Adaptive `Switch` (#130425)

Currently, `Switch.factory` delegates to `CupertinoSwitch` when platform
is iOS or macOS. This PR is to:
* have the factory configure the Material `Switch` for the expected look
and feel.
* introduce `Adaptation` class to customize themes for the adaptive
components.

dev/tools/gen_defaults/lib/switch_template.dart

@@ -126,6 +126,12 @@ class _${blockName}DefaultsM3 extends SwitchThemeData {
     });
   }
 
+  @override
+  MaterialStateProperty<MouseCursor> get mouseCursor {
+    return MaterialStateProperty.resolveWith((Set<MaterialState> states)
+      => MaterialStateMouseCursor.clickable.resolve(states));
+  }
+
   @override
   MaterialStatePropertyAll<double> get trackOutlineWidth => const MaterialStatePropertyAll<double>(${getToken('md.comp.switch.track.outline.width')});
 

examples/api/lib/material/switch/switch.4.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';
+
+/// Flutter code sample for [Switch.adaptive].
+
+void main() => runApp(const SwitchApp());
+
+class SwitchApp extends StatefulWidget {
+  const SwitchApp({super.key});
+
+  @override
+  State<SwitchApp> createState() => _SwitchAppState();
+}
+
+class _SwitchAppState extends State<SwitchApp> {
+  bool isMaterial = true;
+  bool isCustomized = false;
+
+  @override
+  Widget build(BuildContext context) {
+    final ThemeData theme = ThemeData(
+      platform: isMaterial ? TargetPlatform.android : TargetPlatform.iOS,
+      adaptations: <Adaptation<Object>>[
+        if (isCustomized) const _SwitchThemeAdaptation()
+      ]
+    );
+    final ButtonStyle style = OutlinedButton.styleFrom(
+      fixedSize: const Size(220, 40),
+    );
+
+    return MaterialApp(
+      theme: theme,
+      home: Scaffold(
+        appBar: AppBar(title: const Text('Adaptive Switches')),
+        body: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: <Widget>[
+            OutlinedButton(
+              style: style,
+              onPressed: () {
+                setState(() {
+                  isMaterial = !isMaterial;
+                });
+              },
+              child: isMaterial ? const Text('Show cupertino style') : const Text('Show material style'),
+            ),
+            OutlinedButton(
+              style: style,
+              onPressed: () {
+                setState(() {
+                  isCustomized = !isCustomized;
+                });
+              },
+              child: isCustomized ? const Text('Remove customization') : const Text('Add customization'),
+            ),
+            const SizedBox(height: 20),
+            const SwitchWithLabel(label: 'enabled', enabled: true),
+            const SwitchWithLabel(label: 'disabled', enabled: false),
+          ],
+        ),
+      ),
+    );
+  }
+}
+
+class SwitchWithLabel extends StatefulWidget {
+  const SwitchWithLabel({
+    super.key,
+    required this.enabled,
+    required this.label,
+  });
+
+  final bool enabled;
+  final String label;
+
+  @override
+  State<SwitchWithLabel> createState() => _SwitchWithLabelState();
+}
+
+class _SwitchWithLabelState extends State<SwitchWithLabel> {
+  bool active = true;
+
+  @override
+  Widget build(BuildContext context) {
+    return Row(
+      mainAxisAlignment: MainAxisAlignment.center,
+      children: <Widget>[
+        Container(
+          width: 150,
+          padding: const EdgeInsets.only(right: 20),
+          child: Text(widget.label)
+        ),
+        Switch.adaptive(
+          value: active,
+          onChanged: !widget.enabled ? null : (bool value) {
+            setState(() {
+              active = value;
+            });
+          },
+        ),
+      ],
+    );
+  }
+}
+
+
+class _SwitchThemeAdaptation extends Adaptation<SwitchThemeData> {
+  const _SwitchThemeAdaptation();
+
+  @override
+  SwitchThemeData adapt(ThemeData theme, SwitchThemeData defaultValue) {
+    switch (theme.platform) {
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        return defaultValue;
+      case TargetPlatform.iOS:
+      case TargetPlatform.macOS:
+        return SwitchThemeData(
+          thumbColor: MaterialStateProperty.resolveWith<Color?>((Set<MaterialState> states) {
+            if (states.contains(MaterialState.selected)) {
+              return Colors.yellow;
+            }
+            return null; // Use the default.
+          }),
+          trackColor: const MaterialStatePropertyAll<Color>(Colors.brown),
+        );
+    }
+  }
+}

