packages/flutter/lib/src/cupertino/slider.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:math' as math;
 import 'dart:ui' show lerpDouble;

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

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

 // Examples can assume:
 // int _cupertinoSliderValue = 1;
 // void setState(VoidCallback fn) { }

 /// An iOS-style slider.
 ///
 /// Used to select from a range of values.
 ///
 /// A slider can be used to select from either a continuous or a discrete set of
 /// values. The default is use a continuous range of values from [min] to [max].
 /// To use discrete values, use a non-null value for [divisions], which
 /// indicates the number of discrete intervals. For example, if [min] is 0.0 and
 /// [max] is 50.0 and [divisions] is 5, then the slider can take on the values
 /// discrete values 0.0, 10.0, 20.0, 30.0, 40.0, and 50.0.
 ///
 /// The slider itself does not maintain any state. Instead, when the state of
 /// the slider changes, the widget calls the [onChanged] callback. Most widgets
 /// that use a slider will listen for the [onChanged] callback and rebuild the
 /// slider with a new [value] to update the visual appearance of the slider.
 ///
 /// See also:
 ///
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/controls/sliders/>
 class CupertinoSlider extends StatefulWidget {
   /// Creates an iOS-style slider.
   ///
   /// The slider itself does not maintain any state. Instead, when the state of
   /// the slider changes, the widget calls the [onChanged] callback. Most widgets
   /// that use a slider will listen for the [onChanged] callback and rebuild the
   /// slider with a new [value] to update the visual appearance of the slider.
   ///
   /// * [value] determines currently selected value for this slider.
   /// * [onChanged] is called when the user selects a new value for the slider.
   /// * [onChangeStart] is called when the user starts to select a new value for
   ///   the slider.
   /// * [onChangeEnd] is called when the user is done selecting a new value for
   ///   the slider.
   const CupertinoSlider({
     Key key,
     @required this.value,
     @required this.onChanged,
     this.onChangeStart,
     this.onChangeEnd,
     this.min = 0.0,
     this.max = 1.0,
     this.divisions,
     this.activeColor,
     this.thumbColor = CupertinoColors.white,
   }) : assert(value != null),
        assert(min != null),
        assert(max != null),
        assert(value >= min && value <= max),
        assert(divisions == null || divisions > 0),
        assert(thumbColor != null),
        super(key: key);

   /// The currently selected value for this slider.
   ///
   /// The slider's thumb is drawn at a position that corresponds to this value.
   final double value;

   /// Called when the user selects a new value for the slider.
   ///
   /// The slider passes the new value to the callback but does not actually
   /// change state until the parent widget rebuilds the slider with the new
   /// value.
   ///
   /// If null, the slider 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
   /// CupertinoSlider(
   ///   value: _cupertinoSliderValue.toDouble(),
   ///   min: 1.0,
   ///   max: 10.0,
   ///   divisions: 10,
   ///   onChanged: (double newValue) {
   ///     setState(() {
   ///       _cupertinoSliderValue = newValue.round();
   ///     });
   ///   },
   /// )
   /// ```
   ///
   /// See also:
   ///
   ///  * [onChangeStart] for a callback that is called when the user starts
   ///    changing the value.
   ///  * [onChangeEnd] for a callback that is called when the user stops
   ///    changing the value.
   final ValueChanged<double> onChanged;

   /// Called when the user starts selecting a new value for the slider.
   ///
   /// This callback shouldn't be used to update the slider [value] (use
   /// [onChanged] for that), but rather to be notified when the user has started
   /// selecting a new value by starting a drag.
   ///
   /// The value passed will be the last [value] that the slider had before the
   /// change began.
   ///
   /// {@tool snippet}
   ///
   /// ```dart
   /// CupertinoSlider(
   ///   value: _cupertinoSliderValue.toDouble(),
   ///   min: 1.0,
   ///   max: 10.0,
   ///   divisions: 10,
   ///   onChanged: (double newValue) {
   ///     setState(() {
   ///       _cupertinoSliderValue = newValue.round();
   ///     });
   ///   },
   ///   onChangeStart: (double startValue) {
   ///     print('Started change at $startValue');
   ///   },
   /// )
   /// ```
   /// {@end-tool}
   ///
   /// See also:
   ///
   ///  * [onChangeEnd] for a callback that is called when the value change is
   ///    complete.
   final ValueChanged<double> onChangeStart;

