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

 // Copyright 2015 The Chromium 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/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';

 import 'colors.dart';
 import 'constants.dart';
 import 'debug.dart';
 import 'shadows.dart';
 import 'theme.dart';
 import 'toggleable.dart';

 /// A material design 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.
 ///
 /// Requires one of its ancestors to be a [Material] widget.
 ///
 /// See also:
 ///
 ///  * [SwitchListTile], which combines this widget with a [ListTile] so that
 ///    you can give the switch a label.
 ///  * [Checkbox], another widget with similar semantics.
 ///  * [Radio], for selecting among a set of explicit values.
 ///  * [Slider], for selecting a value in a range.
 ///  * <https://material.google.com/components/selection-controls.html#selection-controls-switch>
 class Switch extends StatefulWidget {
   /// Creates a material design switch.
   ///
   /// 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.
   ///
   /// The following arguments are required:
   ///
   /// * [value] determines whether this switch is on or off.
   /// * [onChanged] is called when the user toggles the switch on or off.
   const Switch({
     Key key,
     @required this.value,
     @required this.onChanged,
     this.activeColor,
     this.activeTrackColor,
     this.inactiveThumbColor,
     this.inactiveTrackColor,
     this.activeThumbImage,
     this.inactiveThumbImage
   }) : super(key: key);

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

   /// Called when the user toggles the 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.
   ///
   /// 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
   /// new Switch(
   ///   value: _giveVerse,
   ///   onChanged: (bool newValue) {
   ///     setState(() {
   ///       _giveVerse = newValue;
   ///     });
   ///   },
   /// )
   /// ```
   final ValueChanged<bool> onChanged;

   /// The color to use when this switch is on.
   ///
   /// Defaults to [ThemeData.toggleableActiveColor].
   final Color activeColor;

   /// The color to use on the track when this switch is on.
   ///
   /// Defaults to [ThemeData.toggleableActiveColor] with the opacity set at 50%.
   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.
   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.
   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.
   final ImageProvider inactiveThumbImage;

   @override
   _SwitchState createState() => new _SwitchState();

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

 class _SwitchState extends State<Switch> with TickerProviderStateMixin {
   @override
   Widget build(BuildContext context) {
     assert(debugCheckHasMaterial(context));
     final ThemeData themeData = Theme.of(context);
     final bool isDark = themeData.brightness == Brightness.dark;

     final Color activeThumbColor = widget.activeColor ?? themeData.toggleableActiveColor;
     final Color activeTrackColor = widget.activeTrackColor ?? activeThumbColor.withAlpha(0x80);

     Color inactiveThumbColor;
     Color inactiveTrackColor;
     if (widget.onChanged != null) {
       inactiveThumbColor = widget.inactiveThumbColor ?? (isDark ? Colors.grey.shade400 : Colors.grey.shade50);
       inactiveTrackColor = widget.inactiveTrackColor ?? (isDark ? Colors.white30 : Colors.black26);
     } else {
       inactiveThumbColor = widget.inactiveThumbColor ?? (isDark ? Colors.grey.shade800 : Colors.grey.shade400);
       inactiveTrackColor = widget.inactiveTrackColor ?? (isDark ? Colors.white10 : Colors.black12);
     }

     return new _SwitchRenderObjectWidget(
       value: widget.value,
       activeColor: activeThumbColor,
       inactiveColor: inactiveThumbColor,
       activeThumbImage: widget.activeThumbImage,
       inactiveThumbImage: widget.inactiveThumbImage,
       activeTrackColor: activeTrackColor,
       inactiveTrackColor: inactiveTrackColor,
       configuration: createLocalImageConfiguration(context),
       onChanged: widget.onChanged,
       vsync: this,
     );
   }
 }

 class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
   const _SwitchRenderObjectWidget({
     Key key,
     this.value,
     this.activeColor,
     this.inactiveColor,
     this.activeThumbImage,
     this.inactiveThumbImage,
     this.activeTrackColor,
     this.inactiveTrackColor,
     this.configuration,
     this.onChanged,
     this.vsync,
   }) : super(key: key);

   final bool value;
   final Color activeColor;
   final Color inactiveColor;
   final ImageProvider activeThumbImage;
   final ImageProvider inactiveThumbImage;
   final Color activeTrackColor;
   final Color inactiveTrackColor;
   final ImageConfiguration configuration;
   final ValueChanged<bool> onChanged;
   final TickerProvider vsync;

