packages/flutter/lib/src/cupertino/switch.dart - mirrors/flutter - Git at Google

 // 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 'dart:ui' show lerpDouble;

 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter/services.dart';

 import 'colors.dart';
 import 'thumb_painter.dart';

 // Examples can assume:
 // bool _lights;
 // void setState(VoidCallback fn) { }

 /// An iOS-style switch.
 ///
 /// Used to toggle the on/off state of a single setting.
 ///
 /// The switch itself does not maintain any state. Instead, when the state of
 /// the switch changes, the widget calls the [onChanged] callback. Most widgets
 /// that use a switch will listen for the [onChanged] callback and rebuild the
 /// switch with a new [value] to update the visual appearance of the switch.
 ///
 /// {@tool snippet}
 ///
 /// This sample shows how to use a [CupertinoSwitch] in a [ListTile]. The
 /// [MergeSemantics] is used to turn the entire [ListTile] into a single item
 /// for accessibility tools.
 ///
 /// ```dart
 /// MergeSemantics(
 ///   child: ListTile(
 ///     title: Text('Lights'),
 ///     trailing: CupertinoSwitch(
 ///       value: _lights,
 ///       onChanged: (bool value) { setState(() { _lights = value; }); },
 ///     ),
 ///     onTap: () { setState(() { _lights = !_lights; }); },
 ///   ),
 /// )
 /// ```
 /// {@end-tool}
 ///
 /// See also:
 ///
 ///  * [Switch], the material design equivalent.
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/controls/switches/>
 class CupertinoSwitch extends StatefulWidget {
   /// Creates an iOS-style switch.
   ///
   /// The [value] parameter must not be null.
   /// The [dragStartBehavior] parameter defaults to [DragStartBehavior.start] and must not be null.
   const CupertinoSwitch({
     Key key,
     @required this.value,
     @required this.onChanged,
     this.activeColor,
     this.trackColor,
     this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(value != null),
        assert(dragStartBehavior != null),
        super(key: key);

   /// Whether this switch is on or off.
   ///
   /// Must not be null.
   final bool value;

   /// Called when the user toggles with switch on or off.
   ///
   /// The switch passes the new value to the callback but does not actually
   /// change state until the parent widget rebuilds the switch with the new
   /// value.
   ///
   /// If null, the switch will be displayed as disabled, which has a reduced opacity.
   ///
   /// The callback provided to onChanged should update the state of the parent
   /// [StatefulWidget] using the [State.setState] method, so that the parent
   /// gets rebuilt; for example:
   ///
   /// ```dart
   /// CupertinoSwitch(
   ///   value: _giveVerse,
   ///   onChanged: (bool newValue) {
   ///     setState(() {
   ///       _giveVerse = newValue;
   ///     });
   ///   },
   /// )
   /// ```
   final ValueChanged<bool> onChanged;

   /// The color to use when this switch is on.
   ///
   /// Defaults to [CupertinoColors.systemGreen] when null and ignores
   /// the [CupertinoTheme] in accordance to native iOS behavior.
   final Color activeColor;

   /// The color to use for the background when the switch is off.
   ///
   /// Defaults to [CupertinoColors.secondarySystemFill] when null.
   final Color trackColor;

   /// {@template flutter.cupertino.switch.dragStartBehavior}
   /// Determines the way that drag start behavior is handled.
   ///
   /// If set to [DragStartBehavior.start], the drag behavior used to move the
   /// switch from on to off will begin upon the detection of a drag gesture. If
   /// set to [DragStartBehavior.down] it will begin when a down event is first
   /// detected.
   ///
   /// In general, setting this to [DragStartBehavior.start] will make drag
   /// animation smoother and setting it to [DragStartBehavior.down] will make
   /// drag behavior feel slightly more reactive.
   ///
   /// By default, the drag start behavior is [DragStartBehavior.start].
   ///
   /// See also:
   ///
   ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for
   ///    the different behaviors.
   ///
   /// {@endtemplate}
   final DragStartBehavior dragStartBehavior;

   @override
   _CupertinoSwitchState createState() => _CupertinoSwitchState();