   /// Called when the user is done selecting a new value for the slider.
   ///
   /// This callback shouldn't be used to update the slider [value] (use
   /// [onChanged] for that), but rather to know when the user has completed
   /// selecting a new [value] by ending a drag.
   ///
   /// {@tool snippet}
   ///
   /// ```dart
   /// CupertinoSlider(
   ///   value: _cupertinoSliderValue.toDouble(),
   ///   min: 1.0,
   ///   max: 10.0,
   ///   divisions: 10,
   ///   onChanged: (double newValue) {
   ///     setState(() {
   ///       _cupertinoSliderValue = newValue.round();
   ///     });
   ///   },
   ///   onChangeEnd: (double newValue) {
   ///     print('Ended change on $newValue');
   ///   },
   /// )
   /// ```
   /// {@end-tool}
   ///
   /// See also:
   ///
   ///  * [onChangeStart] for a callback that is called when a value change
   ///    begins.
   final ValueChanged<double> onChangeEnd;

   /// The minimum value the user can select.
   ///
   /// Defaults to 0.0.
   final double min;

   /// The maximum value the user can select.
   ///
   /// Defaults to 1.0.
   final double max;

   /// The number of discrete divisions.
   ///
   /// If null, the slider is continuous.
   final int divisions;

   /// The color to use for the portion of the slider that has been selected.
   ///
   /// Defaults to the [CupertinoTheme]'s primary color if null.
   final Color activeColor;

   /// The color to use for the thumb of the slider.
   ///
   /// Thumb color must not be null.
   ///
   /// Defaults to [CupertinoColors.white].
   final Color thumbColor;

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

   @override
   void debugFillProperties(DiagnosticPropertiesBuilder properties) {
     super.debugFillProperties(properties);
     properties.add(DoubleProperty('value', value));
     properties.add(DoubleProperty('min', min));
     properties.add(DoubleProperty('max', max));
   }
 }

 class _CupertinoSliderState extends State<CupertinoSlider> with TickerProviderStateMixin {
   void _handleChanged(double value) {
     assert(widget.onChanged != null);
     final double lerpValue = lerpDouble(widget.min, widget.max, value);
     if (lerpValue != widget.value) {
       widget.onChanged(lerpValue);
     }
   }

   void _handleDragStart(double value) {
     assert(widget.onChangeStart != null);
     widget.onChangeStart(lerpDouble(widget.min, widget.max, value));
   }

   void _handleDragEnd(double value) {
     assert(widget.onChangeEnd != null);
     widget.onChangeEnd(lerpDouble(widget.min, widget.max, value));
   }

   @override
   Widget build(BuildContext context) {
     return _CupertinoSliderRenderObjectWidget(
       value: (widget.value - widget.min) / (widget.max - widget.min),
       divisions: widget.divisions,
       activeColor: CupertinoDynamicColor.resolve(
         widget.activeColor ?? CupertinoTheme.of(context).primaryColor,
         context,
       ),
       thumbColor: widget.thumbColor,
       onChanged: widget.onChanged != null ? _handleChanged : null,
       onChangeStart: widget.onChangeStart != null ? _handleDragStart : null,
       onChangeEnd: widget.onChangeEnd != null ? _handleDragEnd : null,
       vsync: this,
     );
   }
 }

 class _CupertinoSliderRenderObjectWidget extends LeafRenderObjectWidget {
   const _CupertinoSliderRenderObjectWidget({
     Key key,
     this.value,
     this.divisions,
     this.activeColor,
     this.thumbColor,
     this.onChanged,
     this.onChangeStart,
     this.onChangeEnd,
     this.vsync,
   }) : super(key: key);

   final double value;
   final int divisions;
   final Color activeColor;
   final Color thumbColor;
   final ValueChanged<double> onChanged;
   final ValueChanged<double> onChangeStart;
   final ValueChanged<double> onChangeEnd;
   final TickerProvider vsync;