examples/api/test/material/switch/switch.4_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/switch/switch.4.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Show adaptive switch theme', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.SwitchApp(),
+    );
+
+    // Default is material style switches
+    expect(find.text('Show cupertino style'), findsOneWidget);
+    expect(find.text('Show material style'), findsNothing);
+
+    Finder adaptiveSwitch = find.byType(Switch).first;
+    expect(
+      adaptiveSwitch,
+      paints
+        ..rrect(color: const Color(0xff6750a4)) // M3 primary color.
+        ..rrect()
+        ..rrect(color: Colors.white), // Thumb color
+    );
+
+    await tester.tap(find.widgetWithText(OutlinedButton, 'Add customization'));
+    await tester.pumpAndSettle();
+
+    // Theme adaptation does not affect material-style switch.
+    adaptiveSwitch = find.byType(Switch).first;
+    expect(
+      adaptiveSwitch,
+      paints
+        ..rrect(color: const Color(0xff6750a4)) // M3 primary color.
+        ..rrect()
+        ..rrect(color: Colors.white), // Thumb color
+    );
+
+    await tester.tap(find.widgetWithText(OutlinedButton, 'Show cupertino style'));
+    await tester.pumpAndSettle();
+
+    expect(
+      adaptiveSwitch,
+      paints
+        ..rrect(color: const Color(0xff795548)) // Customized track color only for cupertino.
+        ..rrect()..rrect()..rrect()..rrect()
+        ..rrect(color: const Color(0xffffeb3b)), // Customized thumb color only for cupertino.
+    );
+
+    await tester.tap(find.widgetWithText(OutlinedButton, 'Remove customization'));
+    await tester.pumpAndSettle();
+
+    expect(
+      adaptiveSwitch,
+      paints
+        ..rrect(color: const Color(0xff34c759)) // Cupertino system green.
+        ..rrect()..rrect()..rrect()..rrect()
+        ..rrect(color: Colors.white), // Thumb color
+    );
+  });
+}

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

@@ -73,6 +73,37 @@ export 'package:flutter/services.dart' show Brightness;
 // Examples can assume:
 // late BuildContext context;
 
+/// Defines a customized theme for components with an `adaptive` factory constructor.
+///
+/// Currently, only [Switch.adaptive] supports this class.
+class Adaptation<T> {
+  /// Creates an [Adaptation].
+  const Adaptation();
+
+  /// The adaptation's type.
+  Type get type => T;
+
+  /// Typically, this is overridden to return an instance of a custom component
+  /// ThemeData class, like [SwitchThemeData], instead of the defaultValue.
+  ///
+  /// Factory constructors that support adaptations - currently only
+  /// [Switch.adaptive] - look for a [ThemeData.adaptations] member of the expected
+  /// type when computing their effective default component theme. If a matching
+  /// adaptation is not found, the component may choose to use a default adaptation.
+  /// For example, the [Switch.adaptive] component uses an empty [SwitchThemeData]
+  /// if a matching adaptation is not found, for the sake of backwards compatibility.
+  ///
+  /// {@tool dartpad}
+  /// This sample shows how to create and use subclasses of [Adaptation] that
+  /// define adaptive [SwitchThemeData]s. The [adapt] method in this example is
+  /// overridden to only customize cupertino-style switches, but it can also be
+  /// used to customize any other platforms.
+  ///
+  /// ** See code in examples/api/lib/material/switch/switch.4.dart **
+  /// {@end-tool}
+  T adapt(ThemeData theme, T defaultValue) => defaultValue;
+}
+
 /// An interface that defines custom additions to a [ThemeData] object.
 ///
 /// {@youtube 560 315 https://www.youtube.com/watch?v=8-szcYzFVao}
@@ -241,6 +272,7 @@ class ThemeData with Diagnosticable {
     // alphabetical by symbol name.
 