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
     properties.add(FlagProperty('value', value: value, ifTrue: 'on', ifFalse: 'off', showName: true));
     properties.add(ObjectFlagProperty<ValueChanged<bool>>('onChanged', onChanged, ifNull: 'disabled'));
   }
 }

 class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderStateMixin {
   TapGestureRecognizer _tap;
   HorizontalDragGestureRecognizer _drag;

   AnimationController _positionController;
   CurvedAnimation position;

   AnimationController _reactionController;
   Animation<double> _reaction;

   bool get isInteractive => widget.onChanged != null;

   // 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;

   @override
   void initState() {
     super.initState();

     _tap = TapGestureRecognizer()
       ..onTapDown = _handleTapDown
       ..onTapUp = _handleTapUp
       ..onTap = _handleTap
       ..onTapCancel = _handleTapCancel;
     _drag = HorizontalDragGestureRecognizer()
       ..onStart = _handleDragStart
       ..onUpdate = _handleDragUpdate
       ..onEnd = _handleDragEnd
       ..dragStartBehavior = widget.dragStartBehavior;

     _positionController = AnimationController(
       duration: _kToggleDuration,
       value: widget.value ? 1.0 : 0.0,
       vsync: this,
     );
     position = CurvedAnimation(
       parent: _positionController,
       curve: Curves.linear,
     );
     _reactionController = AnimationController(
       duration: _kReactionDuration,
       vsync: this,
     );
     _reaction = CurvedAnimation(
       parent: _reactionController,
       curve: Curves.ease,
     );
   }

   @override
   void didUpdateWidget(CupertinoSwitch oldWidget) {
     super.didUpdateWidget(oldWidget);
     _drag.dragStartBehavior = widget.dragStartBehavior;

     if (needsPositionAnimation || oldWidget.value != widget.value)
       _resumePositionAnimation(isLinear: needsPositionAnimation);
   }

   // `isLinear` must be true if the position animation is trying to move the
   // thumb to the closest end after the most recent drag animation, so the curve
   // does not change when the controller's value is not 0 or 1.
   //
   // It can be set to false when it's an implicit animation triggered by
   // widget.value changes.
   void _resumePositionAnimation({ bool isLinear = true }) {
     needsPositionAnimation = false;
     position
       ..curve = isLinear ? null : Curves.ease
       ..reverseCurve = isLinear ? null : Curves.ease.flipped;
     if (widget.value)
       _positionController.forward();
     else
       _positionController.reverse();
   }

   void _handleTapDown(TapDownDetails details) {
     if (isInteractive)
       needsPositionAnimation = false;
       _reactionController.forward();
   }

   void _handleTap() {
     if (isInteractive) {
       widget.onChanged(!widget.value);
       _emitVibration();
     }
   }

   void _handleTapUp(TapUpDetails details) {
     if (isInteractive) {
       needsPositionAnimation = false;
       _reactionController.reverse();
     }
   }

   void _handleTapCancel() {
     if (isInteractive)
       _reactionController.reverse();
   }

   void _handleDragStart(DragStartDetails details) {
     if (isInteractive) {
       needsPositionAnimation = false;
       _reactionController.forward();
       _emitVibration();
     }
   }

   void _handleDragUpdate(DragUpdateDetails details) {
     if (isInteractive) {
       position
         ..curve = null
         ..reverseCurve = null;
       final double delta = details.primaryDelta / _kTrackInnerLength;
       switch (Directionality.of(context)) {
         case TextDirection.rtl:
           _positionController.value -= delta;
           break;
         case TextDirection.ltr:
           _positionController.value += delta;
           break;
       }
     }
   }

   void _handleDragEnd(DragEndDetails details) {
     // Deferring the animation to the next build phase.
     setState(() { needsPositionAnimation = true; });
     // Call onChanged when the user's intent to change value is clear.
     if (position.value >= 0.5 != widget.value)
       widget.onChanged(!widget.value);
     _reactionController.reverse();
   }

   void _emitVibration() {
     switch (defaultTargetPlatform) {
       case TargetPlatform.iOS:
         HapticFeedback.lightImpact();
         break;
       case TargetPlatform.android:
       case TargetPlatform.fuchsia:
       case TargetPlatform.linux:
       case TargetPlatform.macOS:
       case TargetPlatform.windows:
         break;
     }
   }