   @override
   _RenderSwitch createRenderObject(BuildContext context) {
     return new _RenderSwitch(
       value: value,
       activeColor: activeColor,
       inactiveColor: inactiveColor,
       activeThumbImage: activeThumbImage,
       inactiveThumbImage: inactiveThumbImage,
       activeTrackColor: activeTrackColor,
       inactiveTrackColor: inactiveTrackColor,
       configuration: configuration,
       onChanged: onChanged,
       textDirection: Directionality.of(context),
       vsync: vsync,
     );
   }

   @override
   void updateRenderObject(BuildContext context, _RenderSwitch renderObject) {
     renderObject
       ..value = value
       ..activeColor = activeColor
       ..inactiveColor = inactiveColor
       ..activeThumbImage = activeThumbImage
       ..inactiveThumbImage = inactiveThumbImage
       ..activeTrackColor = activeTrackColor
       ..inactiveTrackColor = inactiveTrackColor
       ..configuration = configuration
       ..onChanged = onChanged
       ..textDirection = Directionality.of(context)
       ..vsync = vsync;
   }
 }

 const double _kTrackHeight = 14.0;
 const double _kTrackWidth = 33.0;
 const double _kTrackRadius = _kTrackHeight / 2.0;
 const double _kThumbRadius = 10.0;
 const double _kSwitchWidth = _kTrackWidth - 2 * _kTrackRadius + 2 * kRadialReactionRadius;
 const double _kSwitchHeight = 2 * kRadialReactionRadius;

 class _RenderSwitch extends RenderToggleable {
   _RenderSwitch({
     bool value,
     Color activeColor,
     Color inactiveColor,
     ImageProvider activeThumbImage,
     ImageProvider inactiveThumbImage,
     Color activeTrackColor,
     Color inactiveTrackColor,
     ImageConfiguration configuration,
     @required TextDirection textDirection,
     ValueChanged<bool> onChanged,
     @required TickerProvider vsync,
   }) : assert(textDirection != null),
        _activeThumbImage = activeThumbImage,
        _inactiveThumbImage = inactiveThumbImage,
        _activeTrackColor = activeTrackColor,
        _inactiveTrackColor = inactiveTrackColor,
        _configuration = configuration,
        _textDirection = textDirection,
        super(
          value: value,
          tristate: false,
          activeColor: activeColor,
          inactiveColor: inactiveColor,
          onChanged: onChanged,
          size: const Size(_kSwitchWidth, _kSwitchHeight),
          vsync: vsync,
        ) {
     _drag = new HorizontalDragGestureRecognizer()
       ..onStart = _handleDragStart
       ..onUpdate = _handleDragUpdate
       ..onEnd = _handleDragEnd;
   }

   ImageProvider get activeThumbImage => _activeThumbImage;
   ImageProvider _activeThumbImage;
   set activeThumbImage(ImageProvider value) {
     if (value == _activeThumbImage)
       return;
     _activeThumbImage = value;
     markNeedsPaint();
   }

   ImageProvider get inactiveThumbImage => _inactiveThumbImage;
   ImageProvider _inactiveThumbImage;
   set inactiveThumbImage(ImageProvider value) {
     if (value == _inactiveThumbImage)
       return;
     _inactiveThumbImage = value;
     markNeedsPaint();
   }

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

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

   ImageConfiguration get configuration => _configuration;
   ImageConfiguration _configuration;
   set configuration(ImageConfiguration value) {
     assert(value != null);
     if (value == _configuration)
       return;
     _configuration = value;
     markNeedsPaint();
   }