   @override
   _RenderCupertinoSlider createRenderObject(BuildContext context) {
     return _RenderCupertinoSlider(
       value: value,
       divisions: divisions,
       activeColor: activeColor,
       thumbColor: CupertinoDynamicColor.resolve(thumbColor, context),
       trackColor: CupertinoDynamicColor.resolve(CupertinoColors.systemFill, context),
       onChanged: onChanged,
       onChangeStart: onChangeStart,
       onChangeEnd: onChangeEnd,
       vsync: vsync,
       textDirection: Directionality.of(context),
     );
   }

   @override
   void updateRenderObject(BuildContext context, _RenderCupertinoSlider renderObject) {
     renderObject
       ..value = value
       ..divisions = divisions
       ..activeColor = activeColor
       ..thumbColor = CupertinoDynamicColor.resolve(thumbColor, context)
       ..trackColor = CupertinoDynamicColor.resolve(CupertinoColors.systemFill, context)
       ..onChanged = onChanged
       ..onChangeStart = onChangeStart
       ..onChangeEnd = onChangeEnd
       ..textDirection = Directionality.of(context);
     // Ticker provider cannot change since there's a 1:1 relationship between
     // the _SliderRenderObjectWidget object and the _SliderState object.
   }
 }

 const double _kPadding = 8.0;
 const double _kSliderHeight = 2.0 * (CupertinoThumbPainter.radius + _kPadding);
 const double _kSliderWidth = 176.0; // Matches Material Design slider.
 const Duration _kDiscreteTransitionDuration = Duration(milliseconds: 500);

 const double _kAdjustmentUnit = 0.1; // Matches iOS implementation of material slider.

 class _RenderCupertinoSlider extends RenderConstrainedBox {
   _RenderCupertinoSlider({
     @required double value,
     int divisions,
     Color activeColor,
     Color thumbColor,
     Color trackColor,
     ValueChanged<double> onChanged,
     this.onChangeStart,
     this.onChangeEnd,
     TickerProvider vsync,
     @required TextDirection textDirection,
   }) : assert(value != null && value >= 0.0 && value <= 1.0),
        assert(textDirection != null),
        _value = value,
        _divisions = divisions,
        _activeColor = activeColor,
        _thumbColor = thumbColor,
        _trackColor = trackColor,
        _onChanged = onChanged,
        _textDirection = textDirection,
        super(additionalConstraints: const BoxConstraints.tightFor(width: _kSliderWidth, height: _kSliderHeight)) {
     _drag = HorizontalDragGestureRecognizer()
       ..onStart = _handleDragStart
       ..onUpdate = _handleDragUpdate
       ..onEnd = _handleDragEnd;
     _position = AnimationController(
       value: value,
       duration: _kDiscreteTransitionDuration,
       vsync: vsync,
     )..addListener(markNeedsPaint);
   }

   double get value => _value;
   double _value;
   set value(double newValue) {
     assert(newValue != null && newValue >= 0.0 && newValue <= 1.0);
     if (newValue == _value)
       return;
     _value = newValue;
     if (divisions != null)
       _position.animateTo(newValue, curve: Curves.fastOutSlowIn);
     else
       _position.value = newValue;
     markNeedsSemanticsUpdate();
   }

   int get divisions => _divisions;
   int _divisions;
   set divisions(int value) {
     if (value == _divisions)
       return;
     _divisions = value;
     markNeedsPaint();
   }

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

   Color get thumbColor => _thumbColor;
   Color _thumbColor;
   set thumbColor(Color value) {
     if (value == _thumbColor)
       return;
     _thumbColor = value;
     markNeedsPaint();
   }

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

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

   ValueChanged<double> onChangeStart;
   ValueChanged<double> onChangeEnd;

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

   AnimationController _position;