     // GENERAL CONFIGURATION
+    Iterable<Adaptation<Object>>? adaptations,
     bool? applyElevationOverlayColor,
     NoDefaultCupertinoThemeData? cupertinoOverrideTheme,
     Iterable<ThemeExtension<dynamic>>? extensions,
@@ -366,6 +398,7 @@ class ThemeData with Diagnosticable {
     // GENERAL CONFIGURATION
     cupertinoOverrideTheme = cupertinoOverrideTheme?.noDefault();
     extensions ??= <ThemeExtension<dynamic>>[];
+    adaptations ??= <Adaptation<Object>>[];
     inputDecorationTheme ??= const InputDecorationTheme();
     platform ??= defaultTargetPlatform;
     switch (platform) {
@@ -551,6 +584,7 @@ class ThemeData with Diagnosticable {
       // alphabetical by symbol name.
 
       // GENERAL CONFIGURATION
+      adaptationMap: _createAdaptationMap(adaptations),
       applyElevationOverlayColor: applyElevationOverlayColor,
       cupertinoOverrideTheme: cupertinoOverrideTheme,
       extensions: _themeExtensionIterableToMap(extensions),
@@ -658,6 +692,7 @@ class ThemeData with Diagnosticable {
     // alphabetical by symbol name.
 
     // GENERAL CONFIGURATION
+    required this.adaptationMap,
     required this.applyElevationOverlayColor,
     required this.cupertinoOverrideTheme,
     required this.extensions,
@@ -871,6 +906,19 @@ class ThemeData with Diagnosticable {
   /// text geometry.
   factory ThemeData.fallback({bool? useMaterial3}) => ThemeData.light(useMaterial3: useMaterial3);
 
+  /// Used to obtain a particular [Adaptation] from [adaptationMap].
+  ///
+  /// To get an adaptation, use `Theme.of(context).getAdaptation<MyAdaptation>()`.
+  Adaptation<T>? getAdaptation<T>() => adaptationMap[T] as Adaptation<T>?;
+
+  static Map<Type, Adaptation<Object>> _createAdaptationMap(Iterable<Adaptation<Object>> adaptations) {
+    final Map<Type, Adaptation<Object>> adaptationMap = <Type, Adaptation<Object>>{
+      for (final Adaptation<Object> adaptation in adaptations)
+        adaptation.type: adaptation
+    };
+    return adaptationMap;
+  }
+
   /// The overall theme brightness.
   ///
   /// The default [TextStyle] color for the [textTheme] is black if the
@@ -960,6 +1008,12 @@ class ThemeData with Diagnosticable {
   /// See [extensions] for an interactive example.
   T? extension<T>() => extensions[T] as T?;
 
+  /// A map which contains the adaptations for the theme. The entry's key is the
+  /// type of the adaptation; the value is the adaptation itself.
+  ///
+  /// To obtain an adaptation, use [getAdaptation].
+  final Map<Type, Adaptation<Object>> adaptationMap;
+
   /// The default [InputDecoration] values for [InputDecorator], [TextField],
   /// and [TextFormField] are based on this theme.
   ///
@@ -1480,6 +1534,7 @@ class ThemeData with Diagnosticable {
     // alphabetical by symbol name.
 
     // GENERAL CONFIGURATION
+    Iterable<Adaptation<Object>>? adaptations,
     bool? applyElevationOverlayColor,
     NoDefaultCupertinoThemeData? cupertinoOverrideTheme,
     Iterable<ThemeExtension<dynamic>>? extensions,
@@ -1612,6 +1667,7 @@ class ThemeData with Diagnosticable {
       // alphabetical by symbol name.
 
       // GENERAL CONFIGURATION
+      adaptationMap: adaptations != null ? _createAdaptationMap(adaptations) : adaptationMap,
       applyElevationOverlayColor: applyElevationOverlayColor ?? this.applyElevationOverlayColor,
       cupertinoOverrideTheme: cupertinoOverrideTheme ?? this.cupertinoOverrideTheme,
       extensions: (extensions != null) ? _themeExtensionIterableToMap(extensions) : this.extensions,
@@ -1812,6 +1868,7 @@ class ThemeData with Diagnosticable {
       // alphabetical by symbol name.
 
       // GENERAL CONFIGURATION
+      adaptationMap: t < 0.5 ? a.adaptationMap : b.adaptationMap,
       applyElevationOverlayColor:t < 0.5 ? a.applyElevationOverlayColor : b.applyElevationOverlayColor,
       cupertinoOverrideTheme:t < 0.5 ? a.cupertinoOverrideTheme : b.cupertinoOverrideTheme,
       extensions: _lerpThemeExtensions(a, b, t),
@@ -1917,6 +1974,7 @@ class ThemeData with Diagnosticable {
         // alphabetical by symbol name.
 
         // GENERAL CONFIGURATION
+        mapEquals(other.adaptationMap, adaptationMap) &&
         other.applyElevationOverlayColor == applyElevationOverlayColor &&
         other.cupertinoOverrideTheme == cupertinoOverrideTheme &&
         mapEquals(other.extensions, extensions) &&
@@ -2018,6 +2076,8 @@ class ThemeData with Diagnosticable {
       // alphabetical by symbol name.
 
       // GENERAL CONFIGURATION
+      ...adaptationMap.keys,
+      ...adaptationMap.values,
       applyElevationOverlayColor,
       cupertinoOverrideTheme,
       ...extensions.keys,
@@ -2123,6 +2183,7 @@ class ThemeData with Diagnosticable {
     // alphabetical by symbol name.
 
     // GENERAL CONFIGURATION
+    properties.add(IterableProperty<Adaptation<dynamic>>('adaptations', adaptationMap.values, defaultValue: defaultData.adaptationMap.values, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<bool>('applyElevationOverlayColor', applyElevationOverlayColor, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<NoDefaultCupertinoThemeData>('cupertinoOverrideTheme', cupertinoOverrideTheme, defaultValue: defaultData.cupertinoOverrideTheme, level: DiagnosticLevel.debug));
     properties.add(IterableProperty<ThemeExtension<dynamic>>('extensions', extensions.values, defaultValue: defaultData.extensions.values, level: DiagnosticLevel.debug));

packages/flutter/test/material/switch_list_tile_test.dart

@@ -150,6 +150,7 @@ void main() {
       find.byType(Switch),
       paints
         ..rrect(color: Colors.blue[500])
+        ..rrect()
         ..rrect(color: const Color(0x33000000))
         ..rrect(color: const Color(0x24000000))
         ..rrect(color: const Color(0x1f000000))
@@ -163,6 +164,7 @@ void main() {
       Material.of(tester.element(find.byType(Switch))),
       paints
         ..rrect(color: Colors.green[500])
+        ..rrect()
         ..rrect(color: const Color(0x33000000))
         ..rrect(color: const Color(0x24000000))
         ..rrect(color: const Color(0x1f000000))
@@ -221,7 +223,7 @@ void main() {
     );
   });
 
-  testWidgetsWithLeakTracking('SwitchListTile.adaptive delegates to', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('SwitchListTile.adaptive only uses material switch', (WidgetTester tester) async {
     bool value = false;
 
     Widget buildFrame(TargetPlatform platform) {
@@ -246,23 +248,15 @@ void main() {
       );
     }
 
