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Fix Scrollable TabBar for Material 3 (#131409)
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fixes [Material 3 `TabBar` does not take full width when `isScrollable: true`](flutter/flutter#117722)

### Description
1. Fixed the divider doesn't stretch to take all the available width in the scrollable tab bar in M3
2. Added `dividerHeight` property.

### Code sample

<details> 
<summary>expand to view the code sample</summary> 

```dart
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(
      debugShowCheckedModeBanner: false,
      home: TabBarExample(),
    );
  }
}

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

  @OverRide
  State<TabBarExample> createState() => _TabBarExampleState();
}

class _TabBarExampleState extends State<TabBarExample> {
  bool rtl = false;
  bool customColors = false;
  bool removeDivider = false;
  Color dividerColor = Colors.amber;
  Color indicatorColor = Colors.red;

  @OverRide
  Widget build(BuildContext context) {
    return DefaultTabController(
      initialIndex: 1,
      length: 3,
      child: Directionality(
        textDirection: rtl ? TextDirection.rtl : TextDirection.ltr,
        child: Scaffold(
          appBar: AppBar(
            title: const Text('TabBar Sample'),
            actions: <Widget>[
              IconButton.filledTonal(
                tooltip: 'Switch direction',
                icon: const Icon(Icons.swap_horiz),
                onPressed: () {
                  setState(() {
                    rtl = !rtl;
                  });
                },
              ),
              IconButton.filledTonal(
                tooltip: 'Use custom colors',
                icon: const Icon(Icons.color_lens),
                onPressed: () {
                  setState(() {
                    customColors = !customColors;
                  });
                },
              ),
              IconButton.filledTonal(
                tooltip: 'Show/hide divider',
                icon: const Icon(Icons.remove_rounded),
                onPressed: () {
                  setState(() {
                    removeDivider = !removeDivider;
                  });
                },
              ),
            ],
          ),
          body: Column(
            children: <Widget>[
              const Spacer(),
              const Text('Scrollable - TabAlignment.start'),
              TabBar(
                isScrollable: true,
                tabAlignment: TabAlignment.start,
                dividerColor: customColors ? dividerColor : null,
                indicatorColor: customColors ? indicatorColor : null,
                dividerHeight: removeDivider ? 0 : null,
                tabs: const <Widget>[
                  Tab(
                    icon: Icon(Icons.cloud_outlined),
                  ),
                  Tab(
                    icon: Icon(Icons.beach_access_sharp),
                  ),
                  Tab(
                    icon: Icon(Icons.brightness_5_sharp),
                  ),
                ],
              ),
              const Text('Scrollable - TabAlignment.startOffset'),
              TabBar(
                isScrollable: true,
                tabAlignment: TabAlignment.startOffset,
                dividerColor: customColors ? dividerColor : null,
                indicatorColor: customColors ? indicatorColor : null,
                dividerHeight: removeDivider ? 0 : null,
                tabs: const <Widget>[
                  Tab(
                    icon: Icon(Icons.cloud_outlined),
                  ),
                  Tab(
                    icon: Icon(Icons.beach_access_sharp),
                  ),
                  Tab(
                    icon: Icon(Icons.brightness_5_sharp),
