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Improve Scrollbar drag behavior #112434

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Merged
merged 1 commit into from
Oct 24, 2022
Merged

Improve Scrollbar drag behavior #112434

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40 changes: 26 additions & 14 deletions packages/flutter/lib/src/widgets/scrollbar.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -686,6 +686,17 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
return scrollableExtent * thumbOffsetLocal / thumbMovableExtent;
}

/// The thumb's corresponding scroll offset in the track.
double getThumbScrollOffset() {
final double scrollableExtent = _lastMetrics!.maxScrollExtent - _lastMetrics!.minScrollExtent;

final double fractionPast = (scrollableExtent > 0)
? clampDouble(_lastMetrics!.pixels / scrollableExtent, 0.0, 1.0)
: 0;

return fractionPast * (_traversableTrackExtent - _thumbExtent);
}

// Converts between a scroll position and the corresponding position in the
// thumb track.
double _getScrollToTrack(ScrollMetrics metrics, double thumbExtent) {
Expand Down Expand Up @@ -1446,15 +1457,15 @@ class RawScrollbar extends StatefulWidget {
/// Provides defaults gestures for dragging the scrollbar thumb and tapping on the
/// scrollbar track.
class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProviderStateMixin<T> {
Offset? _dragScrollbarAxisOffset;
Offset? _startDragScrollbarAxisOffset;
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@TahaTesser Thanks for the sync info, I tested it and it did fix the issue by accident. : )

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@Piinks Hi, do you have a chance to take a look at this change? : )

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Ah yes, apologies! I was out of town and this got buried in my inbox. I checked it out before I left and forgot to click submit - sorry! 😓

double? _startDragThumbOffset;
ScrollController? _currentController;
Timer? _fadeoutTimer;
late AnimationController _fadeoutAnimationController;
late Animation<double> _fadeoutOpacityAnimation;
final GlobalKey _scrollbarPainterKey = GlobalKey();
bool _hoverIsActive = false;


/// Used to paint the scrollbar.
///
/// Can be customized by subclasses to change scrollbar behavior by overriding
Expand Down Expand Up @@ -1688,30 +1699,30 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv

void _updateScrollPosition(Offset updatedOffset) {
assert(_currentController != null);
assert(_dragScrollbarAxisOffset != null);
assert(_startDragScrollbarAxisOffset != null);
assert(_startDragThumbOffset != null);

final ScrollPosition position = _currentController!.position;
late double primaryDelta;
switch (position.axisDirection) {
case AxisDirection.up:
primaryDelta = _dragScrollbarAxisOffset!.dy - updatedOffset.dy;
primaryDelta = _startDragScrollbarAxisOffset!.dy - updatedOffset.dy;
break;
case AxisDirection.right:
primaryDelta = updatedOffset.dx -_dragScrollbarAxisOffset!.dx;
primaryDelta = updatedOffset.dx -_startDragScrollbarAxisOffset!.dx;
break;
case AxisDirection.down:
primaryDelta = updatedOffset.dy -_dragScrollbarAxisOffset!.dy;
primaryDelta = updatedOffset.dy -_startDragScrollbarAxisOffset!.dy;
break;
case AxisDirection.left:
primaryDelta = _dragScrollbarAxisOffset!.dx - updatedOffset.dx;
primaryDelta = _startDragScrollbarAxisOffset!.dx - updatedOffset.dx;
break;
}

// Convert primaryDelta, the amount that the scrollbar moved since the last
// time _updateScrollPosition was called, into the coordinate space of the scroll
// time when drag started, into the coordinate space of the scroll
// position, and jump to that position.
final double scrollOffsetLocal = scrollbarPainter.getTrackToScroll(primaryDelta);
final double scrollOffsetGlobal = scrollOffsetLocal + position.pixels;
final double scrollOffsetGlobal = scrollbarPainter.getTrackToScroll(primaryDelta + _startDragThumbOffset!);
if (scrollOffsetGlobal != position.pixels) {
// Ensure we don't drag into overscroll if the physics do not allow it.
final double physicsAdjustment = position.physics.applyBoundaryConditions(position, scrollOffsetGlobal);
Expand Down Expand Up @@ -1784,7 +1795,8 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
}
_fadeoutTimer?.cancel();
_fadeoutAnimationController.forward();
_dragScrollbarAxisOffset = localPosition;
_startDragScrollbarAxisOffset = localPosition;
_startDragThumbOffset = scrollbarPainter.getThumbScrollOffset();
}

/// Handler called when a currently active long press gesture moves.
Expand All @@ -1803,7 +1815,6 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
return;
}
_updateScrollPosition(localPosition);
_dragScrollbarAxisOffset = localPosition;
}

/// Handler called when a long press has ended.
Expand All @@ -1816,7 +1827,8 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
return;
}
_maybeStartFadeoutTimer();
_dragScrollbarAxisOffset = null;
_startDragScrollbarAxisOffset = null;
_startDragThumbOffset = null;
_currentController = null;
}

Expand Down Expand Up @@ -1958,7 +1970,7 @@ class RawScrollbarState<T extends RawScrollbar> extends State<T> with TickerProv
scrollbarPainter.update(metrics, metrics.axisDirection);
}
} else if (notification is ScrollEndNotification) {
if (_dragScrollbarAxisOffset == null) {
if (_startDragScrollbarAxisOffset == null) {
_maybeStartFadeoutTimer();
}
}
Expand Down
71 changes: 71 additions & 0 deletions packages/flutter/test/widgets/scrollbar_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -2717,4 +2717,75 @@ void main() {

expect(scrollController.offset, 0.0);
});

testWidgets('The thumb should follow the pointer when the scroll metrics changed during dragging', (WidgetTester tester) async {
// Regressing test for https://github.com/flutter/flutter/issues/112072
final ScrollController scrollController = ScrollController();
await tester.pumpWidget(
Directionality(
textDirection: TextDirection.ltr,
child: MediaQuery(
data: const MediaQueryData(),
child: PrimaryScrollController(
controller: scrollController,
child: RawScrollbar(
isAlwaysShown: true,
controller: scrollController,
child: CustomScrollView(
controller: scrollController,
// cacheExtent: double.maxFinite,
slivers: <Widget>[
SliverList(
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
final double height;
if (index < 10) {
height = 100;
} else {
height = 500;
}
return SizedBox(
height: height,
child: Text('$index'),
);
},
childCount: 100,
),
),
],
),
),
),
),
),
);
await tester.pumpAndSettle();
expect(scrollController.offset, 0.0);

// Drag the thumb down to scroll down.
const double scrollAmount = 100;
final TestGesture dragScrollbarGesture = await tester.startGesture(const Offset(797.0, 5.0));
await tester.pumpAndSettle();
await dragScrollbarGesture.moveBy(const Offset(0.0, scrollAmount));
await tester.pumpAndSettle();

await dragScrollbarGesture.moveBy(const Offset(0.0, scrollAmount));
await tester.pumpAndSettle();

await dragScrollbarGesture.up();
await tester.pumpAndSettle();

// The view has scrolled more than it would have by a swipe gesture of the
// same distance.
expect(scrollController.offset, greaterThan((100.0 * 10 + 500.0 * 90) / 3));
expect(
find.byType(RawScrollbar),
paints
..rect(rect: const Rect.fromLTRB(794.0, 0.0, 800.0, 600.0))
..rect(
rect: const Rect.fromLTRB(794.0, 200.0, 800.0, 218.0),
color: const Color(0x66BCBCBC),
),
);
});
}