-    for (final TargetPlatform platform in <TargetPlatform>[ TargetPlatform.iOS, TargetPlatform.macOS ]) {
+    for (final TargetPlatform platform in <TargetPlatform>[ TargetPlatform.iOS,
+      TargetPlatform.macOS, TargetPlatform.android, TargetPlatform.fuchsia,
+      TargetPlatform.linux, TargetPlatform.windows ]) {
       value = false;
       await tester.pumpWidget(buildFrame(platform));
-      expect(find.byType(CupertinoSwitch), findsOneWidget);
-      expect(value, isFalse, reason: 'on ${platform.name}');
-
-      await tester.tap(find.byType(SwitchListTile));
-      expect(value, isTrue, reason: 'on ${platform.name}');
-    }
-
-    for (final TargetPlatform platform in <TargetPlatform>[ TargetPlatform.android, TargetPlatform.fuchsia, TargetPlatform.linux, TargetPlatform.windows ]) {
-      value = false;
-      await tester.pumpWidget(buildFrame(platform));
-      await tester.pumpAndSettle(); // Finish the theme change animation.
-
       expect(find.byType(CupertinoSwitch), findsNothing);
+      expect(find.byType(Switch), findsOneWidget);
       expect(value, isFalse, reason: 'on ${platform.name}');
+
       await tester.tap(find.byType(SwitchListTile));
       expect(value, isTrue, reason: 'on ${platform.name}');
     }
@@ -714,14 +708,14 @@ void main() {
     await tester.pumpAndSettle();
     expect(
       Material.of(tester.element(find.byType(Switch))),
-      paints..rrect()..rrect()..rrect()..rrect()..rrect(color: inactiveDisabledThumbColor)
+      paints..rrect()..rrect()..rrect()..rrect()..rrect()..rrect(color: inactiveDisabledThumbColor)
     );
 
     await tester.pumpWidget(buildSwitchListTile(enabled: false, selected: true));
     await tester.pumpAndSettle();
     expect(
       Material.of(tester.element(find.byType(Switch))),
-      paints..rrect()..rrect()..rrect()..rrect()..rrect(color: activeDisabledThumbColor)
+      paints..rrect()..rrect()..rrect()..rrect()..rrect()..rrect(color: activeDisabledThumbColor)
     );
 
     await tester.pumpWidget(buildSwitchListTile(enabled: true, selected: false));
@@ -729,7 +723,7 @@ void main() {
 
     expect(
       Material.of(tester.element(find.byType(Switch))),
-      paints..rrect()..rrect()..rrect()..rrect()..rrect(color: inactiveEnabledThumbColor)
+      paints..rrect()..rrect()..rrect()..rrect()..rrect()..rrect(color: inactiveEnabledThumbColor)
     );
 
     await tester.pumpWidget(buildSwitchListTile(enabled: true, selected: true));
@@ -737,7 +731,7 @@ void main() {
 
     expect(
       Material.of(tester.element(find.byType(Switch))),
-      paints..rrect()..rrect()..rrect()..rrect()..rrect(color: activeEnabledThumbColor)
+      paints..rrect()..rrect()..rrect()..rrect()..rrect()..rrect(color: activeEnabledThumbColor)
     );
   });
 
@@ -853,7 +847,7 @@ void main() {
 
     expect(
       Material.of(tester.element(find.byType(Switch))),
-      paints..rrect()..rrect()..rrect()..rrect()..rrect(color: hoveredThumbColor),
+      paints..rrect()..rrect()..rrect()..rrect()..rrect()..rrect(color: hoveredThumbColor),
     );
 
     // On pressed state
@@ -861,7 +855,7 @@ void main() {
     await tester.pumpAndSettle();
     expect(
       Material.of(tester.element(find.byType(Switch))),
-      paints..rrect()..rrect()..rrect()..rrect()..rrect(color: pressedThumbColor),
+      paints..rrect()..rrect()..rrect()..rrect()..rrect()..rrect(color: pressedThumbColor),
     );
   });
 
