StretchingOverscrollIndicator with AlwaysScrollableScrollPhysics jumps when changing direction #116522
Description
I observed some weird behaviour with the StretchingOverscrollIndicator, which doesn't look right to me. When changing the scroll direction while scrolling, there is a sudden jump - most likely caused by the transform origin of the indicator changing from topCenter to bottomCenter.
I observed this problem only when the content of the Scrollable doesn't fill the Scrollable completely. This is very noticeable when using ListView.builder, or when explicitly setting AlwaysScrollableScrollPhysics on a SingleChildScrollView.
Steps to Reproduce
- Execute
flutter runon the code sample - Trigger the
StrechingOverscrollIndicatorby pulling your finger down a reasonable distance - Move finger slightly up
Expected results: I expect the overscroll indicator not to jump suddenly. I would have assumed, when moving the finger up again after moving the finger down, it should just do the same but in reverse.
Actual results: There is a sudden jump, which makes the first item in the list display partly outside the bounds of the Scrollable.
Screen.Recording.2022-12-05.at.15.42.34.mov
Code sample
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
// Need to set `useMaterial3` to true so we use the stretching overscroll
// indicator.
useMaterial3: true,
),
home: Scaffold(
appBar: AppBar(
title: const Text("StrechingOverscrollIndicator"),
),
body: ListView.builder(
physics: const AlwaysScrollableScrollPhysics(),
itemBuilder: (context, index) {
return Container(
height: 50,
color: index % 2 == 0
? const Color(0xFFEEEEEE)
: const Color(0xFFCCCCCC),
child: Text("Index $index"),
);
},
itemCount: 7,
),
),
);
}
}Logs
Analyzing strech_overscroll_always_scrollable_physics...
No issues found! (ran in 1.0s)
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