                  ),
                ],
              ),
              const Text('Scrollable - TabAlignment.center'),
              TabBar(
                isScrollable: true,
                tabAlignment: TabAlignment.center,
                dividerColor: customColors ? dividerColor : null,
                indicatorColor: customColors ? indicatorColor : null,
                dividerHeight: removeDivider ? 0 : null,
                tabs: const <Widget>[
                  Tab(
                    icon: Icon(Icons.cloud_outlined),
                  ),
                  Tab(
                    icon: Icon(Icons.beach_access_sharp),
                  ),
                  Tab(
                    icon: Icon(Icons.brightness_5_sharp),
                  ),
                ],
              ),
              const Spacer(),
              const Text('Non-scrollable - TabAlignment.fill'),
              TabBar(
                tabAlignment: TabAlignment.fill,
                dividerColor: customColors ? dividerColor : null,
                indicatorColor: customColors ? indicatorColor : null,
                dividerHeight: removeDivider ? 0 : null,
                tabs: const <Widget>[
                  Tab(
                    icon: Icon(Icons.cloud_outlined),
                  ),
                  Tab(
                    icon: Icon(Icons.beach_access_sharp),
                  ),
                  Tab(
                    icon: Icon(Icons.brightness_5_sharp),
                  ),
                ],
              ),
              const Text('Non-scrollable - TabAlignment.center'),
              TabBar(
                tabAlignment: TabAlignment.center,
                dividerColor: customColors ? dividerColor : null,
                indicatorColor: customColors ? indicatorColor : null,
                dividerHeight: removeDivider ? 0 : null,
                tabs: const <Widget>[
                  Tab(
                    icon: Icon(Icons.cloud_outlined),
                  ),
                  Tab(
                    icon: Icon(Icons.beach_access_sharp),
                  ),
                  Tab(
                    icon: Icon(Icons.brightness_5_sharp),
                  ),
                ],
              ),
              const Spacer(),
              const Text('Secondary - TabAlignment.fill'),
              TabBar.secondary(
                tabAlignment: TabAlignment.fill,
                dividerColor: customColors ? dividerColor : null,
                indicatorColor: customColors ? indicatorColor : null,
                dividerHeight: removeDivider ? 0 : null,
                tabs: const <Widget>[
                  Tab(
                    icon: Icon(Icons.cloud_outlined),
                  ),
                  Tab(
                    icon: Icon(Icons.beach_access_sharp),
                  ),
                  Tab(
                    icon: Icon(Icons.brightness_5_sharp),
                  ),
                ],
              ),
              const Text('Secondary - TabAlignment.center'),
              TabBar.secondary(
                tabAlignment: TabAlignment.center,
                dividerColor: customColors ? dividerColor : null,
                indicatorColor: customColors ? indicatorColor : null,
                dividerHeight: removeDivider ? 0 : null,
                tabs: const <Widget>[
                  Tab(
                    icon: Icon(Icons.cloud_outlined),
                  ),
                  Tab(
                    icon: Icon(Icons.beach_access_sharp),
                  ),
                  Tab(
                    icon: Icon(Icons.brightness_5_sharp),
                  ),
                ],
              ),
              const Spacer(),
            ],
          ),
        ),
      ),
    );
  }
}
``` 
	
