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fix bug: the old position lost if widget unmounted from the tree. #176

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fix bug: the old position lost if widget unmounted from the tree. #176

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16 changes: 15 additions & 1 deletion packages/linked_scroll_controller/lib/linked_scroll_controller.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -144,13 +144,27 @@ class _LinkedScrollController extends ScrollController {
@override
_LinkedScrollPosition createScrollPosition(ScrollPhysics physics,
ScrollContext context, ScrollPosition oldPosition) {
return _LinkedScrollPosition(
final newPosition = _LinkedScrollPosition(
this,
physics: physics,
context: context,
initialPixels: initialScrollOffset,
oldPosition: oldPosition,
);

if (oldPosition == null && _controllers._attachedControllers.isNotEmpty) {
final position = _controllers._attachedControllers.first.position;
if (newPosition.minScrollExtent == null &&
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@fryette fryette Dec 1, 2020 •
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it's throwing an exception because minScrollExtent cannot be null, and if private _minScrollExtent null->exception throws

newPosition.maxScrollExtent == null &&
position.minScrollExtent != null &&
position.maxScrollExtent != null) {
newPosition.applyContentDimensions(
position.minScrollExtent, position.maxScrollExtent);
}
newPosition.forcePixels(position.pixels);
}

return newPosition;
}

@override
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122 changes: 122 additions & 0 deletions packages/linked_scroll_controller/test/linked_scroll_controller_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -282,6 +282,35 @@ void main() {
expect(state._letters.position.pixels, 50.0);
expect(state._numbers.position.pixels, 50.0);
});

testWidgets('check position after tile is remounted', (tester) async {
await tester.pumpWidget(RemountTest());

await tester.fling(
find.text('ListView-A 1'), const Offset(0.0, -1000.0), 1000.0);
await tester.pumpAndSettle();

// ListView-A has been unmounted.
await tester.fling(
find.text('ListView-D 1'), const Offset(-50.0, 0.0), 500.0);
await tester.pumpAndSettle();

// ListView-A will be mounted.
await tester.fling(
find.text('ListView-D 2'), const Offset(0.0, 1000.0), 1000.0);
await tester.pumpAndSettle();

final state = tester.state<_RemountTestState>(find.byType(RemountTest));
final offset = state._controllers.offset;

tester.allStates.where((state) {
return (state is ScrollableState) &&
(state.widget.axis == Axis.horizontal);
}).forEach((state) {
final pixels = (state as ScrollableState).position.pixels;
expect(pixels, equals(offset));
});
});
});
}

Expand Down Expand Up @@ -359,6 +388,99 @@ class TestState extends State<Test> {
}
}

class RemountTest extends StatefulWidget {
@override
_RemountTestState createState() => _RemountTestState();
}

class _RemountTestState extends State<RemountTest> {
LinkedScrollControllerGroup _controllers;

ScrollController _controllerA;
ScrollController _controllerB;
ScrollController _controllerC;
ScrollController _controllerD;

@override
void initState() {
super.initState();
_controllers = LinkedScrollControllerGroup();
_controllerA = _controllers.addAndGet();
_controllerB = _controllers.addAndGet();
_controllerC = _controllers.addAndGet();
_controllerD = _controllers.addAndGet();
}

@override
Widget build(BuildContext context) {
final height = 400.0;
return Directionality(
textDirection: TextDirection.ltr,
child: ListView(
scrollDirection: Axis.vertical,
children: [
SizedBox(
height: height,
child: ListView(
scrollDirection: Axis.horizontal,
controller: _controllerA,
children: [
Tile('ListView-A 1'),
Tile('ListView-A 2'),
Tile('ListView-A 3'),
Tile('ListView-A 4'),
Tile('ListView-A 5'),
],
),
),
SizedBox(
height: height,
child: ListView(
scrollDirection: Axis.horizontal,
controller: _controllerB,
children: [
Tile('ListView-B 1'),
Tile('ListView-B 2'),
Tile('ListView-B 3'),
Tile('ListView-B 4'),
Tile('ListView-B 5'),
],
),
),
SizedBox(
height: height,
child: ListView(
scrollDirection: Axis.horizontal,
controller: _controllerC,
children: [
Tile('ListView-C 1'),
Tile('ListView-C 2'),
Tile('ListView-C 3'),
Tile('ListView-C 4'),
Tile('ListView-C 5'),
],
),
),
SizedBox(
height: height,
child: ListView(
scrollDirection: Axis.horizontal,
controller: _controllerD,
children: [
Tile('ListView-D 1'),
Tile('ListView-D 2'),
Tile('ListView-D 3'),
Tile('ListView-D 4'),
Tile('ListView-D 5'),
],
),
),
],
),
);
}
}

class Tile extends StatelessWidget {
final String caption;

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