   HorizontalDragGestureRecognizer _drag;
   double _currentDragValue = 0.0;

   double get _discretizedCurrentDragValue {
     double dragValue = _currentDragValue.clamp(0.0, 1.0) as double;
     if (divisions != null)
       dragValue = (dragValue * divisions).round() / divisions;
     return dragValue;
   }

   double get _trackLeft => _kPadding;
   double get _trackRight => size.width - _kPadding;
   double get _thumbCenter {
     double visualPosition;
     switch (textDirection) {
       case TextDirection.rtl:
         visualPosition = 1.0 - _value;
         break;
       case TextDirection.ltr:
         visualPosition = _value;
         break;
     }
     return lerpDouble(_trackLeft + CupertinoThumbPainter.radius, _trackRight - CupertinoThumbPainter.radius, visualPosition);
   }

   bool get isInteractive => onChanged != null;

   void _handleDragStart(DragStartDetails details) => _startInteraction(details.globalPosition);

   void _handleDragUpdate(DragUpdateDetails details) {
     if (isInteractive) {
       final double extent = math.max(_kPadding, size.width - 2.0 * (_kPadding + CupertinoThumbPainter.radius));
       final double valueDelta = details.primaryDelta / extent;
       switch (textDirection) {
         case TextDirection.rtl:
           _currentDragValue -= valueDelta;
           break;
         case TextDirection.ltr:
           _currentDragValue += valueDelta;
           break;
       }
       onChanged(_discretizedCurrentDragValue);
     }
   }

   void _handleDragEnd(DragEndDetails details) => _endInteraction();

   void _startInteraction(Offset globalPosition) {
     if (isInteractive) {
       if (onChangeStart != null) {
         onChangeStart(_discretizedCurrentDragValue);
       }
       _currentDragValue = _value;
       onChanged(_discretizedCurrentDragValue);
     }
   }

   void _endInteraction() {
     if (onChangeEnd != null) {
       onChangeEnd(_discretizedCurrentDragValue);
     }
     _currentDragValue = 0.0;
   }

   @override
   bool hitTestSelf(Offset position) {
     return (position.dx - _thumbCenter).abs() < CupertinoThumbPainter.radius + _kPadding;
   }

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

   @override
   void paint(PaintingContext context, Offset offset) {
     double visualPosition;
     Color leftColor;
     Color rightColor;
     switch (textDirection) {
       case TextDirection.rtl:
         visualPosition = 1.0 - _position.value;
         leftColor = _activeColor;
         rightColor = trackColor;
         break;
       case TextDirection.ltr:
         visualPosition = _position.value;
         leftColor = trackColor;
         rightColor = _activeColor;
         break;
     }

     final double trackCenter = offset.dy + size.height / 2.0;
     final double trackLeft = offset.dx + _trackLeft;
     final double trackTop = trackCenter - 1.0;
     final double trackBottom = trackCenter + 1.0;
     final double trackRight = offset.dx + _trackRight;
     final double trackActive = offset.dx + _thumbCenter;

     final Canvas canvas = context.canvas;

     if (visualPosition > 0.0) {
       final Paint paint = Paint()..color = rightColor;
       canvas.drawRRect(RRect.fromLTRBXY(trackLeft, trackTop, trackActive, trackBottom, 1.0, 1.0), paint);
     }

     if (visualPosition < 1.0) {
       final Paint paint = Paint()..color = leftColor;
       canvas.drawRRect(RRect.fromLTRBXY(trackActive, trackTop, trackRight, trackBottom, 1.0, 1.0), paint);
     }

     final Offset thumbCenter = Offset(trackActive, trackCenter);
     CupertinoThumbPainter(color: thumbColor).paint(canvas, Rect.fromCircle(center: thumbCenter, radius: CupertinoThumbPainter.radius));
   }

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

     config.isSemanticBoundary = isInteractive;
     if (isInteractive) {
       config.textDirection = textDirection;
       config.onIncrease = _increaseAction;
       config.onDecrease = _decreaseAction;
       config.value = '${(value * 100).round()}%';
       config.increasedValue = '${((value + _semanticActionUnit).clamp(0.0, 1.0) * 100).round()}%';
       config.decreasedValue = '${((value - _semanticActionUnit).clamp(0.0, 1.0) * 100).round()}%';
     }
   }

   double get _semanticActionUnit => divisions != null ? 1.0 / divisions : _kAdjustmentUnit;

   void _increaseAction() {
     if (isInteractive)
       onChanged((value + _semanticActionUnit).clamp(0.0, 1.0) as double);
   }

   void _decreaseAction() {
     if (isInteractive)
       onChanged((value - _semanticActionUnit).clamp(0.0, 1.0) as double);
   }
 }
	// 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:math' as math;
	import 'dart:ui' show lerpDouble;