</details>

### Before

![Screenshot 2023-07-27 at 14 12 36](https://github.com/flutter/flutter/assets/48603081/1c08a9d2-ac15-4d33-8fa1-c765b4b10f92)

### After 

![Screenshot 2023-07-27 at 14 13 12](https://github.com/flutter/flutter/assets/48603081/7e662dfe-9f32-46c9-a128-3024a4782882)

This also contains regression test for flutter/flutter#125974 (comment)

```dart
  // This is a regression test for flutter/flutter#125974 (comment).
  testWidgets('Divider can be constrained', (WidgetTester tester) async {
```

![Screenshot 2023-07-27 at 14 16 37](https://github.com/flutter/flutter/assets/48603081/ac2ef49b-2410-46d0-8ae2-d9b77236abba)
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@TahaTesser
TahaTesser authored Aug 2, 2023
1 parent 9c471a9 commit 2c71881
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Showing 6 changed files with 967 additions and 95 deletions.
2 changes: 2 additions & 0 deletions dev/tools/gen_defaults/generated/used_tokens.csv
View file
Original file line number Diff line number Diff line change
Expand Up @@ -530,6 +530,7 @@ md.comp.primary-navigation-tab.active.hover.state-layer.opacity,
md.comp.primary-navigation-tab.active.pressed.state-layer.color,
md.comp.primary-navigation-tab.active.pressed.state-layer.opacity,
md.comp.primary-navigation-tab.divider.color,
md.comp.primary-navigation-tab.divider.height,
md.comp.primary-navigation-tab.inactive.focus.state-layer.color,
md.comp.primary-navigation-tab.inactive.focus.state-layer.opacity,
md.comp.primary-navigation-tab.inactive.hover.state-layer.color,
Expand Down Expand Up @@ -589,6 +590,7 @@ md.comp.search-view.header.supporting-text.color,
md.comp.search-view.header.supporting-text.text-style,
md.comp.secondary-navigation-tab.active.label-text.color,
md.comp.secondary-navigation-tab.divider.color,
md.comp.secondary-navigation-tab.divider.height,
md.comp.secondary-navigation-tab.focus.state-layer.color,
md.comp.secondary-navigation-tab.focus.state-layer.opacity,
md.comp.secondary-navigation-tab.hover.state-layer.color,
Expand Down
10 changes: 8 additions & 2 deletions dev/tools/gen_defaults/lib/tabs_template.dart
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,9 @@ class _${blockName}PrimaryDefaultsM3 extends TabBarTheme {
@override
Color? get dividerColor => ${componentColor("md.comp.primary-navigation-tab.divider")};
@override
double? get dividerHeight => ${getToken('md.comp.primary-navigation-tab.divider.height')};
@override
Color? get indicatorColor => ${componentColor("md.comp.primary-navigation-tab.active-indicator")};
Expand Down Expand Up @@ -71,7 +74,7 @@ class _${blockName}PrimaryDefaultsM3 extends TabBarTheme {
InteractiveInkFeatureFactory? get splashFactory => Theme.of(context).splashFactory;
@override
TabAlignment? get tabAlignment => isScrollable ? TabAlignment.start : TabAlignment.fill;
TabAlignment? get tabAlignment => isScrollable ? TabAlignment.startOffset : TabAlignment.fill;
static double indicatorWeight = ${getToken('md.comp.primary-navigation-tab.active-indicator.height')};
}
Expand All @@ -88,6 +91,9 @@ class _${blockName}SecondaryDefaultsM3 extends TabBarTheme {
@override
Color? get dividerColor => ${componentColor("md.comp.secondary-navigation-tab.divider")};
@override
double? get dividerHeight => ${getToken('md.comp.secondary-navigation-tab.divider.height')};
@override
Color? get indicatorColor => ${componentColor("md.comp.primary-navigation-tab.active-indicator")};
Expand Down Expand Up @@ -135,7 +141,7 @@ class _${blockName}SecondaryDefaultsM3 extends TabBarTheme {
InteractiveInkFeatureFactory? get splashFactory => Theme.of(context).splashFactory;
@override
TabAlignment? get tabAlignment => isScrollable ? TabAlignment.start : TabAlignment.fill;
TabAlignment? get tabAlignment => isScrollable ? TabAlignment.startOffset : TabAlignment.fill;
}
''';

Expand Down
9 changes: 9 additions & 0 deletions packages/flutter/lib/src/material/tab_bar_theme.dart
View file
Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ class TabBarTheme with Diagnosticable {
this.indicatorColor,
this.indicatorSize,
this.dividerColor,
this.dividerHeight,
this.labelColor,
this.labelPadding,
this.labelStyle,
Expand All @@ -55,6 +56,9 @@ class TabBarTheme with Diagnosticable {
/// Overrides the default value for [TabBar.dividerColor].
final Color? dividerColor;

/// Overrides the default value for [TabBar.dividerHeight].
final double? dividerHeight;

