extendBodyBehindAppBar breaks ScrollController attachment #116120
Labels
d: stackoverflow
Good question for Stack Overflow
f: material design
flutter/packages/flutter/material repository.
f: scrolling
Viewports, list views, slivers, etc.
found in release: 3.3
Found to occur in 3.3
found in release: 3.6
Found to occur in 3.6
framework
flutter/packages/flutter repository. See also f: labels.
has reproducible steps
The issue has been confirmed reproducible and is ready to work on
P3
Issues that are less important to the Flutter project
team-design
Owned by Design Languages team
triaged-design
Triaged by Design Languages team
Comments
|
Reproducible using the code sample in the gist shared above. Pasted below for convenience. sampleimport 'package:flutter/material.dart';
void main() => runApp(const MyApp());
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) => const MaterialApp(
home: TestScreen(),
);
}
class TestScreen extends StatefulWidget {
const TestScreen({super.key});
@override
State<TestScreen> createState() => _TestScreenState();
}
class _TestScreenState extends State<TestScreen> {
final controller = ScrollController();
@override
Widget build(BuildContext context) {
return Scaffold(
extendBodyBehindAppBar: true,
appBar: PreferredSize(
preferredSize: const Size.fromHeight(56),
child: AnimatedBuilder(
animation: controller,
builder: (_, __) => AppBar(
title: Text(controller.offset.toString()),
),
),
),
body: ListView.builder(
controller: controller,
itemBuilder: (context, index) => SizedBox(
height: 32,
child: Text(index.toString()),
),
),
);
}
}logsflutter doctor -v |
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|
It looks like the AppBar in the sample code is expecting the position to always be attached, this is not necessarily true. The scroll controller may not have the position attached by the time the AppBar tries to access it. When In general, if you are going to access the position on a scroll controller, it is good practice to check if ScrollController.hasClients first. _BodyBuilder in Scaffold is likely where to look. It adds a LayoutBuilder if |
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I wanted to animate app bar depending on scroll position (with an image behind it, that's the whole point of animation):
That's how it looks like currently (with the snippet below, but after rebuilding the widget tree with setState):
After adding
extendBodyBehindAppBar: trueto the code, on initial load (before hot reload) the screen looks like this (screenshot from my example below):Relevant snippet:
Stacktrace:
Basically adding
extendBodyBehindAppBar: truesomehow causes the ScrollController to not get attached.Reproducible example:
https://gist.github.com/eEQK/82c113b4c5471dd33961f8c07b750015
Reproducible example in dartpad:
https://dartpad.dev/?id=82c113b4c5471dd33961f8c07b750015
In order to reproduce, copy the code from the gist and run it in dartpad.dev or run it as an application
I can consistently reproduce it on:
The text was updated successfully, but these errors were encountered: