Switch list tile adaptive (#24437)

* SwitchListTile.adaptive for wrapping an adaptive Switch

* Test SwitchListTile.adaptive same as Switch.adaptive

* Remove TODO

* Comment and switch statement cleanup

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

@@ -13,6 +13,8 @@ import 'theme_data.dart';
 // void setState(VoidCallback fn) { }
 // bool _lights;
 
+enum _SwitchListTileType { material, adaptive }
+
 /// A [ListTile] with a [Switch]. In other words, a switch with a label.
 ///
 /// The entire list tile is interactive: tapping anywhere in the tile toggles
@@ -90,7 +92,39 @@ class SwitchListTile extends StatelessWidget {
     this.dense,
     this.secondary,
     this.selected = false,
-  }) : assert(value != null),
+  }) : _switchListTileType = _SwitchListTileType.material,
+       assert(value != null),
+       assert(isThreeLine != null),
+       assert(!isThreeLine || subtitle != null),
+       assert(selected != null),
+       super(key: key);
+
+  /// Creates the wrapped switch with [Switch.adaptive].
+  ///
+  /// Creates a [CupertinoSwitch] if the target platform is iOS, creates a
+  /// material design switch otherwise.
+  ///
+  /// If a [CupertinoSwitch] is created, the following parameters are
+  /// ignored: [activeTrackColor], [inactiveThumbColor], [inactiveTrackColor],
+  /// [activeThumbImage], [inactiveThumbImage], [materialTapTargetSize].
+  const SwitchListTile.adaptive({
+    Key key,
+    @required this.value,
+    @required this.onChanged,
+    this.activeColor,
+    this.activeTrackColor,
+    this.inactiveThumbColor,
+    this.inactiveTrackColor,
+    this.activeThumbImage,
+    this.inactiveThumbImage,
+    this.title,
+    this.subtitle,
+    this.isThreeLine = false,
+    this.dense,
+    this.secondary,
+    this.selected = false,
+  }) : _switchListTileType = _SwitchListTileType.adaptive,
+       assert(value != null),
        assert(isThreeLine != null),
        assert(!isThreeLine || subtitle != null),
        assert(selected != null),
@@ -134,22 +168,30 @@ class SwitchListTile extends StatelessWidget {
   /// The color to use on the track when this switch is on.
   ///
   /// Defaults to [ThemeData.toggleableActiveColor] with the opacity set at 50%.
+  ///
+  /// Ignored if created with [SwitchListTile.adaptive].
   final Color activeTrackColor;
 
   /// The color to use on the thumb when this switch is off.
   ///
   /// Defaults to the colors described in the Material design specification.
+  ///
+  /// Ignored if created with [SwitchListTile.adaptive].
   final Color inactiveThumbColor;
 
   /// The color to use on the track when this switch is off.
   ///
   /// Defaults to the colors described in the Material design specification.
+  ///
+  /// Ignored if created with [SwitchListTile.adaptive].
   final Color inactiveTrackColor;
 
   /// An image to use on the thumb of this switch when the switch is on.
   final ImageProvider activeThumbImage;
 
   /// An image to use on the thumb of this switch when the switch is off.
+  ///
+  /// Ignored if created with [SwitchListTile.adaptive].
   final ImageProvider inactiveThumbImage;
 
   /// The primary content of the list tile.
@@ -187,19 +229,40 @@ class SwitchListTile extends StatelessWidget {
   /// Normally, this property is left to its default value, false.
   final bool selected;
 
+  /// If adaptive, creates the switch with [Switch.adaptive].
+  final _SwitchListTileType _switchListTileType;
+
   @override
   Widget build(BuildContext context) {
-    final Widget control = Switch(
-      value: value,
-      onChanged: onChanged,
-      activeColor: activeColor,
-      activeThumbImage: activeThumbImage,
-      inactiveThumbImage: inactiveThumbImage,
-      materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
-      activeTrackColor: activeTrackColor,
-      inactiveTrackColor: inactiveTrackColor,
-      inactiveThumbColor: inactiveThumbColor,
-    );
+    Widget control;
+    switch (_switchListTileType) {
+      case _SwitchListTileType.adaptive:
+        control = Switch.adaptive(
+          value: value,
+          onChanged: onChanged,
+          activeColor: activeColor,
+          activeThumbImage: activeThumbImage,
+          inactiveThumbImage: inactiveThumbImage,
+          materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
+          activeTrackColor: activeTrackColor,
+          inactiveTrackColor: inactiveTrackColor,
+          inactiveThumbColor: inactiveThumbColor,
+        );
+        break;
+
+      case _SwitchListTileType.material:
+        control = Switch(
+          value: value,
+          onChanged: onChanged,
+          activeColor: activeColor,
+          activeThumbImage: activeThumbImage,
+          inactiveThumbImage: inactiveThumbImage,
+          materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
+          activeTrackColor: activeTrackColor,
+          inactiveTrackColor: inactiveTrackColor,
+          inactiveThumbColor: inactiveThumbColor,
+        );
+    }
     return MergeSemantics(
       child: ListTileTheme.merge(
         selectedColor: activeColor ?? Theme.of(context).accentColor,

packages/flutter/test/material/switch_list_tile_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import '../rendering/mock_canvas.dart';
@@ -58,4 +59,45 @@ void main() {
         ..circle(color: Colors.red[500])
     );
   });
+
+  testWidgets('SwitchListTile.adaptive delegates to', (WidgetTester tester) async {
+    bool value = false;
+
+     Widget buildFrame(TargetPlatform platform) {
+      return MaterialApp(
+        theme: ThemeData(platform: platform),
+        home: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setState) {
+            return Material(
+              child: Center(
+                child: SwitchListTile.adaptive(
+                  value: value,
+                  onChanged: (bool newValue) {
+                    setState(() {
+                      value = newValue;
+                    });
+                  },
+                ),
+              ),
+            );
+          },
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(TargetPlatform.iOS));
+    expect(find.byType(CupertinoSwitch), findsOneWidget);
+    expect(value, isFalse);
+
+    await tester.tap(find.byType(SwitchListTile));
+    expect(value, isTrue);
+
+    await tester.pumpWidget(buildFrame(TargetPlatform.android));
+    await tester.pumpAndSettle(); // Finish the theme change animation.
+
+    expect(find.byType(CupertinoSwitch), findsNothing);
+    expect(value, isTrue);
+    await tester.tap(find.byType(SwitchListTile));
+    expect(value, isFalse);
+  });
 }