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

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

	// Examples can assume:
	// int _cupertinoSliderValue = 1;
	// void setState(VoidCallback fn) { }

	/// An iOS-style slider.
	///
	/// Used to select from a range of values.
	///
	/// A slider can be used to select from either a continuous or a discrete set of
	/// values. The default is use a continuous range of values from [min] to [max].
	/// To use discrete values, use a non-null value for [divisions], which
	/// indicates the number of discrete intervals. For example, if [min] is 0.0 and
	/// [max] is 50.0 and [divisions] is 5, then the slider can take on the values
	/// discrete values 0.0, 10.0, 20.0, 30.0, 40.0, and 50.0.
	///
	/// The slider itself does not maintain any state. Instead, when the state of
	/// the slider changes, the widget calls the [onChanged] callback. Most widgets
	/// that use a slider will listen for the [onChanged] callback and rebuild the
	/// slider with a new [value] to update the visual appearance of the slider.
	///
	/// See also:
	///
	/// * <https://developer.apple.com/ios/human-interface-guidelines/controls/sliders/>
	class CupertinoSlider extends StatefulWidget {
	/// Creates an iOS-style slider.
	///
	/// The slider itself does not maintain any state. Instead, when the state of
	/// the slider changes, the widget calls the [onChanged] callback. Most widgets
	/// that use a slider will listen for the [onChanged] callback and rebuild the
	/// slider with a new [value] to update the visual appearance of the slider.
	///
	/// * [value] determines currently selected value for this slider.
	/// * [onChanged] is called when the user selects a new value for the slider.
	/// * [onChangeStart] is called when the user starts to select a new value for
	/// the slider.
	/// * [onChangeEnd] is called when the user is done selecting a new value for
	/// the slider.
	const CupertinoSlider({
	Key key,
	@required this.value,
	@required this.onChanged,
	this.onChangeStart,
	this.onChangeEnd,
	this.min = 0.0,
	this.max = 1.0,
	this.divisions,
	this.activeColor,
	this.thumbColor = CupertinoColors.white,
	}) : assert(value != null),
	assert(min != null),
	assert(max != null),
	assert(value >= min && value <= max),
	assert(divisions == null \|\| divisions > 0),
	assert(thumbColor != null),
	super(key: key);

	/// The currently selected value for this slider.
	///
	/// The slider's thumb is drawn at a position that corresponds to this value.
	final double value;

	/// Called when the user selects a new value for the slider.
	///
	/// The slider passes the new value to the callback but does not actually
	/// change state until the parent widget rebuilds the slider with the new
	/// value.
	///
	/// If null, the slider 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
	/// CupertinoSlider(
	/// value: _cupertinoSliderValue.toDouble(),
	/// min: 1.0,
	/// max: 10.0,
	/// divisions: 10,
	/// onChanged: (double newValue) {
	/// setState(() {
	/// _cupertinoSliderValue = newValue.round();
	/// });
	/// },
	/// )
	/// ```
	///
	/// See also:
	///
	/// * [onChangeStart] for a callback that is called when the user starts
	/// changing the value.
	/// * [onChangeEnd] for a callback that is called when the user stops
	/// changing the value.
	final ValueChanged<double> onChanged;

	/// Called when the user starts selecting a new value for the slider.
	///
	/// This callback shouldn't be used to update the slider [value] (use
	/// [onChanged] for that), but rather to be notified when the user has started
	/// selecting a new value by starting a drag.
	///
	/// The value passed will be the last [value] that the slider had before the
	/// change began.
	///
	/// {@tool snippet}
	///
	/// ```dart
	/// CupertinoSlider(
	/// value: _cupertinoSliderValue.toDouble(),
	/// min: 1.0,
	/// max: 10.0,
	/// divisions: 10,
	/// onChanged: (double newValue) {
	/// setState(() {
	/// _cupertinoSliderValue = newValue.round();
	/// });
	/// },
	/// onChangeStart: (double startValue) {
	/// print('Started change at $startValue');
	/// },
	/// )
	/// ```
	/// {@end-tool}
	///
	/// See also:
	///
	/// * [onChangeEnd] for a callback that is called when the value change is
	/// complete.
	final ValueChanged<double> onChangeStart;