   @override
   Widget build(BuildContext context) {
     if (needsPositionAnimation)
       _resumePositionAnimation();
     return Opacity(
       opacity: widget.onChanged == null ? _kCupertinoSwitchDisabledOpacity : 1.0,
       child: _CupertinoSwitchRenderObjectWidget(
         value: widget.value,
         activeColor: CupertinoDynamicColor.resolve(
           widget.activeColor ?? CupertinoColors.systemGreen,
           context,
         ),
         trackColor: CupertinoDynamicColor.resolve(widget.trackColor ?? CupertinoColors.secondarySystemFill, context),
         onChanged: widget.onChanged,
         textDirection: Directionality.of(context),
         state: this,
       ),
     );
   }

   @override
   void dispose() {
     _tap.dispose();
     _drag.dispose();

     _positionController.dispose();
     _reactionController.dispose();
     super.dispose();
   }
 }

 class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
   const _CupertinoSwitchRenderObjectWidget({
     Key key,
     this.value,
     this.activeColor,
     this.trackColor,
     this.onChanged,
     this.textDirection,
     this.state,
   }) : super(key: key);

   final bool value;
   final Color activeColor;
   final Color trackColor;
   final ValueChanged<bool> onChanged;
   final _CupertinoSwitchState state;
   final TextDirection textDirection;

   @override
   _RenderCupertinoSwitch createRenderObject(BuildContext context) {
     return _RenderCupertinoSwitch(
       value: value,
       activeColor: activeColor,
       trackColor: trackColor,
       onChanged: onChanged,
       textDirection: textDirection,
       state: state,
     );
   }

   @override
   void updateRenderObject(BuildContext context, _RenderCupertinoSwitch renderObject) {
     renderObject
       ..value = value
       ..activeColor = activeColor
       ..trackColor = trackColor
       ..onChanged = onChanged
       ..textDirection = textDirection;
   }
 }

 const double _kTrackWidth = 51.0;
 const double _kTrackHeight = 31.0;
 const double _kTrackRadius = _kTrackHeight / 2.0;
 const double _kTrackInnerStart = _kTrackHeight / 2.0;
 const double _kTrackInnerEnd = _kTrackWidth - _kTrackInnerStart;
 const double _kTrackInnerLength = _kTrackInnerEnd - _kTrackInnerStart;
 const double _kSwitchWidth = 59.0;
 const double _kSwitchHeight = 39.0;
 // Opacity of a disabled switch, as eye-balled from iOS Simulator on Mac.
 const double _kCupertinoSwitchDisabledOpacity = 0.5;

 const Duration _kReactionDuration = Duration(milliseconds: 300);
 const Duration _kToggleDuration = Duration(milliseconds: 200);

 class _RenderCupertinoSwitch extends RenderConstrainedBox {
   _RenderCupertinoSwitch({
     @required bool value,
     @required Color activeColor,
     @required Color trackColor,
     ValueChanged<bool> onChanged,
     @required TextDirection textDirection,
     @required _CupertinoSwitchState state,
   }) : assert(value != null),
        assert(activeColor != null),
        assert(state != null),
        _value = value,
        _activeColor = activeColor,
        _trackColor = trackColor,
        _onChanged = onChanged,
        _textDirection = textDirection,
        _state = state,
        super(additionalConstraints: const BoxConstraints.tightFor(width: _kSwitchWidth, height: _kSwitchHeight)) {
          state.position.addListener(markNeedsPaint);
          state._reaction.addListener(markNeedsPaint);
   }

   final _CupertinoSwitchState _state;

   bool get value => _value;
   bool _value;
   set value(bool value) {
     assert(value != null);
     if (value == _value)
       return;
     _value = value;
     markNeedsSemanticsUpdate();
   }

   Color get activeColor => _activeColor;
   Color _activeColor;
   set activeColor(Color value) {
     assert(value != null);
     if (value == _activeColor)
       return;
     _activeColor = value;
     markNeedsPaint();
   }

