Update `ExpansionTile` to support Material 3 & add an example (#119712)

dev/tools/gen_defaults/bin/gen_defaults.dart

@@ -31,6 +31,7 @@ import 'package:gen_defaults/date_picker_template.dart';
 import 'package:gen_defaults/dialog_template.dart';
 import 'package:gen_defaults/divider_template.dart';
 import 'package:gen_defaults/drawer_template.dart';
+import 'package:gen_defaults/expansion_tile_template.dart';
 import 'package:gen_defaults/fab_template.dart';
 import 'package:gen_defaults/filter_chip_template.dart';
 import 'package:gen_defaults/icon_button_template.dart';
@@ -153,6 +154,7 @@ Future<void> main(List<String> args) async {
   DialogTemplate('Dialog', '$materialLib/dialog.dart', tokens).updateFile();
   DividerTemplate('Divider', '$materialLib/divider.dart', tokens).updateFile();
   DrawerTemplate('Drawer', '$materialLib/drawer.dart', tokens).updateFile();
+  ExpansionTileTemplate('ExpansionTile', '$materialLib/expansion_tile.dart', tokens).updateFile();
   FABTemplate('FAB', '$materialLib/floating_action_button.dart', tokens).updateFile();
   FilterChipTemplate('ChoiceChip', '$materialLib/choice_chip.dart', tokens).updateFile();
   FilterChipTemplate('FilterChip', '$materialLib/filter_chip.dart', tokens).updateFile();

dev/tools/gen_defaults/lib/expansion_tile_template.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'template.dart';
+
+class ExpansionTileTemplate extends TokenTemplate {
+  const ExpansionTileTemplate(super.blockName, super.fileName, super.tokens, {
+    super.colorSchemePrefix = '_colors.',
+  });
+
+  @override
+  String generate() => '''
+class _${blockName}DefaultsM3 extends ExpansionTileThemeData {
+  _${blockName}DefaultsM3(this.context);
+
+  final BuildContext context;
+  late final ThemeData _theme = Theme.of(context);
+  late final ColorScheme _colors = _theme.colorScheme;
+
+  @override
+  Color? get textColor => ${textStyle("md.comp.list.list-item.label-text")}!.color;
+
+  @override
+  Color? get iconColor => ${componentColor('md.comp.list.list-item.selected.trailing-icon')};
+
+  @override
+  Color? get collapsedTextColor => ${textStyle("md.comp.list.list-item.label-text")}!.color;
+
+  @override
+  Color? get collapsedIconColor => ${componentColor('md.comp.list.list-item.unselected.trailing-icon')};
+}
+''';
+}

examples/api/lib/material/expansion_tile/expansion_tile.0.dart

@@ -6,33 +6,31 @@
 
 import 'package:flutter/material.dart';
 
-void main() => runApp(const MyApp());
+void main() => runApp(const ExpansionTileApp());
 
-class MyApp extends StatelessWidget {
-  const MyApp({super.key});
-
-  static const String _title = 'Flutter Code Sample';
+class ExpansionTileApp extends StatelessWidget {
+  const ExpansionTileApp({super.key});
 
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
-      title: _title,
+      theme: ThemeData(useMaterial3: true),
       home: Scaffold(
-        appBar: AppBar(title: const Text(_title)),
-        body: const MyStatefulWidget(),
+        appBar: AppBar(title: const Text('ExpansionTile Sample')),
+        body: const ExpansionTileExample(),
       ),
     );
   }
 }
 
-class MyStatefulWidget extends StatefulWidget {
-  const MyStatefulWidget({super.key});
+class ExpansionTileExample extends StatefulWidget {
+  const ExpansionTileExample({super.key});
 
   @override
-  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
+  State<ExpansionTileExample> createState() => _ExpansionTileExampleState();
 }
 
-class _MyStatefulWidgetState extends State<MyStatefulWidget> {
+class _ExpansionTileExampleState extends State<ExpansionTileExample> {
   bool _customTileExpanded = false;
 
   @override
@@ -58,7 +56,9 @@ class _MyStatefulWidgetState extends State<MyStatefulWidget> {
             ListTile(title: Text('This is tile number 2')),
           ],
           onExpansionChanged: (bool expanded) {
-            setState(() => _customTileExpanded = expanded);
+            setState(() {
+              _customTileExpanded = expanded;
+            });
           },
         ),
         const ExpansionTile(

examples/api/test/material/expansion_tile/expansion_tile.0_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/expansion_tile/expansion_tile.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('When expansion tiles are expanded tile numbers are revealed', (WidgetTester tester) async {
+    const int totalTiles = 3;
+
+    await tester.pumpWidget(
+      const example.ExpansionTileApp(),
+    );
+
+    expect(find.byType(ExpansionTile), findsNWidgets(totalTiles));
+
+    const String tileOne = 'This is tile number 1';
+    expect(find.text(tileOne), findsNothing);
+
+    await tester.tap(find.text('ExpansionTile 1'));
+    await tester.pumpAndSettle();
+    expect(find.text(tileOne), findsOneWidget);
+
+    const String tileTwo = 'This is tile number 2';
+    expect(find.text(tileTwo), findsNothing);
+
+    await tester.tap(find.text('ExpansionTile 2'));
+    await tester.pumpAndSettle();
+    expect(find.text(tileTwo), findsOneWidget);
+
+    const String tileThree = 'This is tile number 3';
+    expect(find.text(tileThree), findsNothing);
+
+    await tester.tap(find.text('ExpansionTile 3'));
+    await tester.pumpAndSettle();
+    expect(find.text(tileThree), findsOneWidget);
+  });
+}