	/// Called when the user is done selecting a new value for the slider.
	///
	/// This callback shouldn't be used to update the slider [value] (use
	/// [onChanged] for that), but rather to know when the user has completed
	/// selecting a new [value] by ending a drag.
	///
	/// {@tool snippet}
	///
	/// ```dart
	/// CupertinoSlider(
	/// value: _cupertinoSliderValue.toDouble(),
	/// min: 1.0,
	/// max: 10.0,
	/// divisions: 10,
	/// onChanged: (double newValue) {
	/// setState(() {
	/// _cupertinoSliderValue = newValue.round();
	/// });
	/// },
	/// onChangeEnd: (double newValue) {
	/// print('Ended change on $newValue');
	/// },
	/// )
	/// ```
	/// {@end-tool}
	///
	/// See also:
	///
	/// * [onChangeStart] for a callback that is called when a value change
	/// begins.
	final ValueChanged<double> onChangeEnd;

	/// The minimum value the user can select.
	///
	/// Defaults to 0.0.
	final double min;

	/// The maximum value the user can select.
	///
	/// Defaults to 1.0.
	final double max;

	/// The number of discrete divisions.
	///
	/// If null, the slider is continuous.
	final int divisions;

	/// The color to use for the portion of the slider that has been selected.
	///
	/// Defaults to the [CupertinoTheme]'s primary color if null.
	final Color activeColor;

	/// The color to use for the thumb of the slider.
	///
	/// Thumb color must not be null.
	///
	/// Defaults to [CupertinoColors.white].
	final Color thumbColor;

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

	@override
	void debugFillProperties(DiagnosticPropertiesBuilder properties) {
	super.debugFillProperties(properties);
	properties.add(DoubleProperty('value', value));
	properties.add(DoubleProperty('min', min));
	properties.add(DoubleProperty('max', max));
	}
	}

	class _CupertinoSliderState extends State<CupertinoSlider> with TickerProviderStateMixin {
	void _handleChanged(double value) {
	assert(widget.onChanged != null);
	final double lerpValue = lerpDouble(widget.min, widget.max, value);
	if (lerpValue != widget.value) {
	widget.onChanged(lerpValue);
	}
	}

	void _handleDragStart(double value) {
	assert(widget.onChangeStart != null);
	widget.onChangeStart(lerpDouble(widget.min, widget.max, value));
	}

	void _handleDragEnd(double value) {
	assert(widget.onChangeEnd != null);
	widget.onChangeEnd(lerpDouble(widget.min, widget.max, value));
	}

	@override
	Widget build(BuildContext context) {
	return _CupertinoSliderRenderObjectWidget(
	value: (widget.value - widget.min) / (widget.max - widget.min),
	divisions: widget.divisions,
	activeColor: CupertinoDynamicColor.resolve(
	widget.activeColor ?? CupertinoTheme.of(context).primaryColor,
	context,
	),
	thumbColor: widget.thumbColor,
	onChanged: widget.onChanged != null ? _handleChanged : null,
	onChangeStart: widget.onChangeStart != null ? _handleDragStart : null,
	onChangeEnd: widget.onChangeEnd != null ? _handleDragEnd : null,
	vsync: this,
	);
	}
	}

	class _CupertinoSliderRenderObjectWidget extends LeafRenderObjectWidget {
	const _CupertinoSliderRenderObjectWidget({
	Key key,
	this.value,
	this.divisions,
	this.activeColor,
	this.thumbColor,
	this.onChanged,
	this.onChangeStart,
	this.onChangeEnd,
	this.vsync,
	}) : super(key: key);

	final double value;
	final int divisions;
	final Color activeColor;
	final Color thumbColor;
	final ValueChanged<double> onChanged;
	final ValueChanged<double> onChangeStart;
	final ValueChanged<double> onChangeEnd;
	final TickerProvider vsync;

