Add focus detector to CupertinoSwitch (#118345)

* Add focus detector to CupertinoSwitch

* Add comment

* Remove whitespace

* Add focusColor constructor to CupertinoSwitch

* Remove whitespace

* Add color type

* Remove gap in border

* Adjust color and line thickness

dev/benchmarks/complex_layout/windows/flutter/generated_plugins.cmake

+#
+# Generated file, do not edit.
+#
+
+list(APPEND FLUTTER_PLUGIN_LIST
+)
+
+list(APPEND FLUTTER_FFI_PLUGIN_LIST
+)
+
+set(PLUGIN_BUNDLED_LIBRARIES)
+
+foreach(plugin ${FLUTTER_PLUGIN_LIST})
+  add_subdirectory(flutter/ephemeral/.plugin_symlinks/${plugin}/windows plugins/${plugin})
+  target_link_libraries(${BINARY_NAME} PRIVATE ${plugin}_plugin)
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES $<TARGET_FILE:${plugin}_plugin>)
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES ${${plugin}_bundled_libraries})
+endforeach(plugin)
+
+foreach(ffi_plugin ${FLUTTER_FFI_PLUGIN_LIST})
+  add_subdirectory(flutter/ephemeral/.plugin_symlinks/${ffi_plugin}/windows plugins/${ffi_plugin})
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES ${${ffi_plugin}_bundled_libraries})
+endforeach(ffi_plugin)

examples/flutter_view/windows/flutter/generated_plugins.cmake

+#
+# Generated file, do not edit.
+#
+
+list(APPEND FLUTTER_PLUGIN_LIST
+)
+
+list(APPEND FLUTTER_FFI_PLUGIN_LIST
+)
+
+set(PLUGIN_BUNDLED_LIBRARIES)
+
+foreach(plugin ${FLUTTER_PLUGIN_LIST})
+  add_subdirectory(flutter/ephemeral/.plugin_symlinks/${plugin}/windows plugins/${plugin})
+  target_link_libraries(${BINARY_NAME} PRIVATE ${plugin}_plugin)
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES $<TARGET_FILE:${plugin}_plugin>)
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES ${${plugin}_bundled_libraries})
+endforeach(plugin)
+
+foreach(ffi_plugin ${FLUTTER_FFI_PLUGIN_LIST})
+  add_subdirectory(flutter/ephemeral/.plugin_symlinks/${ffi_plugin}/windows plugins/${ffi_plugin})
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES ${${ffi_plugin}_bundled_libraries})
+endforeach(ffi_plugin)

examples/platform_view/windows/flutter/generated_plugins.cmake

+#
+# Generated file, do not edit.
+#
+
+list(APPEND FLUTTER_PLUGIN_LIST
+)
+
+list(APPEND FLUTTER_FFI_PLUGIN_LIST
+)
+
+set(PLUGIN_BUNDLED_LIBRARIES)
+
+foreach(plugin ${FLUTTER_PLUGIN_LIST})
+  add_subdirectory(flutter/ephemeral/.plugin_symlinks/${plugin}/windows plugins/${plugin})
+  target_link_libraries(${BINARY_NAME} PRIVATE ${plugin}_plugin)
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES $<TARGET_FILE:${plugin}_plugin>)
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES ${${plugin}_bundled_libraries})
+endforeach(plugin)
+
+foreach(ffi_plugin ${FLUTTER_FFI_PLUGIN_LIST})
+  add_subdirectory(flutter/ephemeral/.plugin_symlinks/${ffi_plugin}/windows plugins/${ffi_plugin})
+  list(APPEND PLUGIN_BUNDLED_LIBRARIES ${${ffi_plugin}_bundled_libraries})
+endforeach(ffi_plugin)

packages/flutter/lib/src/cupertino/switch.dart

@@ -74,6 +74,7 @@ class CupertinoSwitch extends StatefulWidget {
     this.trackColor,
     this.thumbColor,
     this.applyTheme,
+    this.focusColor,
     this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(value != null),
        assert(dragStartBehavior != null);
@@ -125,6 +126,11 @@ class CupertinoSwitch extends StatefulWidget {
   /// Defaults to [CupertinoColors.white] when null.
   final Color? thumbColor;
 
