Fix scrollable `TabBar` jittering #150041

TahaTesser · 2024-06-11T13:57:11Z

fixes TabBar with isScrollable set to true is broken

This regressed due to a tiny mistake in #146293

Code sample

expand to view the code sample

import 'dart:ui';

import 'package:flutter/material.dart';

/// Flutter code sample for [TabBar].

void main() => runApp(const TabBarApp());

class TabBarApp extends StatelessWidget {
  const TabBarApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: TabBarExample(),
    );
  }
}

class TabBarExample extends StatelessWidget {
  const TabBarExample({super.key});

  @override
  Widget build(BuildContext context) {
    final List<Tab> tabs =
        List<Tab>.generate(20, (int index) => Tab(text: 'Tab $index'));

    return ScrollConfiguration(
      behavior: ScrollConfiguration.of(context)
          .copyWith(dragDevices: <PointerDeviceKind>{
        PointerDeviceKind.touch,
        PointerDeviceKind.mouse,
      }),
      child: DefaultTabController(
        length: tabs.length,
        child: Scaffold(
          appBar: AppBar(
            title: const Text('TabBar Sample'),
            bottom: TabBar(
              isScrollable: true,
              tabs: tabs,
              tabAlignment: TabAlignment.start,
            ),
          ),
          body: TabBarView(
            children: <Widget>[
              for (int i = 0; i < tabs.length; i++)
                Center(
                  child: Text('Page $i'),
                ),
            ],
          ),
        ),
      ),
    );
  }
}

Before

before.mov

After

after.mov

Pre-launch Checklist

I read the Contributor Guide and followed the process outlined there for submitting PRs.
I read the Tree Hygiene wiki page, which explains my responsibilities.
I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
I signed the CLA.
I listed at least one issue that this PR fixes in the description above.
I updated/added relevant documentation (doc comments with ///).
I added new tests to check the change I am making, or this PR is test-exempt.
I followed the breaking change policy and added Data Driven Fixes where supported.
All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

PerLycke · 2024-06-13T08:40:39Z

Even though this fix works to some extent, it doesn't fix "TabBar with isScrollable set to true is broken" as with the changes proposed in this PR the TabBar jumps after swiping to Tab 3 and back to Tab 2:

Screen.Recording.2024-06-13.at.10.27.41.mov

TahaTesser · 2024-06-13T08:42:23Z

@PerLycke
Thank you so much for testing the PR code. I'm out of office today, I'll address your issue first thing tomorrow.

TahaTesser · 2024-06-14T10:36:10Z

@PerLycke
I just updated the fix and added a new test for the jitter at the start of the scrollable TabBar.

Could you please try it and confirm it works as expected?

PerLycke · 2024-06-16T08:52:34Z

@TahaTesser I can confirm it now works as expected 👍

justinmc

Tricky, good catch. LGTM 👍

FYI @nate-thegrate

nate-thegrate · 2024-06-17T18:06:42Z

packages/flutter/lib/src/material/tabs.dart

-      < 0 => lerpDouble(middlePosition, leadingPosition, index - value)!,
-      _   => lerpDouble(middlePosition, trailingPosition, value - index)!,


Thanks for catching my mistake here!

(And thanks @justinmc for letting me know!)

nate-thegrate · 2024-06-17T18:10:06Z

packages/flutter/lib/src/material/tabs.dart

+    final double offset = switch ((value, index)) {
+      (_, _) when value == index - 1.0 =>  leadingPosition ?? middlePosition,
+      (_, _) when value == index + 1.0 =>  trailingPosition ?? middlePosition,
+      (_, _) when value == index =>  middlePosition,
+      (_, _) when value < index =>  leadingPosition == null ? middlePosition : lerpDouble(middlePosition, leadingPosition, index - value)!,
+      (_, _) =>  trailingPosition == null ? middlePosition : lerpDouble(middlePosition, trailingPosition, value - index)!,
    };


It feels a bit weird to pass a record into a switch expression and then not use it.

Suggested change

final double offset = switch ((value, index)) {

(_, _) when value == index - 1.0 => leadingPosition ?? middlePosition,

(_, _) when value == index + 1.0 => trailingPosition ?? middlePosition,

(_, _) when value == index => middlePosition,

(_, _) when value < index => leadingPosition == null ? middlePosition : lerpDouble(middlePosition, leadingPosition, index - value)!,

(_, _) => trailingPosition == null ? middlePosition : lerpDouble(middlePosition, trailingPosition, value - index)!,

};

final double offset = switch (value - index) {

-1.0 => leadingPosition ?? middlePosition,

1.0 => trailingPosition ?? middlePosition,

0 => middlePosition,

< 0 => leadingPosition == null ? middlePosition : lerpDouble(middlePosition, leadingPosition, index - value)!,

_ => trailingPosition == null ? middlePosition : lerpDouble(middlePosition, trailingPosition, value - index)!,

};

I believe the logic is identical, based on a local test run.

This is better, thanks!

nate-thegrate

I really appreciate the effort put into correcting a previous error I made.

