PrimaryScrollController attached to multiple scroll views in TabBarView's keep-alive tabs #81152
Description
Recently, scroll views will auto generate a scrollbar on desktop. (?) In TabBarView, if we set every tab(with scrollable child like listview) keep-alive, then the auto generated scrollbar controller will attached to every tab. Then it will raise ScrollController attached to multiple scroll views. if we drag scrollbar after switching tab once.
Steps to Reproduce:
Run example code on desktop(windows/macOS):
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key? key, required this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage>
with SingleTickerProviderStateMixin {
late TabController _tabController;
@override
void initState() {
super.initState();
_tabController = TabController(length: 2, vsync: this);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
bottom: TabBar(
tabs: [Tab(text: 'TAB A'), Tab(text: 'TAB B')],
controller: _tabController,
),
),
body: TabBarView(
controller: _tabController,
children: [
KeepAliveBuilder(builder: (ctx) => ChildPage(name: 'Tab A')),
KeepAliveBuilder(builder: (ctx) => ChildPage(name: 'Tab B')),
],
),
);
}
}
class ChildPage extends StatelessWidget {
final String name;
const ChildPage({Key? key, required this.name}) : super(key: key);
@override
Widget build(BuildContext context) {
return ListView(
children: List.generate(
20,
(index) => ListTile(
title: Text('$name: $index'),
),
),
);
}
}
class KeepAliveBuilder extends StatefulWidget {
final WidgetBuilder builder;
final bool wantKeepAlive;
const KeepAliveBuilder(
{Key? key, required this.builder, this.wantKeepAlive = true})
: super(key: key);
@override
_KeepAliveBuilderState createState() => _KeepAliveBuilderState(wantKeepAlive);
}
class _KeepAliveBuilderState extends State<KeepAliveBuilder>
with AutomaticKeepAliveClientMixin {
bool _wantKeepAlive;
_KeepAliveBuilderState(this._wantKeepAlive);
@override
Widget build(BuildContext context) {
super.build(context);
return widget.builder(context);
}
@override
bool get wantKeepAlive => _wantKeepAlive;
}Expected results:
Actual results:
Logs
error
======== Exception caught by gesture ===============================================================
The following assertion was thrown while handling a gesture:
ScrollController attached to multiple scroll views.
'package:flutter/src/widgets/scroll_controller.dart':
Failed assertion: line 109 pos 12: '_positions.length == 1'
Either the assertion indicates an error in the framework itself, or we should provide substantially more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
https://github.com/flutter/flutter/issues/new?template=2_bug.md
When the exception was thrown, this was the stack:
#2 ScrollController.position (package:flutter/src/widgets/scroll_controller.dart:109:12)
#3 RawScrollbarState.getScrollbarDirection (package:flutter/src/widgets/scrollbar.dart:1080:34)
#4 RawScrollbarState.handleThumbPressStart (package:flutter/src/widgets/scrollbar.dart:1103:29)
#5 _MaterialScrollbarState.handleThumbPressStart (package:flutter/src/material/scrollbar.dart:388:11)
#6 RawScrollbarState._gestures.<anonymous closure>.<anonymous closure> (package:flutter/src/widgets/scrollbar.dart:1239:74)
...
Handler: "onLongPressStart"
Recognizer: _ThumbPressGestureRecognizer#0c12c
debugOwner: _MaterialScrollbarState#6eb61(tickers: tracking 2 tickers)
state: possible
====================================================================================================
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