/// Overrides the default value for [TabBar.labelColor].
///
/// If [labelColor] is a [MaterialStateColor], then the effective color will
Expand Down Expand Up @@ -101,6 +105,7 @@ class TabBarTheme with Diagnosticable {
Color? indicatorColor,
TabBarIndicatorSize? indicatorSize,
Color? dividerColor,
double? dividerHeight,
Color? labelColor,
EdgeInsetsGeometry? labelPadding,
TextStyle? labelStyle,
Expand All @@ -116,6 +121,7 @@ class TabBarTheme with Diagnosticable {
indicatorColor: indicatorColor ?? this.indicatorColor,
indicatorSize: indicatorSize ?? this.indicatorSize,
dividerColor: dividerColor ?? this.dividerColor,
dividerHeight: dividerHeight ?? this.dividerHeight,
labelColor: labelColor ?? this.labelColor,
labelPadding: labelPadding ?? this.labelPadding,
labelStyle: labelStyle ?? this.labelStyle,
Expand Down Expand Up @@ -147,6 +153,7 @@ class TabBarTheme with Diagnosticable {
indicatorColor: Color.lerp(a.indicatorColor, b.indicatorColor, t),
indicatorSize: t < 0.5 ? a.indicatorSize : b.indicatorSize,
dividerColor: Color.lerp(a.dividerColor, b.dividerColor, t),
dividerHeight: t < 0.5 ? a.dividerHeight : b.dividerHeight,
labelColor: Color.lerp(a.labelColor, b.labelColor, t),
labelPadding: EdgeInsetsGeometry.lerp(a.labelPadding, b.labelPadding, t),
labelStyle: TextStyle.lerp(a.labelStyle, b.labelStyle, t),
Expand All @@ -165,6 +172,7 @@ class TabBarTheme with Diagnosticable {
indicatorColor,
indicatorSize,
dividerColor,
dividerHeight,
labelColor,
labelPadding,
labelStyle,
Expand All @@ -189,6 +197,7 @@ class TabBarTheme with Diagnosticable {
&& other.indicatorColor == indicatorColor
&& other.indicatorSize == indicatorSize
&& other.dividerColor == dividerColor
&& other.dividerHeight == dividerHeight
&& other.labelColor == labelColor
&& other.labelPadding == labelPadding
&& other.labelStyle == labelStyle
Expand Down
98 changes: 87 additions & 11 deletions packages/flutter/lib/src/material/tabs.dart
View file
Original file line number Diff line number Diff line change
Expand Up @@ -387,6 +387,39 @@ double _indexChangeProgress(TabController controller) {
return (controllerValue - currentIndex).abs() / (currentIndex - previousIndex).abs();
}

class _DividerPainter extends CustomPainter {
_DividerPainter({
required this.dividerColor,
required this.dividerHeight,
});

final Color dividerColor;
final double dividerHeight;

@override
void paint(Canvas canvas, Size size) {
if (dividerHeight <= 0.0) {
return;
}

final Paint paint = Paint()
..color = dividerColor
..strokeWidth = dividerHeight;

canvas.drawLine(
Offset(0, size.height - (paint.strokeWidth / 2)),
Offset(size.width, size.height - (paint.strokeWidth / 2)),
paint,
);
}

@override
bool shouldRepaint(_DividerPainter oldDelegate) {
return oldDelegate.dividerColor != dividerColor
|| oldDelegate.dividerHeight != dividerHeight;
}
}

class _IndicatorPainter extends CustomPainter {
_IndicatorPainter({
required this.controller,
Expand All @@ -397,6 +430,8 @@ class _IndicatorPainter extends CustomPainter {
required this.indicatorPadding,
required this.labelPaddings,
this.dividerColor,
this.dividerHeight,
required this.showDivider,
}) : super(repaint: controller.animation) {
if (old != null) {
saveTabOffsets(old._currentTabOffsets, old._currentTextDirection);
Expand All @@ -408,8 +443,10 @@ class _IndicatorPainter extends CustomPainter {
final TabBarIndicatorSize? indicatorSize;
final EdgeInsetsGeometry indicatorPadding;
final List<GlobalKey> tabKeys;
final Color? dividerColor;
final List<EdgeInsetsGeometry> labelPaddings;
final Color? dividerColor;
final double? dividerHeight;
final bool showDivider;