@@ -1188,7 +1182,7 @@ void main() {
     for (final TargetPlatform platform in <TargetPlatform>[ TargetPlatform.iOS, TargetPlatform.macOS ]) {
       await tester.pumpWidget(buildSwitchListTile(true, platform));
       await tester.pumpAndSettle();
-      expect(find.byType(CupertinoSwitch), findsOneWidget);
+      expect(find.byType(Switch), findsOneWidget);
       expect(
         Material.of(tester.element(find.byType(Switch))),
         paints..rrect(color: const Color(0xFF2196F3)),
@@ -1196,7 +1190,7 @@ void main() {
 
       await tester.pumpWidget(buildSwitchListTile(false, platform));
       await tester.pumpAndSettle();
-      expect(find.byType(CupertinoSwitch), findsOneWidget);
+      expect(find.byType(Switch), findsOneWidget);
       expect(
         Material.of(tester.element(find.byType(Switch))),
         paints..rrect(color: const Color(0xFF34C759)),
@@ -1224,7 +1218,7 @@ void main() {
     for (final TargetPlatform platform in <TargetPlatform>[ TargetPlatform.iOS, TargetPlatform.macOS ]) {
       await tester.pumpWidget(buildSwitchListTile(true, platform));
       await tester.pumpAndSettle();
-      expect(find.byType(CupertinoSwitch), findsOneWidget);
+      expect(find.byType(Switch), findsOneWidget);
       expect(
         Material.of(tester.element(find.byType(Switch))),
         paints..rrect(color: const Color(0xFF6750A4)),
@@ -1232,7 +1226,7 @@ void main() {
 
       await tester.pumpWidget(buildSwitchListTile(false, platform));
       await tester.pumpAndSettle();
-      expect(find.byType(CupertinoSwitch), findsOneWidget);
+      expect(find.byType(Switch), findsOneWidget);
       expect(
         Material.of(tester.element(find.byType(Switch))),
         paints..rrect(color: const Color(0xFF34C759)),

packages/flutter/test/material/switch_theme_test.dart

@@ -717,6 +717,7 @@ void main() {
         ..rrect()
         ..rrect()
         ..rrect()
+        ..rrect()
         ..rrect(color: defaultThumbColor)
     );
 
@@ -730,6 +731,7 @@ void main() {
         ..rrect()
         ..rrect()
         ..rrect()
+        ..rrect()
         ..rrect(color: selectedThumbColor)
     );
   });

packages/flutter/test/material/theme_data_test.dart

@@ -724,6 +724,7 @@ void main() {
       // alphabetical by symbol name.
 
       // GENERAL CONFIGURATION
+      adaptationMap: const <Type, Adaptation<Object>>{},
       applyElevationOverlayColor: false,
       cupertinoOverrideTheme: null,
       extensions: const <Object, ThemeExtension<dynamic>>{},
@@ -836,6 +837,9 @@ void main() {
       // alphabetical by symbol name.
 
       // GENERAL CONFIGURATION
+      adaptationMap: const <Type, Adaptation<Object>>{
+        SwitchThemeData: SwitchThemeAdaptation(),
+      },
       applyElevationOverlayColor: true,
       cupertinoOverrideTheme: ThemeData.light().cupertinoOverrideTheme,
       extensions: const <Object, ThemeExtension<dynamic>>{
@@ -941,6 +945,7 @@ void main() {
       // alphabetical by symbol name.
 
       // GENERAL CONFIGURATION
+      adaptations: otherTheme.adaptationMap.values,
       applyElevationOverlayColor: otherTheme.applyElevationOverlayColor,
       cupertinoOverrideTheme: otherTheme.cupertinoOverrideTheme,
       extensions: otherTheme.extensions.values,
@@ -1041,6 +1046,7 @@ void main() {
     // alphabetical by symbol name.
 