	@override
	_RenderCupertinoSlider createRenderObject(BuildContext context) {
	return _RenderCupertinoSlider(
	value: value,
	divisions: divisions,
	activeColor: activeColor,
	thumbColor: CupertinoDynamicColor.resolve(thumbColor, context),
	trackColor: CupertinoDynamicColor.resolve(CupertinoColors.systemFill, context),
	onChanged: onChanged,
	onChangeStart: onChangeStart,
	onChangeEnd: onChangeEnd,
	vsync: vsync,
	textDirection: Directionality.of(context),
	);
	}

	@override
	void updateRenderObject(BuildContext context, _RenderCupertinoSlider renderObject) {
	renderObject
	..value = value
	..divisions = divisions
	..activeColor = activeColor
	..thumbColor = CupertinoDynamicColor.resolve(thumbColor, context)
	..trackColor = CupertinoDynamicColor.resolve(CupertinoColors.systemFill, context)
	..onChanged = onChanged
	..onChangeStart = onChangeStart
	..onChangeEnd = onChangeEnd
	..textDirection = Directionality.of(context);
	// Ticker provider cannot change since there's a 1:1 relationship between
	// the _SliderRenderObjectWidget object and the _SliderState object.
	}
	}

	const double _kPadding = 8.0;
	const double _kSliderHeight = 2.0 * (CupertinoThumbPainter.radius + _kPadding);
	const double _kSliderWidth = 176.0; // Matches Material Design slider.
	const Duration _kDiscreteTransitionDuration = Duration(milliseconds: 500);

	const double _kAdjustmentUnit = 0.1; // Matches iOS implementation of material slider.

	class _RenderCupertinoSlider extends RenderConstrainedBox {
	_RenderCupertinoSlider({
	@required double value,
	int divisions,
	Color activeColor,
	Color thumbColor,
	Color trackColor,
	ValueChanged<double> onChanged,
	this.onChangeStart,
	this.onChangeEnd,
	TickerProvider vsync,
	@required TextDirection textDirection,
	}) : assert(value != null && value >= 0.0 && value <= 1.0),
	assert(textDirection != null),
	_value = value,
	_divisions = divisions,
	_activeColor = activeColor,
	_thumbColor = thumbColor,
	_trackColor = trackColor,
	_onChanged = onChanged,
	_textDirection = textDirection,
	super(additionalConstraints: const BoxConstraints.tightFor(width: _kSliderWidth, height: _kSliderHeight)) {
	_drag = HorizontalDragGestureRecognizer()
	..onStart = _handleDragStart
	..onUpdate = _handleDragUpdate
	..onEnd = _handleDragEnd;
	_position = AnimationController(
	value: value,
	duration: _kDiscreteTransitionDuration,
	vsync: vsync,
	)..addListener(markNeedsPaint);
	}

	double get value => _value;
	double _value;
	set value(double newValue) {
	assert(newValue != null && newValue >= 0.0 && newValue <= 1.0);
	if (newValue == _value)
	return;
	_value = newValue;
	if (divisions != null)
	_position.animateTo(newValue, curve: Curves.fastOutSlowIn);
	else
	_position.value = newValue;
	markNeedsSemanticsUpdate();
	}

	int get divisions => _divisions;
	int _divisions;
	set divisions(int value) {
	if (value == _divisions)
	return;
	_divisions = value;
	markNeedsPaint();
	}

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

	Color get thumbColor => _thumbColor;
	Color _thumbColor;
	set thumbColor(Color value) {
	if (value == _thumbColor)
	return;
	_thumbColor = value;
	markNeedsPaint();
	}

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

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

	ValueChanged<double> onChangeStart;
	ValueChanged<double> onChangeEnd;

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

	AnimationController _position;

