DraggableScrollableSheet.snap throws for multiple ScrollPositions attached #105469
Description
Internal bug: b/234838047
Steps to Reproduce
- Execute
flutter runon the code sample - Tap on button
Expected results:
The views animate from one to the other.
Actual results:
An assertion is thrown.
ScrollController attached to multiple scroll views.
This is because during the animation, the DraggableScrollableSheet tries to access the ScrollPosition through the ScrollController - but more than one position is attached. This appears to be caused by a post frame callback that is triggered by snap being true.
It may be that there is a condition we are not accounting for when initiating the snap.
Code sample
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return const MaterialApp(
home: MyHomePage(title: 'Draggable Bug'),
);
}
}
class View1 extends StatelessWidget {
View1({required this.next});
final void Function() next;
@override
Widget build(BuildContext context) {
return ListView(
children: [
ElevatedButton(
onPressed: next,
child: Text('switch to View2'),
),
Container(
height: 400,
color: Colors.blue,
),
],
);
}
}
class View2 extends StatelessWidget {
View2({required this.next});
final void Function() next;
@override
Widget build(BuildContext context) {
return ListView(
children: [
ElevatedButton(
onPressed: next,
child: Text('switch to View1'),
),
Container(
height: 400,
color: Colors.red,
),
],
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({super.key, required this.title});
final String title;
@override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
var s = 0;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: DraggableScrollableSheet(
initialChildSize: 0.25,
minChildSize: 0.25,
snap: true,
snapSizes: const [0.25, 0.5, 1.0],
builder: (context, scrollController) {
return PrimaryScrollController(
controller: scrollController,
child: AnimatedSwitcher(
duration: const Duration(milliseconds: 500),
child: (s % 2 == 0)
? View1(
next: () {
setState(() {
++s;
});
},
)
: View2(
next: () {
setState(() {
++s;
});
},
),
),
);
},
),
);
}
}
Logs
[✓] Flutter (Channel master, 3.1.0-0.0.pre.1119, on macOS 12.4 21F79 darwin-x64, locale en)
• Flutter version 3.1.0-0.0.pre.1119 at /Users/katelovett/_github/flutter
• Upstream repository [email protected]:flutter/flutter.git
• Framework revision 1b2ee411aa (6 hours ago), 2022-06-06 07:55:09 -0700
• Engine revision 4e42059e16
• Dart version 2.18.0 (build 2.18.0-170.0.dev)
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• Android SDK at /Users/katelovett/Library/Android/sdk
• Platform android-31, build-tools 31.0.0-rc2
• Java binary at: /Applications/Android Studio with
Blaze.app/Contents/jre/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7281165)
• All Android licenses accepted.
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• Xcode at /Applications/Xcode.app/Contents/Developer
• CocoaPods version 1.11.2
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• Android Studio at /Applications/Android Studio with Blaze Beta.app/Contents
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• Java version OpenJDK Runtime Environment (build 11.0.13+0-b1751.21-8125866)
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• IntelliJ at /Applications/IntelliJ UE (stable).app
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• VS Code at /Applications/Visual Studio Code.app/Contents
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[✓] Connected device (4 available)
• Piinks Pro (mobile) • 00008110-000444E03C2A801E • ios
• iOS 15.5 19F77
• iPhone SE (3rd generation) (mobile) • 4E826BB1-B283-403A-8E94-8574FD7DA7D2 • ios
• com.apple.CoreSimulator.SimRuntime.iOS-15-4 (simulator)
• macOS (desktop) • macos • darwin-x64
• macOS 12.4 21F79 darwin-x64
• Chrome (web) • chrome • web-javascript
• Google Chrome 102.0.5005.61
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• No issues found!
I am not sure what the expected behavior is here regarding snap in this case where more than one position is attached
- should all positions snap?
- should none?
- should we throw a more informative error message, and if so how should the user resolve this?
This snap logic was added in #90354 by @caseycrogers
@dnfield and @xu-baolin may also know what the expected behavior here is.