   Color get trackColor => _trackColor;
   Color _trackColor;
   set trackColor(Color value) {
     assert(value != null);
     if (value == _trackColor)
       return;
     _trackColor = value;
     markNeedsPaint();
   }

   ValueChanged<bool> get onChanged => _onChanged;
   ValueChanged<bool> _onChanged;
   set onChanged(ValueChanged<bool> value) {
     if (value == _onChanged)
       return;
     final bool wasInteractive = isInteractive;
     _onChanged = value;
     if (wasInteractive != isInteractive) {
       markNeedsPaint();
       markNeedsSemanticsUpdate();
     }
   }

   TextDirection get textDirection => _textDirection;
   TextDirection _textDirection;
   set textDirection(TextDirection value) {
     assert(value != null);
     if (_textDirection == value)
       return;
     _textDirection = value;
     markNeedsPaint();
   }

   bool get isInteractive => onChanged != null;

   @override
   bool hitTestSelf(Offset position) => true;

   @override
   void handleEvent(PointerEvent event, BoxHitTestEntry entry) {
     assert(debugHandleEvent(event, entry));
     if (event is PointerDownEvent && isInteractive) {
       _state._drag.addPointer(event);
       _state._tap.addPointer(event);
     }
   }

   @override
   void describeSemanticsConfiguration(SemanticsConfiguration config) {
     super.describeSemanticsConfiguration(config);

     if (isInteractive)
       config.onTap = _state._handleTap;

     config.isEnabled = isInteractive;
     config.isToggled = _value;
   }

   @override
   void paint(PaintingContext context, Offset offset) {
     final Canvas canvas = context.canvas;

     final double currentValue = _state.position.value;
     final double currentReactionValue = _state._reaction.value;

     double visualPosition;
     switch (textDirection) {
       case TextDirection.rtl:
         visualPosition = 1.0 - currentValue;
         break;
       case TextDirection.ltr:
         visualPosition = currentValue;
         break;
     }

     final Paint paint = Paint()
       ..color = Color.lerp(trackColor, activeColor, currentValue);

     final Rect trackRect = Rect.fromLTWH(
         offset.dx + (size.width - _kTrackWidth) / 2.0,
         offset.dy + (size.height - _kTrackHeight) / 2.0,
         _kTrackWidth,
         _kTrackHeight,
     );
     final RRect trackRRect = RRect.fromRectAndRadius(trackRect, const Radius.circular(_kTrackRadius));
     canvas.drawRRect(trackRRect, paint);

     final double currentThumbExtension = CupertinoThumbPainter.extension * currentReactionValue;
     final double thumbLeft = lerpDouble(
       trackRect.left + _kTrackInnerStart - CupertinoThumbPainter.radius,
       trackRect.left + _kTrackInnerEnd - CupertinoThumbPainter.radius - currentThumbExtension,
       visualPosition,
     );
     final double thumbRight = lerpDouble(
       trackRect.left + _kTrackInnerStart + CupertinoThumbPainter.radius + currentThumbExtension,
       trackRect.left + _kTrackInnerEnd + CupertinoThumbPainter.radius,
       visualPosition,
     );
     final double thumbCenterY = offset.dy + size.height / 2.0;
     final Rect thumbBounds = Rect.fromLTRB(
       thumbLeft,
       thumbCenterY - CupertinoThumbPainter.radius,
       thumbRight,
       thumbCenterY + CupertinoThumbPainter.radius,
     );

     context.pushClipRRect(needsCompositing, Offset.zero, thumbBounds, trackRRect, (PaintingContext innerContext, Offset offset) {
       const CupertinoThumbPainter.switchThumb().paint(innerContext.canvas, thumbBounds);
     });
   }

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder description) {
     super.debugFillProperties(description);
     description.add(FlagProperty('value', value: value, ifTrue: 'checked', ifFalse: 'unchecked', showName: true));
     description.add(FlagProperty('isInteractive', value: isInteractive, ifTrue: 'enabled', ifFalse: 'disabled', showName: true, defaultValue: true));
   }
 }
	// 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 'dart:ui' show lerpDouble;

	import 'package:flutter/foundation.dart';
	import 'package:flutter/gestures.dart';
	import 'package:flutter/rendering.dart';
	import 'package:flutter/widgets.dart';
	import 'package:flutter/services.dart';

	import 'colors.dart';
	import 'thumb_painter.dart';