// _currentTabOffsets and _currentTextDirection are set each time TabBar
// layout is completed. These values can be null when TabBar contains no
Expand Down Expand Up @@ -501,9 +538,11 @@ class _IndicatorPainter extends CustomPainter {
size: _currentRect!.size,
textDirection: _currentTextDirection,
);
if (dividerColor != null) {
final Paint dividerPaint = Paint()..color = dividerColor!..strokeWidth = 1;
canvas.drawLine(Offset(0, size.height), Offset(size.width, size.height), dividerPaint);
if (showDivider && dividerHeight !> 0) {
final Paint dividerPaint = Paint()..color = dividerColor!..strokeWidth = dividerHeight!;
final Offset dividerP1 = Offset(0, size.height - (dividerPaint.strokeWidth / 2));
final Offset dividerP2 = Offset(size.width, size.height - (dividerPaint.strokeWidth / 2));
canvas.drawLine(dividerP1, dividerP2, dividerPaint);
}
_painter!.paint(canvas, _currentRect!.topLeft, configuration);
}
Expand Down Expand Up @@ -718,6 +757,7 @@ class TabBar extends StatefulWidget implements PreferredSizeWidget {
this.indicator,
this.indicatorSize,
this.dividerColor,
this.dividerHeight,
this.labelColor,
this.labelStyle,
this.labelPadding,
Expand Down Expand Up @@ -768,6 +808,7 @@ class TabBar extends StatefulWidget implements PreferredSizeWidget {
this.indicator,
this.indicatorSize,
this.dividerColor,
this.dividerHeight,
this.labelColor,
this.labelStyle,
this.labelPadding,
Expand Down Expand Up @@ -895,6 +936,13 @@ class TabBar extends StatefulWidget implements PreferredSizeWidget {
/// [ColorScheme.surfaceVariant] will be used, otherwise divider will not be drawn.
final Color? dividerColor;

/// The height of the divider.
///
/// If null and [ThemeData.useMaterial3] is true, [TabBarTheme.dividerHeight] is used.
/// If that is also null and [ThemeData.useMaterial3] is true, 1.0 will be used.
/// Otherwise divider will not be drawn.
final double? dividerHeight;

/// The color of selected tab labels.
///
/// If null, then [TabBarTheme.labelColor] is used. If that is also null and
Expand Down Expand Up @@ -1154,8 +1202,8 @@ class _TabBarState extends State<TabBar> {
TabBarTheme get _defaults {
if (Theme.of(context).useMaterial3) {
return widget._isPrimary
? _TabsPrimaryDefaultsM3(context, widget.isScrollable)
: _TabsSecondaryDefaultsM3(context, widget.isScrollable);
? _TabsPrimaryDefaultsM3(context, widget.isScrollable)
: _TabsSecondaryDefaultsM3(context, widget.isScrollable);
} else {
return _TabsDefaultsM2(context, widget.isScrollable);
}
Expand Down Expand Up @@ -1269,8 +1317,10 @@ class _TabBarState extends State<TabBar> {
indicatorPadding: widget.indicatorPadding,
tabKeys: _tabKeys,
old: _indicatorPainter,
dividerColor: theme.useMaterial3 ? widget.dividerColor ?? tabBarTheme.dividerColor ?? _defaults.dividerColor : null,
labelPaddings: _labelPaddings,
dividerColor: widget.dividerColor ?? tabBarTheme.dividerColor ?? _defaults.dividerColor,
dividerHeight: widget.dividerHeight ?? tabBarTheme.dividerHeight ?? _defaults.dividerHeight,
showDivider: theme.useMaterial3 && !widget.isScrollable,
);
}

