AppBar shape disappears on AppBar elevation change when scrolling #145945

KristijanZic · 2024-03-29T00:12:29Z

Steps to reproduce

Following any setState (in app or via hot reloading) the AppBar shape will suddenly disappear when a SingleChildScrollView or a ListView in the same view moves from 0 or reaches 0. For the bug to happen again, setState has to be called again and the ScrollView/ListView has to move away from 0, if it was 0 initially, or reach 0 if it wasn't.

This bug only seems to be present in material 3, not material 2.

tested platforms: iOS, Android, Linux, macOS, web

affected platforms: iOS, Android, Linux, macOS, web
affected channels: stable, master
affected renderers: skia, impeller

Expected results

The AppBar shape should not ever disappear when set.

Actual results

AppBar shape clipper disappears when scrolling

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 MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
        shape: CustomAppBarShape(),
      ),

      body: SingleChildScrollView(
        primary: true,
        child: Column(
          children: [
            for (var i = 0; i < 100; i++)
              ListTile(
                title: Text('Test $i'),
                leading: Text('$_counter'),
              ),
          ],
        ),
      ),

      // The bug happens both with SingleChildScrollView and ListView scrolling
      // body: ListView(
      //   primary: true,
      //   children: [
      //     for (var i = 0; i < 1000; i++)
      //       ListTile(
      //         title: Text('Test $i'),
      //         leading: Text('$_counter'),
      //       ),
      //   ],
      // ),

      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

class CustomAppBarShape extends ContinuousRectangleBorder {
  @override
  Path getOuterPath(Rect rect, {TextDirection? textDirection}) {
    double height = rect.height + 80;
    double width = rect.width;

    print('SHAPE CALLED');

    var path = Path();
    path.lineTo(0, 0);
    path.lineTo(width, 0);
    path.lineTo(width, height + 40);
    path.lineTo(0, height - 100);
    path.close();
    return path;
  }
}

Screenshots or Video

Screenshots / Video demonstration

Simulator.Screen.Recording.-.iPhone.15.Pro.-.2024-03-29.at.00.43.49.mp4

Logs

[Paste your logs here]

Flutter Doctor output

Doctor output

[✓] Flutter (Channel master, 3.21.0-17.0.pre.19, on macOS 14.3.1 23D60 darwin-arm64, locale en-GB)
    • Flutter version 3.21.0-17.0.pre.19 on channel master at /Users/kristijanzic/Library/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 11d632e5dd (40 minutes ago), 2024-03-28 19:21:34 -0400
    • Engine revision b917b24836
    • Dart version 3.4.0 (build 3.4.0-282.0.dev)
    • DevTools version 2.34.1

[✓] Android toolchain - develop for Android devices (Android SDK version 33.0.1)
    • Android SDK at /Users/kristijanzic/Library/Android/sdk
    • Platform android-34, build-tools 33.0.1
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 15.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 15E204a
    • CocoaPods version 1.15.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2023.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)

[✓] IntelliJ IDEA Community Edition (version 2023.1)
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart

[✓] VS Code (version 1.87.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.84.0

[✓] Connected device (4 available)
    • iPhone 15 Pro (mobile)          • 6C492229-B053-4C1A-ADE2-785A83F06908 • ios            •
      com.apple.CoreSimulator.SimRuntime.iOS-17-4 (simulator)
    • macOS (desktop)                 • macos                                • darwin-arm64   • macOS 14.3.1 23D60
      darwin-arm64
    • Mac Designed for iPad (desktop) • mac-designed-for-ipad                • darwin         • macOS 14.3.1 23D60
      darwin-arm64
    • Chrome (web)                    • chrome                               • web-javascript • Google Chrome 122.0.6261.57

[✓] Network resources
    • All expected network resources are available.

• No issues found!

KristijanZic · 2024-03-29T04:44:31Z

I've dug some more into this and it seems that the flicker of the AppBar shape happens on AppBar elevation change when the content get's scrolled underneath the AppBar.

