Adaptive Switch (flutter#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.

Author: QuncCccccc

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

@@ -0,0 +1,134 @@
+// 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

@@ -0,0 +1,63 @@
+// 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
+    );
+  });
+}