     // GENERAL CONFIGURATION
+    expect(themeDataCopy.adaptationMap, equals(otherTheme.adaptationMap));
     expect(themeDataCopy.applyElevationOverlayColor, equals(otherTheme.applyElevationOverlayColor));
     expect(themeDataCopy.cupertinoOverrideTheme, equals(otherTheme.cupertinoOverrideTheme));
     expect(themeDataCopy.extensions, equals(otherTheme.extensions));
@@ -1178,6 +1184,7 @@ void main() {
     // List of properties must match the properties in ThemeData.hashCode()
     final Set<String> expectedPropertyNames = <String>{
       // GENERAL CONFIGURATION
+      'adaptations',
       'applyElevationOverlayColor',
       'cupertinoOverrideTheme',
       'extensions',
@@ -1285,100 +1292,139 @@ void main() {
     expect(propertyNames, expectedPropertyNames);
   });
 
+  group('Theme adaptationMap', () {
+    const Key containerKey = Key('container');
+
+    testWidgetsWithLeakTracking('can be obtained', (WidgetTester tester) async {
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: ThemeData(
+            adaptations: const <Adaptation<Object>>[
+              StringAdaptation(),
+              SwitchThemeAdaptation()
+            ],
+          ),
+          home: Container(key: containerKey),
+        ),
+      );
+
+      final ThemeData theme = Theme.of(
+        tester.element(find.byKey(containerKey)),
+      );
+      final String adaptiveString = theme.getAdaptation<String>()!.adapt(theme, 'Default theme');
+      final SwitchThemeData adaptiveSwitchTheme = theme.getAdaptation<SwitchThemeData>()!
+        .adapt(theme, theme.switchTheme);
+
+      expect(adaptiveString, 'Adaptive theme.');
+      expect(adaptiveSwitchTheme.thumbColor?.resolve(<MaterialState>{}),
+        isSameColorAs(Colors.brown));
+    });
+
+    testWidgetsWithLeakTracking('should return null on extension not found', (WidgetTester tester) async {
+      final ThemeData theme = ThemeData(
+        adaptations: const <Adaptation<Object>>[
+          StringAdaptation(),
+        ],
+      );
+
+      expect(theme.extension<SwitchThemeAdaptation>(), isNull);
+    });
+  });
+
   testWidgetsWithLeakTracking(
     'ThemeData.brightness not matching ColorScheme.brightness throws a helpful error message', (WidgetTester tester) async {
-      AssertionError? error;
-
-      // Test `ColorScheme.light()` and `ThemeData.brightness == Brightness.dark`.
-      try {
-        await tester.pumpWidget(
-          MaterialApp(
-            theme: ThemeData(
-              colorScheme: const ColorScheme.light(),
-              brightness: Brightness.dark,
-            ),
-            home: const Placeholder(),
+    AssertionError? error;
+
+    // Test `ColorScheme.light()` and `ThemeData.brightness == Brightness.dark`.
+    try {
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: ThemeData(
+            colorScheme: const ColorScheme.light(),
+            brightness: Brightness.dark,
           ),
-        );
-      } on AssertionError catch (e) {
-        error = e;
-      } finally {
-        expect(error, isNotNull);
-        expect(error?.message, contains(
-          'ThemeData.brightness does not match ColorScheme.brightness. '
+          home: const Placeholder(),
+        ),
+      );
+    } on AssertionError catch (e) {
+      error = e;
+    } finally {
+      expect(error, isNotNull);
+      expect(error?.message, contains(
+        'ThemeData.brightness does not match ColorScheme.brightness. '
           'Either override ColorScheme.brightness or ThemeData.brightness to '
           'match the other.'
-        ));
-      }
-
-      // Test `ColorScheme.dark()` and `ThemeData.brightness == Brightness.light`.
-      try {
-        await tester.pumpWidget(
-          MaterialApp(
-            theme: ThemeData(
-              colorScheme: const ColorScheme.dark(),
-              brightness: Brightness.light,
-            ),
-            home: const Placeholder(),
+      ));
+    }
+
+    // Test `ColorScheme.dark()` and `ThemeData.brightness == Brightness.light`.
+    try {
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: ThemeData(
+            colorScheme: const ColorScheme.dark(),
+            brightness: Brightness.light,