	// Examples can assume:
	// bool _lights;
	// void setState(VoidCallback fn) { }

	/// An iOS-style switch.
	///
	/// Used to toggle the on/off state of a single setting.
	///
	/// The switch itself does not maintain any state. Instead, when the state of
	/// the switch changes, the widget calls the [onChanged] callback. Most widgets
	/// that use a switch will listen for the [onChanged] callback and rebuild the
	/// switch with a new [value] to update the visual appearance of the switch.
	///
	/// {@tool snippet}
	///
	/// This sample shows how to use a [CupertinoSwitch] in a [ListTile]. The
	/// [MergeSemantics] is used to turn the entire [ListTile] into a single item
	/// for accessibility tools.
	///
	/// ```dart
	/// MergeSemantics(
	/// child: ListTile(
	/// title: Text('Lights'),
	/// trailing: CupertinoSwitch(
	/// value: _lights,
	/// onChanged: (bool value) { setState(() { _lights = value; }); },
	/// ),
	/// onTap: () { setState(() { _lights = !_lights; }); },
	/// ),
	/// )
	/// ```
	/// {@end-tool}
	///
	/// See also:
	///
	/// * [Switch], the material design equivalent.
	/// * <https://developer.apple.com/ios/human-interface-guidelines/controls/switches/>
	class CupertinoSwitch extends StatefulWidget {
	/// Creates an iOS-style switch.
	///
	/// The [value] parameter must not be null.
	/// The [dragStartBehavior] parameter defaults to [DragStartBehavior.start] and must not be null.
	const CupertinoSwitch({
	Key key,
	@required this.value,
	@required this.onChanged,
	this.activeColor,
	this.trackColor,
	this.dragStartBehavior = DragStartBehavior.start,
	}) : assert(value != null),
	assert(dragStartBehavior != null),
	super(key: key);

	/// Whether this switch is on or off.
	///
	/// Must not be null.
	final bool value;

	/// Called when the user toggles with switch on or off.
	///
	/// The switch passes the new value to the callback but does not actually
	/// change state until the parent widget rebuilds the switch with the new
	/// value.
	///
	/// If null, the switch will be displayed as disabled, which has a reduced opacity.
	///
	/// The callback provided to onChanged should update the state of the parent
	/// [StatefulWidget] using the [State.setState] method, so that the parent
	/// gets rebuilt; for example:
	///
	/// ```dart
	/// CupertinoSwitch(
	/// value: _giveVerse,
	/// onChanged: (bool newValue) {
	/// setState(() {
	/// _giveVerse = newValue;
	/// });
	/// },
	/// )
	/// ```
	final ValueChanged<bool> onChanged;

	/// The color to use when this switch is on.
	///
	/// Defaults to [CupertinoColors.systemGreen] when null and ignores
	/// the [CupertinoTheme] in accordance to native iOS behavior.
	final Color activeColor;

	/// The color to use for the background when the switch is off.
	///
	/// Defaults to [CupertinoColors.secondarySystemFill] when null.
	final Color trackColor;

	/// {@template flutter.cupertino.switch.dragStartBehavior}
	/// Determines the way that drag start behavior is handled.
	///
	/// If set to [DragStartBehavior.start], the drag behavior used to move the
	/// switch from on to off will begin upon the detection of a drag gesture. If
	/// set to [DragStartBehavior.down] it will begin when a down event is first
	/// detected.
	///
	/// In general, setting this to [DragStartBehavior.start] will make drag
	/// animation smoother and setting it to [DragStartBehavior.down] will make
	/// drag behavior feel slightly more reactive.
	///
	/// By default, the drag start behavior is [DragStartBehavior.start].
	///
	/// See also:
	///
	/// * [DragGestureRecognizer.dragStartBehavior], which gives an example for
	/// the different behaviors.
	///
	/// {@endtemplate}
	final DragStartBehavior dragStartBehavior;