	HorizontalDragGestureRecognizer _drag;
	double _currentDragValue = 0.0;

	double get _discretizedCurrentDragValue {
	double dragValue = _currentDragValue.clamp(0.0, 1.0) as double;
	if (divisions != null)
	dragValue = (dragValue * divisions).round() / divisions;
	return dragValue;
	}

	double get _trackLeft => _kPadding;
	double get _trackRight => size.width - _kPadding;
	double get _thumbCenter {
	double visualPosition;
	switch (textDirection) {
	case TextDirection.rtl:
	visualPosition = 1.0 - _value;
	break;
	case TextDirection.ltr:
	visualPosition = _value;
	break;
	}
	return lerpDouble(_trackLeft + CupertinoThumbPainter.radius, _trackRight - CupertinoThumbPainter.radius, visualPosition);
	}

	bool get isInteractive => onChanged != null;

	void _handleDragStart(DragStartDetails details) => _startInteraction(details.globalPosition);

	void _handleDragUpdate(DragUpdateDetails details) {
	if (isInteractive) {
	final double extent = math.max(_kPadding, size.width - 2.0 * (_kPadding + CupertinoThumbPainter.radius));
	final double valueDelta = details.primaryDelta / extent;
	switch (textDirection) {
	case TextDirection.rtl:
	_currentDragValue -= valueDelta;
	break;
	case TextDirection.ltr:
	_currentDragValue += valueDelta;
	break;
	}
	onChanged(_discretizedCurrentDragValue);
	}
	}

	void _handleDragEnd(DragEndDetails details) => _endInteraction();

	void _startInteraction(Offset globalPosition) {
	if (isInteractive) {
	if (onChangeStart != null) {
	onChangeStart(_discretizedCurrentDragValue);
	}
	_currentDragValue = _value;
	onChanged(_discretizedCurrentDragValue);
	}
	}

	void _endInteraction() {
	if (onChangeEnd != null) {
	onChangeEnd(_discretizedCurrentDragValue);
	}
	_currentDragValue = 0.0;
	}

	@override
	bool hitTestSelf(Offset position) {
	return (position.dx - _thumbCenter).abs() < CupertinoThumbPainter.radius + _kPadding;
	}

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

	@override
	void paint(PaintingContext context, Offset offset) {
	double visualPosition;
	Color leftColor;
	Color rightColor;
	switch (textDirection) {
	case TextDirection.rtl:
	visualPosition = 1.0 - _position.value;
	leftColor = _activeColor;
	rightColor = trackColor;
	break;
	case TextDirection.ltr:
	visualPosition = _position.value;
	leftColor = trackColor;
	rightColor = _activeColor;
	break;
	}

	final double trackCenter = offset.dy + size.height / 2.0;
	final double trackLeft = offset.dx + _trackLeft;
	final double trackTop = trackCenter - 1.0;
	final double trackBottom = trackCenter + 1.0;
	final double trackRight = offset.dx + _trackRight;
	final double trackActive = offset.dx + _thumbCenter;

	final Canvas canvas = context.canvas;

	if (visualPosition > 0.0) {
	final Paint paint = Paint()..color = rightColor;
	canvas.drawRRect(RRect.fromLTRBXY(trackLeft, trackTop, trackActive, trackBottom, 1.0, 1.0), paint);
	}

	if (visualPosition < 1.0) {
	final Paint paint = Paint()..color = leftColor;
	canvas.drawRRect(RRect.fromLTRBXY(trackActive, trackTop, trackRight, trackBottom, 1.0, 1.0), paint);
	}

	final Offset thumbCenter = Offset(trackActive, trackCenter);
	CupertinoThumbPainter(color: thumbColor).paint(canvas, Rect.fromCircle(center: thumbCenter, radius: CupertinoThumbPainter.radius));
	}

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

	config.isSemanticBoundary = isInteractive;
	if (isInteractive) {
	config.textDirection = textDirection;
	config.onIncrease = _increaseAction;
	config.onDecrease = _decreaseAction;
	config.value = '${(value * 100).round()}%';
	config.increasedValue = '${((value + _semanticActionUnit).clamp(0.0, 1.0) * 100).round()}%';
	config.decreasedValue = '${((value - _semanticActionUnit).clamp(0.0, 1.0) * 100).round()}%';
	}
	}

	double get _semanticActionUnit => divisions != null ? 1.0 / divisions : _kAdjustmentUnit;

	void _increaseAction() {
	if (isInteractive)
	onChanged((value + _semanticActionUnit).clamp(0.0, 1.0) as double);
	}

	void _decreaseAction() {
	if (isInteractive)
	onChanged((value - _semanticActionUnit).clamp(0.0, 1.0) as double);
	}
	}