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

   @override
   void detach() {
     _cachedThumbPainter?.dispose();
     _cachedThumbPainter = null;
     super.detach();
   }

   double get _trackInnerLength => size.width - 2.0 * kRadialReactionRadius;

   HorizontalDragGestureRecognizer _drag;

   void _handleDragStart(DragStartDetails details) {
     if (isInteractive)
       reactionController.forward();
   }

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

   void _handleDragEnd(DragEndDetails details) {
     if (position.value >= 0.5)
       positionController.forward();
     else
       positionController.reverse();
     reactionController.reverse();
   }

   @override
   void handleEvent(PointerEvent event, BoxHitTestEntry entry) {
     assert(debugHandleEvent(event, entry));
     if (event is PointerDownEvent && onChanged != null)
       _drag.addPointer(event);
     super.handleEvent(event, entry);
   }

   Color _cachedThumbColor;
   ImageProvider _cachedThumbImage;
   BoxPainter _cachedThumbPainter;

   BoxDecoration _createDefaultThumbDecoration(Color color, ImageProvider image) {
     return new BoxDecoration(
       color: color,
       image: image == null ? null : new DecorationImage(image: image),
       shape: BoxShape.circle,
       boxShadow: kElevationToShadow[1]
     );
   }

   bool _isPainting = false;

   void _handleDecorationChanged() {
     // If the image decoration is available synchronously, we'll get called here
     // during paint. There's no reason to mark ourselves as needing paint if we
     // are already in the middle of painting. (In fact, doing so would trigger
     // an assert).
     if (!_isPainting)
       markNeedsPaint();
   }

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

     final bool isActive = onChanged != null;
     final double currentValue = position.value;

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

     final Color trackColor = isActive ? Color.lerp(inactiveTrackColor, activeTrackColor, currentValue) : inactiveTrackColor;

     // Paint the track
     final Paint paint = new Paint()
       ..color = trackColor;
     const double trackHorizontalPadding = kRadialReactionRadius - _kTrackRadius;
     final Rect trackRect = new Rect.fromLTWH(
       offset.dx + trackHorizontalPadding,
       offset.dy + (size.height - _kTrackHeight) / 2.0,
       size.width - 2.0 * trackHorizontalPadding,
       _kTrackHeight
     );
     final RRect trackRRect = new RRect.fromRectAndRadius(trackRect, const Radius.circular(_kTrackRadius));
     canvas.drawRRect(trackRRect, paint);

     final Offset thumbPosition = new Offset(
       kRadialReactionRadius + visualPosition * _trackInnerLength,
       size.height / 2.0
     );

     paintRadialReaction(canvas, offset, thumbPosition);

     try {
       _isPainting = true;
       BoxPainter thumbPainter;
       final Color thumbColor = isActive ? Color.lerp(inactiveColor, activeColor, currentValue) : inactiveColor;
       final ImageProvider thumbImage = isActive ? (currentValue < 0.5 ? inactiveThumbImage : activeThumbImage) : inactiveThumbImage;
       if (_cachedThumbPainter == null || thumbColor != _cachedThumbColor || thumbImage != _cachedThumbImage) {
         _cachedThumbColor = thumbColor;
         _cachedThumbImage = thumbImage;
         _cachedThumbPainter = _createDefaultThumbDecoration(thumbColor, thumbImage).createBoxPainter(_handleDecorationChanged);
       }
       thumbPainter = _cachedThumbPainter;

       // The thumb contracts slightly during the animation
       final double inset = 1.0 - (currentValue - 0.5).abs() * 2.0;
       final double radius = _kThumbRadius - inset;
       thumbPainter.paint(
         canvas,
         thumbPosition + offset - new Offset(radius, radius),
         configuration.copyWith(size: new Size.fromRadius(radius))
       );
     } finally {
       _isPainting = false;
     }
   }
 }
	// Copyright 2015 The Chromium 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/foundation.dart';
	import 'package:flutter/gestures.dart';
	import 'package:flutter/rendering.dart';
	import 'package:flutter/widgets.dart';

	import 'colors.dart';
	import 'constants.dart';
	import 'debug.dart';
	import 'shadows.dart';
	import 'theme.dart';
	import 'toggleable.dart';