	@override
	_CupertinoSwitchState createState() => _CupertinoSwitchState();

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder properties) {
	super.debugFillProperties(properties);
	properties.add(FlagProperty('value', value: value, ifTrue: 'on', ifFalse: 'off', showName: true));
	properties.add(ObjectFlagProperty<ValueChanged<bool>>('onChanged', onChanged, ifNull: 'disabled'));
	}
	}

	class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderStateMixin {
	TapGestureRecognizer _tap;
	HorizontalDragGestureRecognizer _drag;

	AnimationController _positionController;
	CurvedAnimation position;

	AnimationController _reactionController;
	Animation<double> _reaction;

	bool get isInteractive => widget.onChanged != null;

	// 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;

	@override
	void initState() {
	super.initState();

	_tap = TapGestureRecognizer()
	..onTapDown = _handleTapDown
	..onTapUp = _handleTapUp
	..onTap = _handleTap
	..onTapCancel = _handleTapCancel;
	_drag = HorizontalDragGestureRecognizer()
	..onStart = _handleDragStart
	..onUpdate = _handleDragUpdate
	..onEnd = _handleDragEnd
	..dragStartBehavior = widget.dragStartBehavior;

	_positionController = AnimationController(
	duration: _kToggleDuration,
	value: widget.value ? 1.0 : 0.0,
	vsync: this,
	);
	position = CurvedAnimation(
	parent: _positionController,
	curve: Curves.linear,
	);
	_reactionController = AnimationController(
	duration: _kReactionDuration,
	vsync: this,
	);
	_reaction = CurvedAnimation(
	parent: _reactionController,
	curve: Curves.ease,
	);
	}

	@override
	void didUpdateWidget(CupertinoSwitch oldWidget) {
	super.didUpdateWidget(oldWidget);
	_drag.dragStartBehavior = widget.dragStartBehavior;

	if (needsPositionAnimation \|\| oldWidget.value != widget.value)
	_resumePositionAnimation(isLinear: needsPositionAnimation);
	}

	// `isLinear` must be true if the position animation is trying to move the
	// thumb to the closest end after the most recent drag animation, so the curve
	// does not change when the controller's value is not 0 or 1.
	//
	// It can be set to false when it's an implicit animation triggered by
	// widget.value changes.
	void _resumePositionAnimation({ bool isLinear = true }) {
	needsPositionAnimation = false;
	position
	..curve = isLinear ? null : Curves.ease
	..reverseCurve = isLinear ? null : Curves.ease.flipped;
	if (widget.value)
	_positionController.forward();
	else
	_positionController.reverse();
	}

	void _handleTapDown(TapDownDetails details) {
	if (isInteractive)
	needsPositionAnimation = false;
	_reactionController.forward();
	}

	void _handleTap() {
	if (isInteractive) {
	widget.onChanged(!widget.value);
	_emitVibration();
	}
	}

	void _handleTapUp(TapUpDetails details) {
	if (isInteractive) {
	needsPositionAnimation = false;
	_reactionController.reverse();
	}
	}

	void _handleTapCancel() {
	if (isInteractive)
	_reactionController.reverse();
	}

	void _handleDragStart(DragStartDetails details) {
	if (isInteractive) {
	needsPositionAnimation = false;
	_reactionController.forward();
	_emitVibration();
	}
	}

	void _handleDragUpdate(DragUpdateDetails details) {
	if (isInteractive) {
	position
	..curve = null
	..reverseCurve = null;
	final double delta = details.primaryDelta / _kTrackInnerLength;
	switch (Directionality.of(context)) {
	case TextDirection.rtl:
	_positionController.value -= delta;
	break;
	case TextDirection.ltr:
	_positionController.value += delta;
	break;
	}
	}
	}

	void _handleDragEnd(DragEndDetails details) {
	// Deferring the animation to the next build phase.
	setState(() { needsPositionAnimation = true; });
	// Call onChanged when the user's intent to change value is clear.
	if (position.value >= 0.5 != widget.value)
	widget.onChanged(!widget.value);
	_reactionController.reverse();
	}

	void _emitVibration() {
	switch (defaultTargetPlatform) {
	case TargetPlatform.iOS:
	HapticFeedback.lightImpact();
	break;
	case TargetPlatform.android:
	case TargetPlatform.fuchsia:
	case TargetPlatform.linux:
	case TargetPlatform.macOS:
	case TargetPlatform.windows:
	break;
	}
	}