Expand Down Expand Up @@ -1299,7 +1349,9 @@ class _TabBarState extends State<TabBar> {
widget.indicatorWeight != oldWidget.indicatorWeight ||
widget.indicatorSize != oldWidget.indicatorSize ||
widget.indicatorPadding != oldWidget.indicatorPadding ||
widget.indicator != oldWidget.indicator) {
widget.indicator != oldWidget.indicator ||
widget.dividerColor != oldWidget.dividerColor ||
widget.dividerHeight != oldWidget.dividerHeight) {
_initIndicatorPainter();
}

Expand Down Expand Up @@ -1475,6 +1527,7 @@ class _TabBarState extends State<TabBar> {
Widget build(BuildContext context) {
assert(debugCheckHasMaterialLocalizations(context));
assert(_debugScheduleCheckHasValidTabsCount());
final ThemeData theme = Theme.of(context);
final TabBarTheme tabBarTheme = TabBarTheme.of(context);
final TabAlignment effectiveTabAlignment = widget.tabAlignment ?? tabBarTheme.tabAlignment ?? _defaults.tabAlignment!;
assert(_debugTabAlignmentIsValid(effectiveTabAlignment));
Expand All @@ -1486,7 +1539,6 @@ class _TabBarState extends State<TabBar> {
);
}


final List<Widget> wrappedTabs = List<Widget>.generate(widget.tabs.length, (int index) {
const double verticalAdjustment = (_kTextAndIconTabHeight - _kTabHeight)/2.0;
EdgeInsetsGeometry? adjustedPadding;
Expand Down Expand Up @@ -1627,6 +1679,24 @@ class _TabBarState extends State<TabBar> {
child: tabBar,
),
);
if (theme.useMaterial3) {
final AlignmentGeometry effectiveAlignment = switch (effectiveTabAlignment) {
TabAlignment.center => Alignment.center,
TabAlignment.start || TabAlignment.startOffset || TabAlignment.fill => AlignmentDirectional.centerStart,
};

tabBar = CustomPaint(
painter: _DividerPainter(
dividerColor: widget.dividerColor ?? tabBarTheme.dividerColor ?? _defaults.dividerColor!,
dividerHeight: widget.dividerHeight ?? tabBarTheme.dividerHeight ?? _defaults.dividerHeight!,
),
child: Align(
heightFactor: 1.0,
alignment: effectiveAlignment,
child: tabBar,
),
);
}
} else if (widget.padding != null) {
tabBar = Padding(
padding: widget.padding!,
Expand Down Expand Up @@ -2177,6 +2247,9 @@ class _TabsPrimaryDefaultsM3 extends TabBarTheme {
@override
Color? get dividerColor => _colors.surfaceVariant;

@override
double? get dividerHeight => 1.0;

@override
Color? get indicatorColor => _colors.primary;

Expand Down Expand Up @@ -2224,7 +2297,7 @@ class _TabsPrimaryDefaultsM3 extends TabBarTheme {
InteractiveInkFeatureFactory? get splashFactory => Theme.of(context).splashFactory;

@override
TabAlignment? get tabAlignment => isScrollable ? TabAlignment.start : TabAlignment.fill;
TabAlignment? get tabAlignment => isScrollable ? TabAlignment.startOffset : TabAlignment.fill;

static double indicatorWeight = 3.0;
}
Expand All @@ -2241,6 +2314,9 @@ class _TabsSecondaryDefaultsM3 extends TabBarTheme {
@override
Color? get dividerColor => _colors.surfaceVariant;

@override
double? get dividerHeight => 1.0;

@override
Color? get indicatorColor => _colors.primary;

Expand Down Expand Up @@ -2288,7 +2364,7 @@ class _TabsSecondaryDefaultsM3 extends TabBarTheme {
InteractiveInkFeatureFactory? get splashFactory => Theme.of(context).splashFactory;

@override
TabAlignment? get tabAlignment => isScrollable ? TabAlignment.start : TabAlignment.fill;
TabAlignment? get tabAlignment => isScrollable ? TabAlignment.startOffset : TabAlignment.fill;
}

// END GENERATED TOKEN PROPERTIES - Tabs
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