	/// A material design 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.
	///
	/// Requires one of its ancestors to be a [Material] widget.
	///
	/// See also:
	///
	/// * [SwitchListTile], which combines this widget with a [ListTile] so that
	/// you can give the switch a label.
	/// * [Checkbox], another widget with similar semantics.
	/// * [Radio], for selecting among a set of explicit values.
	/// * [Slider], for selecting a value in a range.
	/// * <https://material.google.com/components/selection-controls.html#selection-controls-switch>
	class Switch extends StatefulWidget {
	/// Creates a material design switch.
	///
	/// 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.
	///
	/// The following arguments are required:
	///
	/// * [value] determines whether this switch is on or off.
	/// * [onChanged] is called when the user toggles the switch on or off.
	const Switch({
	Key key,
	@required this.value,
	@required this.onChanged,
	this.activeColor,
	this.activeTrackColor,
	this.inactiveThumbColor,
	this.inactiveTrackColor,
	this.activeThumbImage,
	this.inactiveThumbImage
	}) : super(key: key);

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

	/// Called when the user toggles the 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.
	///
	/// 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
	/// new Switch(
	/// value: _giveVerse,
	/// onChanged: (bool newValue) {
	/// setState(() {
	/// _giveVerse = newValue;
	/// });
	/// },
	/// )
	/// ```
	final ValueChanged<bool> onChanged;

	/// The color to use when this switch is on.
	///
	/// Defaults to [ThemeData.toggleableActiveColor].
	final Color activeColor;

	/// The color to use on the track when this switch is on.
	///
	/// Defaults to [ThemeData.toggleableActiveColor] with the opacity set at 50%.
	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.
	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.
	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.
	final ImageProvider inactiveThumbImage;

	@override
	_SwitchState createState() => new _SwitchState();

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

	class _SwitchState extends State<Switch> with TickerProviderStateMixin {
	@override
	Widget build(BuildContext context) {
	assert(debugCheckHasMaterial(context));
	final ThemeData themeData = Theme.of(context);
	final bool isDark = themeData.brightness == Brightness.dark;

	final Color activeThumbColor = widget.activeColor ?? themeData.toggleableActiveColor;
	final Color activeTrackColor = widget.activeTrackColor ?? activeThumbColor.withAlpha(0x80);

	Color inactiveThumbColor;
	Color inactiveTrackColor;
	if (widget.onChanged != null) {
	inactiveThumbColor = widget.inactiveThumbColor ?? (isDark ? Colors.grey.shade400 : Colors.grey.shade50);
	inactiveTrackColor = widget.inactiveTrackColor ?? (isDark ? Colors.white30 : Colors.black26);
	} else {
	inactiveThumbColor = widget.inactiveThumbColor ?? (isDark ? Colors.grey.shade800 : Colors.grey.shade400);
	inactiveTrackColor = widget.inactiveTrackColor ?? (isDark ? Colors.white10 : Colors.black12);
	}

	return new _SwitchRenderObjectWidget(
	value: widget.value,
	activeColor: activeThumbColor,
	inactiveColor: inactiveThumbColor,
	activeThumbImage: widget.activeThumbImage,
	inactiveThumbImage: widget.inactiveThumbImage,
	activeTrackColor: activeTrackColor,
	inactiveTrackColor: inactiveTrackColor,
	configuration: createLocalImageConfiguration(context),
	onChanged: widget.onChanged,
	vsync: this,
	);
	}
	}

	class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
	const _SwitchRenderObjectWidget({
	Key key,
	this.value,
	this.activeColor,
	this.inactiveColor,
	this.activeThumbImage,
	this.inactiveThumbImage,
	this.activeTrackColor,
	this.inactiveTrackColor,
	this.configuration,
	this.onChanged,
	this.vsync,
	}) : super(key: key);

	final bool value;
	final Color activeColor;
	final Color inactiveColor;
	final ImageProvider activeThumbImage;
	final ImageProvider inactiveThumbImage;
	final Color activeTrackColor;
	final Color inactiveTrackColor;
	final ImageConfiguration configuration;
	final ValueChanged<bool> onChanged;
	final TickerProvider vsync;