If we want to just merge right away, that's good with me 👍

Manual roll requested by stuartmorgan@google.com flutter/flutter@ccf3abe...6c06abb 2024-06-18 magder@google.com Add test for engine artifact framework permissions (flutter/flutter#148786) 2024-06-18 32538273+ValentinVignal@users.noreply.github.com Add test for icon_button.3.dart (flutter/flutter#149988) 2024-06-18 engine-flutter-autoroll@skia.org Roll Flutter Engine from 78fdd06af541 to 74f42ca3544c (6 revisions) (flutter/flutter#150421) 2024-06-18 tessertaha@gmail.com Fix transparent `dividerColor` breaks `TabBar.tabAlignment` (flutter/flutter#150350) 2024-06-18 tessertaha@gmail.com Fix scrollable `TabBar` jittering (flutter/flutter#150041) 2024-06-18 98614782+auto-submit[bot]@users.noreply.github.com Reverts "Reland 3: [CupertinoActionSheet] Match colors to native (#150386)" (flutter/flutter#150413) 2024-06-18 jason-simmons@users.noreply.github.com Extend the Windows web_tool_tests_1_2 shard timeout to 45 minutes (flutter/flutter#150393) 2024-06-18 engine-flutter-autoroll@skia.org Roll Flutter Engine from 1c4e5e230ecb to 78fdd06af541 (3 revisions) (flutter/flutter#150403) 2024-06-18 engine-flutter-autoroll@skia.org Roll Flutter Engine from a4f266f7eb1a to 1c4e5e230ecb (8 revisions) (flutter/flutter#150399) 2024-06-18 parlough@gmail.com Rename doc file to use standard hyphens (flutter/flutter#150314) 2024-06-17 120297255+PurplePolyhedron@users.noreply.github.com Fix typo in `SliverLayoutDimensions.hashCode` where not all properties are used in the hash code. (flutter/flutter#150306) 2024-06-17 srawlins@google.com Fix doc comment references to 'this' (flutter/flutter#150379) 2024-06-17 Lexycon@users.noreply.github.com Add 'fail-fast' argument to flutter test (flutter/flutter#149587) 2024-06-17 dev@alestiago.com Update matchesGoldenFile documentation reference to goldenFileComparator (flutter/flutter#150343) 2024-06-17 dkwingsmt@users.noreply.github.com Reland 3: [CupertinoActionSheet] Match colors to native (flutter/flutter#150386) 2024-06-17 jhy03261997@gmail.com [a11y] Add semantics: button to bottom navigation bar items and dropdown menu items (flutter/flutter#149375) 2024-06-17 yinxulolol@gmail.com Reland "sliverGridDelegate mainAxisExtent add assert (#148470)" (flutter/flutter#149720) 2024-06-17 36861262+QuncCccccc@users.noreply.github.com `ScaffoldBackgroundColor` should default to `ColorScheme.surface` (flutter/flutter#149772) 2024-06-17 katelovett@google.com Reland TreeSliver (flutter/flutter#149839) 2024-06-17 dkwingsmt@users.noreply.github.com Reland: [CupertinoActionSheet] Add sliding tap gesture (flutter/flutter#150219) 2024-06-17 engine-flutter-autoroll@skia.org Roll Flutter Engine from 5989f0215fed to a4f266f7eb1a (1 revision) (flutter/flutter#150377) If this roll has caused a breakage, revert this CL and stop the roller using the controls here: https://autoroll.skia.org/r/flutter-packages Please CC rmistry@google.com,stuartmorgan@google.com on the revert to ensure that a human is aware of the problem. To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose To report a problem with the AutoRoller itself, please file a bug: https://issues.skia.org/issues/new?component=1389291&template=1850622 Documentation for the AutoRoller is here: https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

github-actions bot added framework flutter/packages/flutter repository. See also f: labels. f: material design flutter/packages/flutter/material repository. labels Jun 11, 2024

TahaTesser marked this pull request as ready for review June 11, 2024 14:15

TahaTesser requested review from Piinks and goderbauer June 11, 2024 14:15

TahaTesser marked this pull request as draft June 13, 2024 08:41

Fix scrollable TabBar jittering

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TahaTesser marked this pull request as ready for review June 14, 2024 11:30

TahaTesser changed the title ~~Fix scrollable TabBar jitters in the middle position~~ Fix scrollable TabBar jittering Jun 17, 2024

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auto-submit bot merged commit a9f554a into flutter:master Jun 18, 2024

TahaTesser deleted the fix_scrollable_tab_bar_jitter branch June 18, 2024 08:31

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Fix transparent dividerColor breaks TabBar.tabAlignment #150350

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Notable Mishaps #156720

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		< 0 => lerpDouble(middlePosition, leadingPosition, index - value)!,
		_ => lerpDouble(middlePosition, trailingPosition, value - index)!,

Fix scrollable TabBar jittering #150041

Fix scrollable TabBar jittering #150041

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TahaTesser commented Jun 11, 2024

Code sample

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Fix scrollable `TabBar` jittering #150041

Fix scrollable `TabBar` jittering #150041