+  /// The color to use for the focus highlight for keyboard interactions.
+  ///
+  /// Defaults to a a slightly transparent [activeColor].
+  final Color? focusColor;
+
   /// {@template flutter.cupertino.CupertinoSwitch.applyTheme}
   /// Whether to apply the ambient [CupertinoThemeData].
   ///
@@ -178,8 +184,14 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
   late AnimationController _reactionController;
   late Animation<double> _reaction;
 
+  late bool isFocused;
+
   bool get isInteractive => widget.onChanged != null;
 
+  late final Map<Type, Action<Intent>> _actionMap = <Type, Action<Intent>>{
+    ActivateIntent: CallbackAction<ActivateIntent>(onInvoke: _handleTap),
+  };
+
   // A non-null boolean value that changes to true at the end of a drag if the
   // switch must be animated to the position indicated by the widget's value.
   bool needsPositionAnimation = false;
@@ -188,6 +200,8 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
   void initState() {
     super.initState();
 
+    isFocused = false;
+
     _tap = TapGestureRecognizer()
       ..onTapDown = _handleTapDown
       ..onTapUp = _handleTapUp
@@ -253,7 +267,7 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
       _reactionController.forward();
   }
 
-  void _handleTap() {
+  void _handleTap([Intent? _]) {
     if (isInteractive) {
       widget.onChanged!(!widget.value);
       _emitVibration();
@@ -322,9 +336,19 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
     }
   }
 
+  void _onShowFocusHighlight(bool showHighlight) {
+    setState(() { isFocused = showHighlight; });
+  }
+
   @override
   Widget build(BuildContext context) {
     final CupertinoThemeData theme = CupertinoTheme.of(context);
+    final Color activeColor = CupertinoDynamicColor.resolve(
+      widget.activeColor
+      ?? ((widget.applyTheme ?? theme.applyThemeToAll) ? theme.primaryColor : null)
+      ?? CupertinoColors.systemGreen,
+      context,
+    );
     if (needsPositionAnimation) {
       _resumePositionAnimation();
     }
@@ -332,21 +356,31 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
       cursor: isInteractive && kIsWeb ? SystemMouseCursors.click : MouseCursor.defer,
       child: Opacity(
         opacity: widget.onChanged == null ? _kCupertinoSwitchDisabledOpacity : 1.0,
+        child: FocusableActionDetector(
+          onShowFocusHighlight: _onShowFocusHighlight,
+          actions: _actionMap,
+          enabled: isInteractive,
           child: _CupertinoSwitchRenderObjectWidget(
             value: widget.value,
-          activeColor: CupertinoDynamicColor.resolve(
-            widget.activeColor
-            ?? ((widget.applyTheme ?? theme.applyThemeToAll) ? theme.primaryColor : null)
-            ?? CupertinoColors.systemGreen,
-            context,
-          ),
+            activeColor: activeColor,
             trackColor: CupertinoDynamicColor.resolve(widget.trackColor ?? CupertinoColors.secondarySystemFill, context),
             thumbColor: CupertinoDynamicColor.resolve(widget.thumbColor ?? CupertinoColors.white, context),
+            // Opacity, lightness, and saturation values were aproximated with
+            // color pickers on the switches in the macOS settings.
+            focusColor: CupertinoDynamicColor.resolve(
+              widget.focusColor ??
+              HSLColor
+                    .fromColor(activeColor.withOpacity(0.80))
+                    .withLightness(0.69).withSaturation(0.835)
+                    .toColor(),
+              context),
             onChanged: widget.onChanged,
             textDirection: Directionality.of(context),
+            isFocused: isFocused,
             state: this,
           ),
         ),
+      ),
     );
   }
 
@@ -367,8 +401,10 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
     required this.activeColor,
     required this.trackColor,
     required this.thumbColor,
+    required this.focusColor,
     required this.onChanged,
     required this.textDirection,
+    required this.isFocused,
     required this.state,
   });
 
@@ -376,9 +412,11 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
   final Color activeColor;
   final Color trackColor;
   final Color thumbColor;
+  final Color focusColor;
   final ValueChanged<bool>? onChanged;
   final _CupertinoSwitchState state;
   final TextDirection textDirection;
+  final bool isFocused;
 
   @override
   _RenderCupertinoSwitch createRenderObject(BuildContext context) {
@@ -387,8 +425,10 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
       activeColor: activeColor,
       trackColor: trackColor,
       thumbColor: thumbColor,
+      focusColor: focusColor,
       onChanged: onChanged,
       textDirection: textDirection,
+      isFocused: isFocused,
       state: state,
     );
   }
@@ -401,8 +441,10 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
       ..activeColor = activeColor
       ..trackColor = trackColor
       ..thumbColor = thumbColor
+      ..focusColor = focusColor
       ..onChanged = onChanged
-      ..textDirection = textDirection;
+      ..textDirection = textDirection
+      ..isFocused = isFocused;
   }
 }
 