	@override
	_RenderSwitch createRenderObject(BuildContext context) {
	return new _RenderSwitch(
	value: value,
	activeColor: activeColor,
	inactiveColor: inactiveColor,
	activeThumbImage: activeThumbImage,
	inactiveThumbImage: inactiveThumbImage,
	activeTrackColor: activeTrackColor,
	inactiveTrackColor: inactiveTrackColor,
	configuration: configuration,
	onChanged: onChanged,
	textDirection: Directionality.of(context),
	vsync: vsync,
	);
	}

	@override
	void updateRenderObject(BuildContext context, _RenderSwitch renderObject) {
	renderObject
	..value = value
	..activeColor = activeColor
	..inactiveColor = inactiveColor
	..activeThumbImage = activeThumbImage
	..inactiveThumbImage = inactiveThumbImage
	..activeTrackColor = activeTrackColor
	..inactiveTrackColor = inactiveTrackColor
	..configuration = configuration
	..onChanged = onChanged
	..textDirection = Directionality.of(context)
	..vsync = vsync;
	}
	}

	const double _kTrackHeight = 14.0;
	const double _kTrackWidth = 33.0;
	const double _kTrackRadius = _kTrackHeight / 2.0;
	const double _kThumbRadius = 10.0;
	const double _kSwitchWidth = _kTrackWidth - 2 * _kTrackRadius + 2 * kRadialReactionRadius;
	const double _kSwitchHeight = 2 * kRadialReactionRadius;

	class _RenderSwitch extends RenderToggleable {
	_RenderSwitch({
	bool value,
	Color activeColor,
	Color inactiveColor,
	ImageProvider activeThumbImage,
	ImageProvider inactiveThumbImage,
	Color activeTrackColor,
	Color inactiveTrackColor,
	ImageConfiguration configuration,
	@required TextDirection textDirection,
	ValueChanged<bool> onChanged,
	@required TickerProvider vsync,
	}) : assert(textDirection != null),
	_activeThumbImage = activeThumbImage,
	_inactiveThumbImage = inactiveThumbImage,
	_activeTrackColor = activeTrackColor,
	_inactiveTrackColor = inactiveTrackColor,
	_configuration = configuration,
	_textDirection = textDirection,
	super(
	value: value,
	tristate: false,
	activeColor: activeColor,
	inactiveColor: inactiveColor,
	onChanged: onChanged,
	size: const Size(_kSwitchWidth, _kSwitchHeight),
	vsync: vsync,
	) {
	_drag = new HorizontalDragGestureRecognizer()
	..onStart = _handleDragStart
	..onUpdate = _handleDragUpdate
	..onEnd = _handleDragEnd;
	}

	ImageProvider get activeThumbImage => _activeThumbImage;
	ImageProvider _activeThumbImage;
	set activeThumbImage(ImageProvider value) {
	if (value == _activeThumbImage)
	return;
	_activeThumbImage = value;
	markNeedsPaint();
	}

	ImageProvider get inactiveThumbImage => _inactiveThumbImage;
	ImageProvider _inactiveThumbImage;
	set inactiveThumbImage(ImageProvider value) {
	if (value == _inactiveThumbImage)
	return;
	_inactiveThumbImage = value;
	markNeedsPaint();
	}

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

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

	ImageConfiguration get configuration => _configuration;
	ImageConfiguration _configuration;
	set configuration(ImageConfiguration value) {
	assert(value != null);
	if (value == _configuration)
	return;
	_configuration = value;
	markNeedsPaint();
	}