A workaround would be to set scrolledUnderElevation: 0.0, in the AppBar as that doesn't seem to call any state change and thus the shape doesn't flicker. Unfortunately that means that we won't be able to use the elevation feature as per Material 3 HIG.

huycozy · 2024-03-29T11:21:51Z

Thanks for the report. I'm able to reproduce the issue as well.

flutter doctor -v (stable and master)

[✓] Flutter (Channel stable, 3.19.5, on macOS 14.1 23B74 darwin-x64, locale en-VN)
    • Flutter version 3.19.5 on channel stable at /Users/huynq/Documents/GitHub/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 300451adae (25 hours ago), 2024-03-27 21:54:07 -0500
    • Engine revision e76c956498
    • Dart version 3.3.3
    • DevTools version 2.31.1

[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at /Users/huynq/Library/Android/sdk
    • Platform android-34, build-tools 34.0.0
    • ANDROID_HOME = /Users/huynq/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 15.2)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 15C500b
    • CocoaPods version 1.15.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2023.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • android-studio-dir = /Applications/Android Studio.app/
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)

[✓] VS Code (version 1.87.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.84.0

[✓] Connected device (3 available)
    • Pixel 7 (mobile) • 2B171FDH20084L • android-arm64  • Android 14 (API 34)
    • macOS (desktop)  • macos          • darwin-x64     • macOS 14.1 23B74 darwin-x64
    • Chrome (web)     • chrome         • web-javascript • Google Chrome 123.0.6312.86

[✓] Network resources
    • All expected network resources are available.

• No issues found!

[!] Flutter (Channel master, 3.21.0-17.0.pre.24, on macOS 14.1 23B74 darwin-x64, locale en-VN)
    • Flutter version 3.21.0-17.0.pre.24 on channel master at /Users/huynq/Documents/GitHub/flutter_master
    ! Warning: `flutter` on your path resolves to /Users/huynq/Documents/GitHub/flutter/bin/flutter, which is not inside your current Flutter SDK checkout at /Users/huynq/Documents/GitHub/flutter_master. Consider adding /Users/huynq/Documents/GitHub/flutter_master/bin to the front of your path.
    ! Warning: `dart` on your path resolves to /Users/huynq/Documents/GitHub/flutter/bin/dart, which is not inside your current Flutter SDK checkout at /Users/huynq/Documents/GitHub/flutter_master. Consider adding /Users/huynq/Documents/GitHub/flutter_master/bin to the front of your path.
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 1a2f34ab5b (63 minutes ago), 2024-03-28 19:39:17 -0700
    • Engine revision 68aa9ba386
    • Dart version 3.4.0 (build 3.4.0-282.0.dev)
    • DevTools version 2.34.1
    • If those were intentional, you can disregard the above warnings; however it is recommended to use "git" directly to perform update checks and upgrades.

[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at /Users/huynq/Library/Android/sdk
    • Platform android-34, build-tools 34.0.0
    • ANDROID_HOME = /Users/huynq/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 15.2)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 15C500b
    • CocoaPods version 1.15.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2023.2)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • android-studio-dir = /Applications/Android Studio.app/
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)

[✓] VS Code (version 1.87.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.84.0

[✓] Connected device (3 available)
    • Pixel 7 (mobile) • 2B171FDH20084L • android-arm64  • Android 14 (API 34)
    • macOS (desktop)  • macos          • darwin-x64     • macOS 14.1 23B74 darwin-x64
    • Chrome (web)     • chrome         • web-javascript • Google Chrome 123.0.6312.86

[✓] Network resources
    • All expected network resources are available.

! Doctor found issues in 1 category.

HansMuller · 2024-04-03T18:20:58Z

CC @Piinks

TahaTesser · 2024-04-05T12:56:01Z

Up on investigating this issue, this looks this is reproduced due to custom shape having incomplete implementation, without lerp functions or a const constructor.

This can be reproduced with just Material widget when updating elevation it rebuilds.

The custom shape without lerp functions fails to be identified by ShapeBorder.lerp as identical when the widget is rebuilt and falls back to parent shape which is ContinuousRectangleBorder in this case.

Complete custom shappe implementation should have lerp functions to identify the custom shape and lerp it's properties.