           ),
-        );
-      } on AssertionError catch (e) {
-        error = e;
-      } finally {
-        expect(error, isNotNull);
-        expect(error?.message, contains(
-          'ThemeData.brightness does not match ColorScheme.brightness. '
+          home: const Placeholder(),
+        ),
+      );
+    } on AssertionError catch (e) {
+      error = e;
+    } finally {
+      expect(error, isNotNull);
+      expect(error?.message, contains(
+        'ThemeData.brightness does not match ColorScheme.brightness. '
           'Either override ColorScheme.brightness or ThemeData.brightness to '
           'match the other.'
-        ));
-      }
-
-      // Test `ColorScheme.fromSeed()` and `ThemeData.brightness == Brightness.dark`.
-      try {
-        await tester.pumpWidget(
-          MaterialApp(
-            theme: ThemeData(
-              colorScheme: ColorScheme.fromSeed(seedColor: const Color(0xffff0000)),
-              brightness: Brightness.dark,
-            ),
-            home: const Placeholder(),
+      ));
+    }
+
+    // Test `ColorScheme.fromSeed()` and `ThemeData.brightness == Brightness.dark`.
+    try {
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: ThemeData(
+            colorScheme: ColorScheme.fromSeed(seedColor: const Color(0xffff0000)),
+            brightness: Brightness.dark,
           ),
-        );
-      } on AssertionError catch (e) {
-        error = e;
-      } finally {
-        expect(error, isNotNull);
-        expect(error?.message, contains(
-          'ThemeData.brightness does not match ColorScheme.brightness. '
+          home: const Placeholder(),
+        ),
+      );
+    } on AssertionError catch (e) {
+      error = e;
+    } finally {
+      expect(error, isNotNull);
+      expect(error?.message, contains(
+        'ThemeData.brightness does not match ColorScheme.brightness. '
           'Either override ColorScheme.brightness or ThemeData.brightness to '
           'match the other.'
-        ));
-      }
-
-      // Test `ColorScheme.fromSeed()` using `Brightness.dark` and `ThemeData.brightness == Brightness.light`.
-      try {
-        await tester.pumpWidget(
-          MaterialApp(
-            theme: ThemeData(
-              colorScheme: ColorScheme.fromSeed(
-                seedColor: const Color(0xffff0000),
-                brightness: Brightness.dark,
-              ),
-              brightness: Brightness.light,
+      ));
+    }
+
+    // Test `ColorScheme.fromSeed()` using `Brightness.dark` and `ThemeData.brightness == Brightness.light`.
+    try {
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: ThemeData(
+            colorScheme: ColorScheme.fromSeed(
+              seedColor: const Color(0xffff0000),
+              brightness: Brightness.dark,
             ),
-            home: const Placeholder(),
+            brightness: Brightness.light,
           ),
-        );
-      } on AssertionError catch (e) {
-        error = e;
-      } finally {
-        expect(error, isNotNull);
-        expect(error?.message, contains(
-          'ThemeData.brightness does not match ColorScheme.brightness. '
+          home: const Placeholder(),
+        ),
+      );
+    } on AssertionError catch (e) {
+      error = e;
+    } finally {
+      expect(error, isNotNull);
+      expect(error?.message, contains(
+        'ThemeData.brightness does not match ColorScheme.brightness. '
           'Either override ColorScheme.brightness or ThemeData.brightness to '
           'match the other.'
-        ));
-      }
+      ));
+    }
   });
 }
 
@@ -1437,3 +1483,19 @@ class MyThemeExtensionB extends ThemeExtension<MyThemeExtensionB> {
     );
   }
 }
+
+class SwitchThemeAdaptation extends Adaptation<SwitchThemeData> {
+  const SwitchThemeAdaptation();
+
+  @override
+  SwitchThemeData adapt(ThemeData theme, SwitchThemeData defaultValue) => const SwitchThemeData(
+    thumbColor: MaterialStatePropertyAll<Color>(Colors.brown),
+  );
+}
+
+class StringAdaptation extends Adaptation<String> {
+  const StringAdaptation();
+
+  @override
+  String adapt(ThemeData theme, String defaultValue) => 'Adaptive theme.';
+}