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

	@override
	void detach() {
	_cachedThumbPainter?.dispose();
	_cachedThumbPainter = null;
	super.detach();
	}

	double get _trackInnerLength => size.width - 2.0 * kRadialReactionRadius;

	HorizontalDragGestureRecognizer _drag;

	void _handleDragStart(DragStartDetails details) {
	if (isInteractive)
	reactionController.forward();
	}

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

	void _handleDragEnd(DragEndDetails details) {
	if (position.value >= 0.5)
	positionController.forward();
	else
	positionController.reverse();
	reactionController.reverse();
	}

	@override
	void handleEvent(PointerEvent event, BoxHitTestEntry entry) {
	assert(debugHandleEvent(event, entry));
	if (event is PointerDownEvent && onChanged != null)
	_drag.addPointer(event);
	super.handleEvent(event, entry);
	}

	Color _cachedThumbColor;
	ImageProvider _cachedThumbImage;
	BoxPainter _cachedThumbPainter;

	BoxDecoration _createDefaultThumbDecoration(Color color, ImageProvider image) {
	return new BoxDecoration(
	color: color,
	image: image == null ? null : new DecorationImage(image: image),
	shape: BoxShape.circle,
	boxShadow: kElevationToShadow[1]
	);
	}

	bool _isPainting = false;

	void _handleDecorationChanged() {
	// If the image decoration is available synchronously, we'll get called here
	// during paint. There's no reason to mark ourselves as needing paint if we
	// are already in the middle of painting. (In fact, doing so would trigger
	// an assert).
	if (!_isPainting)
	markNeedsPaint();
	}

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

	final bool isActive = onChanged != null;
	final double currentValue = position.value;

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

	final Color trackColor = isActive ? Color.lerp(inactiveTrackColor, activeTrackColor, currentValue) : inactiveTrackColor;

	// Paint the track
	final Paint paint = new Paint()
	..color = trackColor;
	const double trackHorizontalPadding = kRadialReactionRadius - _kTrackRadius;
	final Rect trackRect = new Rect.fromLTWH(
	offset.dx + trackHorizontalPadding,
	offset.dy + (size.height - _kTrackHeight) / 2.0,
	size.width - 2.0 * trackHorizontalPadding,
	_kTrackHeight
	);
	final RRect trackRRect = new RRect.fromRectAndRadius(trackRect, const Radius.circular(_kTrackRadius));
	canvas.drawRRect(trackRRect, paint);

	final Offset thumbPosition = new Offset(
	kRadialReactionRadius + visualPosition * _trackInnerLength,
	size.height / 2.0
	);

	paintRadialReaction(canvas, offset, thumbPosition);

	try {
	_isPainting = true;
	BoxPainter thumbPainter;
	final Color thumbColor = isActive ? Color.lerp(inactiveColor, activeColor, currentValue) : inactiveColor;
	final ImageProvider thumbImage = isActive ? (currentValue < 0.5 ? inactiveThumbImage : activeThumbImage) : inactiveThumbImage;
	if (_cachedThumbPainter == null \|\| thumbColor != _cachedThumbColor \|\| thumbImage != _cachedThumbImage) {
	_cachedThumbColor = thumbColor;
	_cachedThumbImage = thumbImage;
	_cachedThumbPainter = _createDefaultThumbDecoration(thumbColor, thumbImage).createBoxPainter(_handleDecorationChanged);
	}
	thumbPainter = _cachedThumbPainter;

	// The thumb contracts slightly during the animation
	final double inset = 1.0 - (currentValue - 0.5).abs() * 2.0;
	final double radius = _kThumbRadius - inset;
	thumbPainter.paint(
	canvas,
	thumbPosition + offset - new Offset(radius, radius),
	configuration.copyWith(size: new Size.fromRadius(radius))
	);
	} finally {
	_isPainting = false;
	}
	}
	}