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

Line 847 in 45deb49

return ShapeBorder.lerp(begin, end, t);

expand to view the code sample

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  int _elevation = 0;

  void _incrementElevation() {
    setState(() {
      _elevation++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(useMaterial3: false),
      home: Scaffold(
        body: Center(
          child: GestureDetector(
            onTap: () {
              _incrementElevation();
            },
            child: Material(
              elevation: _elevation.toDouble(),
              color: Colors.red,
              shape: CustomShape(),
              child: const SizedBox(
                width: 100,
                height: 100,
                child: Center(child: Text('Tap me')),
              ),
            ),
          ),
        ),
      ),
    );
  }
}

class CustomShape extends ContinuousRectangleBorder {
  // const CustomShape();

  @override
  Path getOuterPath(Rect rect, {TextDirection? textDirection}) {
    double height = rect.height + 80;
    double width = rect.width;

    // print('SHAPE CALLED');

    var path = Path();
    path.lineTo(0, 0);
    path.lineTo(width, 0);
    path.lineTo(width, height + 40);
    path.lineTo(0, height - 100);
    path.close();
    return path;
  }

  //   @override
  // ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
  //   if (a is CustomShape) {
  //     return CustomShape();
  //   }
  //   return super.lerpFrom(a, t);
  // }

  // @override
  // ShapeBorder? lerpTo(ShapeBorder? b, double t) {
  //   if (b is CustomShape) {
  //     return CustomShape();
  //   }
  //   return super.lerpTo(b, t);
  // }
}

To fix this please implement lerp functions.

class CustomAppBarShape extends ContinuousRectangleBorder {
  const CustomAppBarShape({super.borderRadius = BorderRadius.zero});

  @override
  Path getOuterPath(Rect rect, {TextDirection? textDirection}) {
    double height = rect.height + 80;
    double width = rect.width;

    print('SHAPE CALLED');

    var path = Path();
    path.lineTo(0, 0);
    path.lineTo(width, 0);
    path.lineTo(width, height + 40);
    path.lineTo(0, height - 100);
    path.close();
    return path;
  }

  @override
  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
    if (a is CustomAppBarShape) {
      return CustomAppBarShape(borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t)!);
    }
    return super.lerpFrom(a, t);
  }

  @override
  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
    if (b is CustomAppBarShape) {
      return CustomAppBarShape(borderRadius: BorderRadiusGeometry.lerp(b.borderRadius, borderRadius, t)!);
    }
    return super.lerpTo(b, t);
  }
}

Fixed code sample for `AppBar`

expand to view the 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 MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
        shape: const CustomAppBarShape(),
      ),

      body: SingleChildScrollView(
        primary: true,
        child: Column(
          children: [
            for (var i = 0; i < 100; i++)
              ListTile(
                title: Text('Test $i'),
                leading: Text('$_counter'),
              ),
          ],
        ),
      ),

      // The bug happens both with SingleChildScrollView and ListView scrolling
      // body: ListView(
      //   primary: true,
      //   children: [
      //     for (var i = 0; i < 1000; i++)
      //       ListTile(
      //         title: Text('Test $i'),
      //         leading: Text('$_counter'),
      //       ),
      //   ],
      // ),

      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

class CustomAppBarShape extends ContinuousRectangleBorder {
  const CustomAppBarShape({super.borderRadius = BorderRadius.zero});

  @override
  Path getOuterPath(Rect rect, {TextDirection? textDirection}) {
    double height = rect.height + 80;
    double width = rect.width;

    print('SHAPE CALLED');

    var path = Path();
    path.lineTo(0, 0);
    path.lineTo(width, 0);
    path.lineTo(width, height + 40);
    path.lineTo(0, height - 100);
    path.close();
    return path;
  }

  @override
  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
    if (a is CustomAppBarShape) {
      return CustomAppBarShape(borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t)!);
    }
    return super.lerpFrom(a, t);
  }

  @override
  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
    if (b is CustomAppBarShape) {
      return CustomAppBarShape(borderRadius: BorderRadiusGeometry.lerp(b.borderRadius, borderRadius, t)!);
    }
    return super.lerpTo(b, t);
  }
}

Preview

This is similar to other shapes in the framework that do not reproduce this issue.

flutter/packages/flutter/lib/src/painting/stadium_border.dart

Lines 26 to 37 in 45deb49

    
           class StadiumBorder extends OutlinedBorder { 
        
             /// Create a stadium border. 
        
             const StadiumBorder({ super.side }); 
        
             @override 
        
             ShapeBorder scale(double t) => StadiumBorder(side: side.scale(t)); 
        
             @override 
        
             ShapeBorder? lerpFrom(ShapeBorder? a, double t) { 
        
               if (a is StadiumBorder) { 
        
                 return StadiumBorder(side: BorderSide.lerp(a.side, side, t)); 
        
               }

TahaTesser · 2024-04-05T13:01:10Z

@HansMuller
This seems to be working as expected.