@@ -426,8 +468,10 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     required Color activeColor,
     required Color trackColor,
     required Color thumbColor,
+    required Color focusColor,
     ValueChanged<bool>? onChanged,
     required TextDirection textDirection,
+    required bool isFocused,
     required _CupertinoSwitchState state,
   }) : assert(value != null),
        assert(activeColor != null),
@@ -435,9 +479,11 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
        _value = value,
        _activeColor = activeColor,
        _trackColor = trackColor,
+       _focusColor = focusColor,
        _thumbPainter = CupertinoThumbPainter.switchThumb(color: thumbColor),
        _onChanged = onChanged,
        _textDirection = textDirection,
+       _isFocused = isFocused,
        _state = state,
        super(additionalConstraints: const BoxConstraints.tightFor(width: _kSwitchWidth, height: _kSwitchHeight)) {
          state.position.addListener(markNeedsPaint);
@@ -490,6 +536,17 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     markNeedsPaint();
   }
 
+  Color get focusColor => _focusColor;
+  Color _focusColor;
+  set focusColor(Color value) {
+    assert(value != null);
+    if (value == _focusColor) {
+      return;
+    }
+    _focusColor = value;
+    markNeedsPaint();
+  }
+
   ValueChanged<bool>? get onChanged => _onChanged;
   ValueChanged<bool>? _onChanged;
   set onChanged(ValueChanged<bool>? value) {
@@ -515,6 +572,17 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     markNeedsPaint();
   }
 
+  bool get isFocused => _isFocused;
+  bool _isFocused;
+  set isFocused(bool value) {
+    assert(value != null);
+    if(value == _isFocused) {
+      return;
+    }
+    _isFocused = value;
+    markNeedsPaint();
+  }
+
   bool get isInteractive => onChanged != null;
 
   @override
@@ -570,6 +638,18 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     final RRect trackRRect = RRect.fromRectAndRadius(trackRect, const Radius.circular(_kTrackRadius));
     canvas.drawRRect(trackRRect, paint);
 
+    if(_isFocused) {
+      // Paints a border around the switch in the focus color.
+      final RRect borderTrackRRect = trackRRect.inflate(1.75);
+
+      final Paint borderPaint = Paint()
+        ..color = focusColor
+        ..style = PaintingStyle.stroke
+        ..strokeWidth = 3.5;
+
+      canvas.drawRRect(borderTrackRRect, borderPaint);
+    }
+
     final double currentThumbExtension = CupertinoThumbPainter.extension * currentReactionValue;
     final double thumbLeft = lerpDouble(
       trackRect.left + _kTrackInnerStart - CupertinoThumbPainter.radius,

packages/flutter/test/cupertino/switch_test.dart

@@ -48,6 +48,39 @@ void main() {
     expect(value, isTrue);
   });
 
+  testWidgets('CupertinoSwitch can be toggled by keyboard shortcuts', (WidgetTester tester) async {
+    bool value = true;
+    Widget buildApp({bool enabled = true}) {
+      return CupertinoApp(
+        home: CupertinoPageScaffold(
+          child: Center(
+            child: StatefulBuilder(builder: (BuildContext context, StateSetter setState) {
+              return CupertinoSwitch(
+                value: value,
+                onChanged: enabled ? (bool newValue) {
+                  setState(() {
+                    value = newValue;
+                  });
+                } : null,
+              );
+            }),
+          ),
+        ),
+      );
+    }
+    await tester.pumpWidget(buildApp());
+    await tester.pumpAndSettle();
+    expect(value, isTrue);
+    await tester.sendKeyEvent(LogicalKeyboardKey.tab);
+    await tester.pumpAndSettle();
+    await tester.sendKeyEvent(LogicalKeyboardKey.space);
+    await tester.pumpAndSettle();
+    expect(value, isFalse);
+    await tester.sendKeyEvent(LogicalKeyboardKey.space);
+    await tester.pumpAndSettle();
+    expect(value, isTrue);
+  });
+
   testWidgets('Switch emits light haptic vibration on tap', (WidgetTester tester) async {
     final Key switchKey = UniqueKey();
     bool value = false;