	@override
	Widget build(BuildContext context) {
	if (needsPositionAnimation)
	_resumePositionAnimation();
	return Opacity(
	opacity: widget.onChanged == null ? _kCupertinoSwitchDisabledOpacity : 1.0,
	child: _CupertinoSwitchRenderObjectWidget(
	value: widget.value,
	activeColor: CupertinoDynamicColor.resolve(
	widget.activeColor ?? CupertinoColors.systemGreen,
	context,
	),
	trackColor: CupertinoDynamicColor.resolve(widget.trackColor ?? CupertinoColors.secondarySystemFill, context),
	onChanged: widget.onChanged,
	textDirection: Directionality.of(context),
	state: this,
	),
	);
	}

	@override
	void dispose() {
	_tap.dispose();
	_drag.dispose();

	_positionController.dispose();
	_reactionController.dispose();
	super.dispose();
	}
	}

	class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
	const _CupertinoSwitchRenderObjectWidget({
	Key key,
	this.value,
	this.activeColor,
	this.trackColor,
	this.onChanged,
	this.textDirection,
	this.state,
	}) : super(key: key);

	final bool value;
	final Color activeColor;
	final Color trackColor;
	final ValueChanged<bool> onChanged;
	final _CupertinoSwitchState state;
	final TextDirection textDirection;

	@override
	_RenderCupertinoSwitch createRenderObject(BuildContext context) {
	return _RenderCupertinoSwitch(
	value: value,
	activeColor: activeColor,
	trackColor: trackColor,
	onChanged: onChanged,
	textDirection: textDirection,
	state: state,
	);
	}

	@override
	void updateRenderObject(BuildContext context, _RenderCupertinoSwitch renderObject) {
	renderObject
	..value = value
	..activeColor = activeColor
	..trackColor = trackColor
	..onChanged = onChanged
	..textDirection = textDirection;
	}
	}

	const double _kTrackWidth = 51.0;
	const double _kTrackHeight = 31.0;
	const double _kTrackRadius = _kTrackHeight / 2.0;
	const double _kTrackInnerStart = _kTrackHeight / 2.0;
	const double _kTrackInnerEnd = _kTrackWidth - _kTrackInnerStart;
	const double _kTrackInnerLength = _kTrackInnerEnd - _kTrackInnerStart;
	const double _kSwitchWidth = 59.0;
	const double _kSwitchHeight = 39.0;
	// Opacity of a disabled switch, as eye-balled from iOS Simulator on Mac.
	const double _kCupertinoSwitchDisabledOpacity = 0.5;

	const Duration _kReactionDuration = Duration(milliseconds: 300);
	const Duration _kToggleDuration = Duration(milliseconds: 200);

	class _RenderCupertinoSwitch extends RenderConstrainedBox {
	_RenderCupertinoSwitch({
	@required bool value,
	@required Color activeColor,
	@required Color trackColor,
	ValueChanged<bool> onChanged,
	@required TextDirection textDirection,
	@required _CupertinoSwitchState state,
	}) : assert(value != null),
	assert(activeColor != null),
	assert(state != null),
	_value = value,
	_activeColor = activeColor,
	_trackColor = trackColor,
	_onChanged = onChanged,
	_textDirection = textDirection,
	_state = state,
	super(additionalConstraints: const BoxConstraints.tightFor(width: _kSwitchWidth, height: _kSwitchHeight)) {
	state.position.addListener(markNeedsPaint);
	state._reaction.addListener(markNeedsPaint);
	}

	final _CupertinoSwitchState _state;

	bool get value => _value;
	bool _value;
	set value(bool value) {
	assert(value != null);
	if (value == _value)
	return;
	_value = value;
	markNeedsSemanticsUpdate();
	}

	Color get activeColor => _activeColor;
	Color _activeColor;
	set activeColor(Color value) {
	assert(value != null);
	if (value == _activeColor)
	return;
	_activeColor = value;
	markNeedsPaint();
	}