Should we add an example for using custom shapes with Material or Material contained widgets such as AppBar?

HansMuller · 2024-04-05T16:09:11Z

I would never say no to adding an example. In this case I think it would be particularly worthwhile!

KristijanZic · 2024-04-06T11:15:28Z

I can confirm that this was in fact...a skill issue and it works perfectly fine with Taha's example. That said no linter has complained about the original example.

TahaTesser · 2024-04-08T12:45:08Z

That said no linter has complained about the original example.

These are optional methods. The constructor alone would've fixed the issue, as it allows identical method to properly compare custom shape objects. My new example include a comment for this and lerp functions, hopefully this will make it clear.

fixes [AppBar shape disappears on AppBar elevation change when scrolling](#145945) ### Description This PR adds an example for complete custom app bar for the `AppBar.shape` property. ### Preview ![Screenshot 2024-04-08 at 14 21 04](https://github.com/flutter/flutter/assets/48603081/ae3eda2b-b709-4652-9f2c-dd7b7dcfeb5c)

github-actions · 2024-04-22T19:00:38Z

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

KristijanZic changed the title ~~AppBar shape clipper disappears when scrolling~~ AppBar shape disappears on AppBar elevation change when scrolling Mar 29, 2024

huycozy added the in triage Presently being triaged by the triage team label Mar 29, 2024

HansMuller added P2 Important issues not at the top of the work list triaged-design Triaged by Design Languages team labels Apr 3, 2024

TahaTesser self-assigned this Apr 4, 2024

TahaTesser added the d: examples Sample code and demos label Apr 5, 2024

TahaTesser mentioned this issue Apr 8, 2024

Add a custom shape example for AppBar.shape #146421

Merged

9 tasks

Piinks added the d: api docs Issues with https://api.flutter.dev/ label Apr 8, 2024

auto-submit bot closed this as completed in #146421 Apr 8, 2024

TahaTesser added the r: fixed Issue is closed as already fixed in a newer version label Apr 8, 2024

github-actions bot locked as resolved and limited conversation to collaborators Apr 22, 2024

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

AppBar shape disappears on AppBar elevation change when scrolling #145945

AppBar shape disappears on AppBar elevation change when scrolling #145945

KristijanZic commented Mar 29, 2024 •

edited

Loading

KristijanZic commented Mar 29, 2024 •

edited

Loading

huycozy commented Mar 29, 2024

HansMuller commented Apr 3, 2024

TahaTesser commented Apr 5, 2024 •

edited

Loading

TahaTesser commented Apr 5, 2024 •

edited

Loading

HansMuller commented Apr 5, 2024 •

edited

Loading

KristijanZic commented Apr 6, 2024

TahaTesser commented Apr 8, 2024 •

edited

Loading

github-actions bot commented Apr 22, 2024

AppBar shape disappears on AppBar elevation change when scrolling #145945

AppBar shape disappears on AppBar elevation change when scrolling #145945

Comments

KristijanZic commented Mar 29, 2024 • edited Loading

Steps to reproduce

Expected results

Actual results

Code sample

Screenshots or Video

Logs

Flutter Doctor output

KristijanZic commented Mar 29, 2024 • edited Loading

huycozy commented Mar 29, 2024

HansMuller commented Apr 3, 2024

TahaTesser commented Apr 5, 2024 • edited Loading

Fixed code sample for AppBar

Preview

TahaTesser commented Apr 5, 2024 • edited Loading

HansMuller commented Apr 5, 2024 • edited Loading

KristijanZic commented Apr 6, 2024

TahaTesser commented Apr 8, 2024 • edited Loading

github-actions bot commented Apr 22, 2024

KristijanZic commented Mar 29, 2024 •

edited

Loading

KristijanZic commented Mar 29, 2024 •

edited

Loading

TahaTesser commented Apr 5, 2024 •

edited

Loading

Fixed code sample for `AppBar`

TahaTesser commented Apr 5, 2024 •

edited

Loading

HansMuller commented Apr 5, 2024 •

edited

Loading

TahaTesser commented Apr 8, 2024 •

edited

Loading