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

@@ -34,7 +34,8 @@ const Duration _kExpand = Duration(milliseconds: 200);
 /// to the [leading] and [trailing] properties of [ExpansionTile].
 ///
 /// {@tool dartpad}
-/// This example demonstrates different configurations of ExpansionTile.
+/// This example demonstrates how the [ExpansionTile] icon's location and appearance
+/// can be customized.
 ///
 /// ** See code in examples/api/lib/material/expansion_tile/expansion_tile.0.dart **
 /// {@end-tool}
@@ -216,7 +217,7 @@ class ExpansionTile extends StatefulWidget {
   /// Used to override to the [ListTileThemeData.iconColor].
   ///
   /// If this property is null then [ExpansionTileThemeData.iconColor] is used. If that
-  /// is also null then the value of [ListTileThemeData.iconColor] is used.
+  /// is also null then the value of [ColorScheme.primary] is used.
   ///
   /// See also:
   ///
@@ -227,6 +228,15 @@ class ExpansionTile extends StatefulWidget {
   /// The icon color of tile's expansion arrow icon when the sublist is collapsed.
   ///
   /// Used to override to the [ListTileThemeData.iconColor].
+  ///
+  /// If this property is null then [ExpansionTileThemeData.collapsedIconColor] is used. If that
+  /// is also null and [ThemeData.useMaterial3] is true, [ColorScheme.onSurface] is used. Otherwise,
+  /// defaults to [ThemeData.unselectedWidgetColor] color.
+  ///
+  /// See also:
+  ///
+  /// * [ExpansionTileTheme.of], which returns the nearest [ExpansionTileTheme]'s
+  ///   [ExpansionTileThemeData].
   final Color? collapsedIconColor;
 
 
@@ -235,7 +245,8 @@ class ExpansionTile extends StatefulWidget {
   /// Used to override to the [ListTileThemeData.textColor].
   ///
   /// If this property is null then [ExpansionTileThemeData.textColor] is used. If that
-  /// is also null then the value of [ListTileThemeData.textColor] is used.
+  /// is also null then and [ThemeData.useMaterial3] is true, color of the [TextTheme.bodyLarge]
+  /// will be used for the [title] and [subtitle]. Otherwise, defaults to [ColorScheme.primary] color.
   ///
   /// See also:
   ///
@@ -247,8 +258,10 @@ class ExpansionTile extends StatefulWidget {
   ///
   /// Used to override to the [ListTileThemeData.textColor].
   ///
-  /// If this property is null then [ExpansionTileThemeData.collapsedTextColor] is used. If that
-  /// is also null then the value of [ListTileThemeData.textColor] is used.
+  /// If this property is null then [ExpansionTileThemeData.collapsedTextColor] is used.
+  /// If that is also null and [ThemeData.useMaterial3] is true, color of the
+  /// [TextTheme.bodyLarge] will be used for the [title] and [subtitle]. Otherwise,
+  /// defaults to color of the [TextTheme.titleMedium].
   ///
   /// See also:
   ///
@@ -441,7 +454,9 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   void didChangeDependencies() {
     final ThemeData theme = Theme.of(context);
     final ExpansionTileThemeData expansionTileTheme = ExpansionTileTheme.of(context);
-    final ColorScheme colorScheme = theme.colorScheme;
+    final ExpansionTileThemeData defaults = theme.useMaterial3
+      ? _ExpansionTileDefaultsM3(context)
+      : _ExpansionTileDefaultsM2(context);
     _borderTween
       ..begin = widget.collapsedShape
         ?? expansionTileTheme.collapsedShape
@@ -458,13 +473,13 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
     _headerColorTween
       ..begin = widget.collapsedTextColor
         ?? expansionTileTheme.collapsedTextColor
-        ?? theme.textTheme.titleMedium!.color
-      ..end = widget.textColor ?? expansionTileTheme.textColor ?? colorScheme.primary;
+        ?? defaults.collapsedTextColor
+      ..end = widget.textColor ?? expansionTileTheme.textColor ?? defaults.textColor;
     _iconColorTween
       ..begin = widget.collapsedIconColor
         ?? expansionTileTheme.collapsedIconColor
-        ?? theme.unselectedWidgetColor
-      ..end = widget.iconColor ?? expansionTileTheme.iconColor ?? colorScheme.primary;
+        ?? defaults.collapsedIconColor
+      ..end = widget.iconColor ?? expansionTileTheme.iconColor ?? defaults.iconColor;
     _backgroundColorTween
       ..begin = widget.collapsedBackgroundColor ?? expansionTileTheme.collapsedBackgroundColor
       ..end = widget.backgroundColor ?? expansionTileTheme.backgroundColor;
@@ -498,3 +513,54 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
     );
   }
 }
+
+class _ExpansionTileDefaultsM2 extends ExpansionTileThemeData {
+  _ExpansionTileDefaultsM2(this.context);
+
+  final BuildContext context;
+  late final ThemeData _theme = Theme.of(context);
+  late final ColorScheme _colorScheme = _theme.colorScheme;
+
+  @override
+  Color? get textColor => _colorScheme.primary;
+
+  @override
+  Color? get iconColor => _colorScheme.primary;
+
+  @override
+  Color? get collapsedTextColor => _theme.textTheme.titleMedium!.color;
+
+  @override
+  Color? get collapsedIconColor => _theme.unselectedWidgetColor;
+}
+
+// BEGIN GENERATED TOKEN PROPERTIES - ExpansionTile
+
+// Do not edit by hand. The code between the "BEGIN GENERATED" and
+// "END GENERATED" comments are generated from data in the Material
+// Design token database by the script:
+//   dev/tools/gen_defaults/bin/gen_defaults.dart.
+
+// Token database version: v0_152
+
+class _ExpansionTileDefaultsM3 extends ExpansionTileThemeData {
+  _ExpansionTileDefaultsM3(this.context);
+
+  final BuildContext context;
+  late final ThemeData _theme = Theme.of(context);
+  late final ColorScheme _colors = _theme.colorScheme;
+
+  @override
+  Color? get textColor => Theme.of(context).textTheme.bodyLarge!.color;
+
+  @override
+  Color? get iconColor => _colors.primary;
+
+  @override
+  Color? get collapsedTextColor => Theme.of(context).textTheme.bodyLarge!.color;
+
+  @override
+  Color? get collapsedIconColor => _colors.onSurface;
+}
+
+// END GENERATED TOKEN PROPERTIES - ExpansionTile

