    await tester.pumpAndSettle();
+    // The offset should not have changed.
+    expect(scrollController.offset, scrollAmount);
+  }, variant: const TargetPlatformVariant(<TargetPlatform>{
+    TargetPlatform.linux,
+    TargetPlatform.windows,
+    TargetPlatform.fuchsia,
+  }));
+
+  testWidgets('Scrollbar dragging is disabled by default on Android', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(
+      MaterialApp(
+        home: PrimaryScrollController(
+          controller: scrollController,
+          child: Scrollbar(
+            isAlwaysShown: true,
+            controller: scrollController,
+            child: const SingleChildScrollView(
+              child: SizedBox(width: 4000.0, height: 4000.0)
+            ),
+          ),
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    expect(scrollController.offset, 0.0);
+    expect(
+      find.byType(Scrollbar),
+      paints
+        ..rect(
+          rect: _kAndroidTrackDimensions,
+          color: Colors.transparent,
+        )
+        ..line(
+          p1: _kTrackBorderPoint1,
+          p2: _kTrackBorderPoint2,
+          strokeWidth: 1.0,
+          color: Colors.transparent,
+        )
+        ..rect(
+          rect: getStartingThumbRect(isAndroid: true),
+          color: _kAndroidThumbIdleColor,
+        ),
+    );
+
+    // 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();
+    await tester.pumpAndSettle();
+    // Dragging on the thumb does not change the offset.
+    expect(scrollController.offset, 0.0);
+
+    // 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();
+    await tester.pumpAndSettle();
+    // The scroll view received the drag.
+    expect(scrollController.offset, scrollAmount);
+
+    // Tap on the track to validate the scroll view will not page.
+    await tester.tapAt(const Offset(797.0, 200.0));
+    await tester.pumpAndSettle();
+    // The offset should not have changed.
+    expect(scrollController.offset, scrollAmount);
+  });
 }

packages/flutter/test/material/scrollbar_theme_test.dart

@@ -11,6 +11,14 @@ import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';
 
+// The const represents the the starting position of the scrollbar thumb for
+// the below tests. The thumb is 90 pixels long, and 8 pixels wide, with a 2
+// pixel margin to the right edge of the viewport.
+const Rect _kMaterialDesignInitialThumbRect = Rect.fromLTRB(790.0, 0.0, 798.0, 90.0);
+const Radius _kDefaultThumbRadius = Radius.circular(8.0);
+const Color _kDefaultIdleThumbColor = Color(0x1a000000);
+const Color _kDefaultDragThumbColor = Color(0x99000000);
+
 void main() {
   test('ScrollbarThemeData copyWith, ==, hashCode basics', () {
     expect(const ScrollbarThemeData(), const ScrollbarThemeData().copyWith());
@@ -38,10 +46,10 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          _kMaterialDesignInitialThumbRect,
+          _kDefaultThumbRadius,
         ),
-        color: const Color(0x1a000000),
+        color: _kDefaultIdleThumbColor,
       ),
     );
 
@@ -54,11 +62,11 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          _kMaterialDesignInitialThumbRect,
+          _kDefaultThumbRadius,
         ),
         // Drag color
-        color: const Color(0x99000000),
+        color: _kDefaultDragThumbColor,
       ),
     );
 
@@ -91,7 +99,7 @@ void main() {
           rrect: RRect.fromRectAndRadius(
             // Scrollbar thumb is larger
             const Rect.fromLTRB(786.0, 10.0, 798.0, 100.0),
-            const Radius.circular(8.0),
+            _kDefaultThumbRadius,
           ),
           // Hover color
           color: const Color(0x80000000),
@@ -192,6 +200,111 @@ void main() {
     }),
   );
 