	Color get trackColor => _trackColor;
	Color _trackColor;
	set trackColor(Color value) {
	assert(value != null);
	if (value == _trackColor)
	return;
	_trackColor = value;
	markNeedsPaint();
	}

	ValueChanged<bool> get onChanged => _onChanged;
	ValueChanged<bool> _onChanged;
	set onChanged(ValueChanged<bool> value) {
	if (value == _onChanged)
	return;
	final bool wasInteractive = isInteractive;
	_onChanged = value;
	if (wasInteractive != isInteractive) {
	markNeedsPaint();
	markNeedsSemanticsUpdate();
	}
	}

	TextDirection get textDirection => _textDirection;
	TextDirection _textDirection;
	set textDirection(TextDirection value) {
	assert(value != null);
	if (_textDirection == value)
	return;
	_textDirection = value;
	markNeedsPaint();
	}

	bool get isInteractive => onChanged != null;

	@override
	bool hitTestSelf(Offset position) => true;

	@override
	void handleEvent(PointerEvent event, BoxHitTestEntry entry) {
	assert(debugHandleEvent(event, entry));
	if (event is PointerDownEvent && isInteractive) {
	_state._drag.addPointer(event);
	_state._tap.addPointer(event);
	}
	}

	@override
	void describeSemanticsConfiguration(SemanticsConfiguration config) {
	super.describeSemanticsConfiguration(config);

	if (isInteractive)
	config.onTap = _state._handleTap;

	config.isEnabled = isInteractive;
	config.isToggled = _value;
	}

	@override
	void paint(PaintingContext context, Offset offset) {
	final Canvas canvas = context.canvas;

	final double currentValue = _state.position.value;
	final double currentReactionValue = _state._reaction.value;

	double visualPosition;
	switch (textDirection) {
	case TextDirection.rtl:
	visualPosition = 1.0 - currentValue;
	break;
	case TextDirection.ltr:
	visualPosition = currentValue;
	break;
	}

	final Paint paint = Paint()
	..color = Color.lerp(trackColor, activeColor, currentValue);

	final Rect trackRect = Rect.fromLTWH(
	offset.dx + (size.width - _kTrackWidth) / 2.0,
	offset.dy + (size.height - _kTrackHeight) / 2.0,
	_kTrackWidth,
	_kTrackHeight,
	);
	final RRect trackRRect = RRect.fromRectAndRadius(trackRect, const Radius.circular(_kTrackRadius));
	canvas.drawRRect(trackRRect, paint);

	final double currentThumbExtension = CupertinoThumbPainter.extension * currentReactionValue;
	final double thumbLeft = lerpDouble(
	trackRect.left + _kTrackInnerStart - CupertinoThumbPainter.radius,
	trackRect.left + _kTrackInnerEnd - CupertinoThumbPainter.radius - currentThumbExtension,
	visualPosition,
	);
	final double thumbRight = lerpDouble(
	trackRect.left + _kTrackInnerStart + CupertinoThumbPainter.radius + currentThumbExtension,
	trackRect.left + _kTrackInnerEnd + CupertinoThumbPainter.radius,
	visualPosition,
	);
	final double thumbCenterY = offset.dy + size.height / 2.0;
	final Rect thumbBounds = Rect.fromLTRB(
	thumbLeft,
	thumbCenterY - CupertinoThumbPainter.radius,
	thumbRight,
	thumbCenterY + CupertinoThumbPainter.radius,
	);

	context.pushClipRRect(needsCompositing, Offset.zero, thumbBounds, trackRRect, (PaintingContext innerContext, Offset offset) {
	const CupertinoThumbPainter.switchThumb().paint(innerContext.canvas, thumbBounds);
	});
	}

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder description) {
	super.debugFillProperties(description);
	description.add(FlagProperty('value', value: value, ifTrue: 'checked', ifFalse: 'unchecked', showName: true));
	description.add(FlagProperty('isInteractive', value: isInteractive, ifTrue: 'enabled', ifFalse: 'disabled', showName: true, defaultValue: true));
	}
	}