packages/flutter/test/material/expansion_tile_test.dart

@@ -522,6 +522,35 @@ void main() {
     expect(shapeDecoration.color, backgroundColor);
   });
 
+  testWidgets('ExpansionTile default iconColor, textColor', (WidgetTester tester) async {
+    final ThemeData theme = ThemeData(useMaterial3: true);
+
+    await tester.pumpWidget(MaterialApp(
+      theme: theme,
+      home: const Material(
+        child: ExpansionTile(
+          title: TestText('title'),
+          trailing: TestIcon(),
+          children: <Widget>[
+            SizedBox(height: 100, width: 100),
+          ],
+        ),
+      ),
+    ));
+
+    Color getIconColor() => tester.state<TestIconState>(find.byType(TestIcon)).iconTheme.color!;
+    Color getTextColor() => tester.state<TestTextState>(find.byType(TestText)).textStyle.color!;
+
+    expect(getIconColor(), theme.colorScheme.onSurface);
+    expect(getTextColor(), theme.textTheme.bodyLarge!.color);
+
+    await tester.tap(find.text('title'));
+    await tester.pumpAndSettle();
+
+    expect(getIconColor(), theme.colorScheme.primary);
+    expect(getTextColor(), theme.textTheme.bodyLarge!.color);
+  });
+
   testWidgets('ExpansionTile iconColor, textColor', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/pull/78281
 
@@ -666,4 +695,38 @@ void main() {
     expect(listTile.leading.runtimeType, Icon);
     expect(listTile.trailing, isNull);
   });
+
+  group('Material 2', () {
+    // Tests that are only relevant for Material 2. Once ThemeData.useMaterial3
+    // is turned on by default, these tests can be removed.
+
+    testWidgets('ExpansionTile default iconColor, textColor', (WidgetTester tester) async {
+      final ThemeData theme = ThemeData(useMaterial3: false);
+
+      await tester.pumpWidget(MaterialApp(
+        theme: theme,
+        home: const Material(
+          child: ExpansionTile(
+            title: TestText('title'),
+            trailing: TestIcon(),
+            children: <Widget>[
+              SizedBox(height: 100, width: 100),
+            ],
+          ),
+        ),
+      ));
+
+      Color getIconColor() => tester.state<TestIconState>(find.byType(TestIcon)).iconTheme.color!;
+      Color getTextColor() => tester.state<TestTextState>(find.byType(TestText)).textStyle.color!;
+
+      expect(getIconColor(), theme.unselectedWidgetColor);
+      expect(getTextColor(), theme.textTheme.titleMedium!.color);
+
+      await tester.tap(find.text('title'));
+      await tester.pumpAndSettle();
+
+      expect(getIconColor(), theme.colorScheme.primary);
+      expect(getTextColor(), theme.colorScheme.primary);
+    });
+  });
 }