+  testWidgets('ScrollbarTheme can disable gestures', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(scrollbarTheme: const ScrollbarThemeData(interactive: false)),
+      home: Scrollbar(
+        isAlwaysShown: true,
+        controller: scrollController,
+        child: SingleChildScrollView(
+          controller: scrollController,
+          child: const SizedBox(width: 4000.0, height: 4000.0)
+        ),
+      ),
+    ));
+    await tester.pumpAndSettle();
+    // Idle scrollbar behavior
+    expect(
+      find.byType(Scrollbar),
+      paints..rrect(
+        rrect: RRect.fromRectAndRadius(
+          _kMaterialDesignInitialThumbRect,
+          _kDefaultThumbRadius,
+        ),
+        color: _kDefaultIdleThumbColor,
+      ),
+    );
+
+    // Try to drag scrollbar.
+    const double scrollAmount = 10.0;
+    final TestGesture dragScrollbarGesture = await tester.startGesture(const Offset(797.0, 45.0));
+    await tester.pumpAndSettle();
+    await dragScrollbarGesture.moveBy(const Offset(0.0, scrollAmount));
+    await tester.pumpAndSettle();
+    await dragScrollbarGesture.up();
+    await tester.pumpAndSettle();
+    // Expect no change
+    expect(
+      find.byType(Scrollbar),
+      paints..rrect(
+        rrect: RRect.fromRectAndRadius(
+          _kMaterialDesignInitialThumbRect,
+          _kDefaultThumbRadius,
+        ),
+        color: _kDefaultIdleThumbColor,
+      ),
+    );
+  }, variant: const TargetPlatformVariant(<TargetPlatform>{
+    TargetPlatform.linux,
+    TargetPlatform.macOS,
+    TargetPlatform.windows,
+    TargetPlatform.fuchsia,
+  }));
+
+  testWidgets('Scrollbar.interactive takes priority over ScrollbarTheme', (WidgetTester tester) async {
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(scrollbarTheme: const ScrollbarThemeData(interactive: false)),
+      home: Scrollbar(
+        interactive: true,
+        isAlwaysShown: true,
+        controller: scrollController,
+        child: SingleChildScrollView(
+          controller: scrollController,
+          child: const SizedBox(width: 4000.0, height: 4000.0)
+        ),
+      ),
+    ));
+    await tester.pumpAndSettle();
+    // Idle scrollbar behavior
+    expect(
+      find.byType(Scrollbar),
+      paints..rrect(
+        rrect: RRect.fromRectAndRadius(
+          _kMaterialDesignInitialThumbRect,
+          _kDefaultThumbRadius,
+        ),
+        color: _kDefaultIdleThumbColor,
+      ),
+    );
+
+    // Drag scrollbar.
+    const double scrollAmount = 10.0;
+    final TestGesture dragScrollbarGesture = await tester.startGesture(const Offset(797.0, 45.0));
+    await tester.pumpAndSettle();
+    await dragScrollbarGesture.moveBy(const Offset(0.0, scrollAmount));
+    await tester.pumpAndSettle();
+    await dragScrollbarGesture.up();
+    await tester.pumpAndSettle();
+    // Gestures handled by Scrollbar.
+    expect(
+      find.byType(Scrollbar),
+      paints..rrect(
+        rrect: RRect.fromRectAndRadius(
+          const Rect.fromLTRB(790.0, 10.0, 798.0, 100.0),
+          _kDefaultThumbRadius,
+        ),
+        color: _kDefaultIdleThumbColor,
+      ),
+    );
+  }, variant: const TargetPlatformVariant(<TargetPlatform>{
+    TargetPlatform.linux,
+    TargetPlatform.macOS,
+    TargetPlatform.windows,
+    TargetPlatform.fuchsia,
+  }));
+
   testWidgets('Scrollbar widget properties take priority over theme', (WidgetTester tester) async {
     const double thickness = 4.0;
     const double hoverThickness = 4.0;
@@ -226,7 +339,7 @@ void main() {
           const Rect.fromLTRB(794.0, 0.0, 798.0, 90.0),
           const Radius.circular(3.0),
         ),
-        color: const Color(0x1a000000),
+        color: _kDefaultIdleThumbColor,
       ),
     );
 
@@ -243,7 +356,7 @@ void main() {
           const Radius.circular(3.0),
         ),
         // Drag color
-        color: const Color(0x99000000),
+        color: _kDefaultDragThumbColor,
       ),
     );
 
@@ -316,10 +429,10 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          _kMaterialDesignInitialThumbRect,
+          _kDefaultThumbRadius,
         ),
-        color: const Color(0x1a000000),
+        color: _kDefaultIdleThumbColor,
       ),
     );
 
@@ -332,11 +445,11 @@ void main() {
       find.byType(Scrollbar),
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
-          const Rect.fromLTRB(790.0, 0.0, 798.0, 90.0),
-          const Radius.circular(8.0),
+          _kMaterialDesignInitialThumbRect,
+          _kDefaultThumbRadius,
         ),
         // Drag color
-        color: const Color(0x99000000),
+        color: _kDefaultDragThumbColor,
       ),
     );
 
@@ -369,7 +482,7 @@ void main() {
           rrect: RRect.fromRectAndRadius(
             // Scrollbar thumb is larger
             const Rect.fromLTRB(786.0, 10.0, 798.0, 100.0),
-            const Radius.circular(8.0),
+            _kDefaultThumbRadius,
           ),
           // Hover color
           color: const Color(0x80000000),
@@ -389,7 +502,7 @@ void main() {
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
           const Rect.fromLTRB(790.0, 10.0, 798.0, 100.0),
-          const Radius.circular(8.0),
+          _kDefaultThumbRadius,
         ),
         color: const Color(0x4dffffff),
       ),
@@ -404,7 +517,7 @@ void main() {
       paints..rrect(
         rrect: RRect.fromRectAndRadius(
           const Rect.fromLTRB(790.0, 10.0, 798.0, 100.0),
-          const Radius.circular(8.0),
+          _kDefaultThumbRadius,
         ),
         // Drag color
         color: const Color(0xbfffffff),
@@ -437,7 +550,7 @@ void main() {
           rrect: RRect.fromRectAndRadius(
             // Scrollbar thumb is larger
             const Rect.fromLTRB(786.0, 20.0, 798.0, 110.0),
-            const Radius.circular(8.0),
+            _kDefaultThumbRadius,
           ),
           // Hover color
           color: const Color(0xa6ffffff),