packages/flutter/lib/src/material/checkbox.dart - external/github.com/flutter/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 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';

 import 'constants.dart';
 import 'debug.dart';
 import 'material_state.dart';
 import 'theme.dart';
 import 'theme_data.dart';
 import 'toggleable.dart';

 /// A material design checkbox.
 ///
 /// The checkbox itself does not maintain any state. Instead, when the state of
 /// the checkbox changes, the widget calls the [onChanged] callback. Most
 /// widgets that use a checkbox will listen for the [onChanged] callback and
 /// rebuild the checkbox with a new [value] to update the visual appearance of
 /// the checkbox.
 ///
 /// The checkbox can optionally display three values - true, false, and null -
 /// if [tristate] is true. When [value] is null a dash is displayed. By default
 /// [tristate] is false and the checkbox's [value] must be true or false.
 ///
 /// Requires one of its ancestors to be a [Material] widget.
 ///
 /// See also:
 ///
 ///  * [CheckboxListTile], which combines this widget with a [ListTile] so that
 ///    you can give the checkbox a label.
 ///  * [Switch], a widget with semantics similar to [Checkbox].
 ///  * [Radio], for selecting among a set of explicit values.
 ///  * [Slider], for selecting a value in a range.
 ///  * <https://material.io/design/components/selection-controls.html#checkboxes>
 ///  * <https://material.io/design/components/lists.html#types>
 class Checkbox extends StatefulWidget {
   /// Creates a material design checkbox.
   ///
   /// The checkbox itself does not maintain any state. Instead, when the state of
   /// the checkbox changes, the widget calls the [onChanged] callback. Most
   /// widgets that use a checkbox will listen for the [onChanged] callback and
   /// rebuild the checkbox with a new [value] to update the visual appearance of
   /// the checkbox.
   ///
   /// The following arguments are required:
   ///
   /// * [value], which determines whether the checkbox is checked. The [value]
   ///   can only be null if [tristate] is true.
   /// * [onChanged], which is called when the value of the checkbox should
   ///   change. It can be set to null to disable the checkbox.
   ///
   /// The values of [tristate] and [autofocus] must not be null.
   const Checkbox({
     Key key,
     @required this.value,
     this.tristate = false,
     @required this.onChanged,
     this.mouseCursor,
     this.activeColor,
     this.checkColor,
     this.focusColor,
     this.hoverColor,
     this.materialTapTargetSize,
     this.visualDensity,
     this.focusNode,
     this.autofocus = false,
   }) : assert(tristate != null),
        assert(tristate || value != null),
        assert(autofocus != null),
        super(key: key);

   /// Whether this checkbox is checked.
   ///
   /// This property must not be null.
   final bool value;

   /// Called when the value of the checkbox should change.
   ///
   /// The checkbox passes the new value to the callback but does not actually
   /// change state until the parent widget rebuilds the checkbox with the new
   /// value.
   ///
   /// If this callback is null, the checkbox will be displayed as disabled
   /// and will not respond to input gestures.
   ///
   /// When the checkbox is tapped, if [tristate] is false (the default) then
   /// the [onChanged] callback will be applied to `!value`. If [tristate] is
   /// true this callback cycle from false to true to null.
   ///
   /// 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
   /// Checkbox(
   ///   value: _throwShotAway,
   ///   onChanged: (bool newValue) {
   ///     setState(() {
   ///       _throwShotAway = newValue;
   ///     });
   ///   },
   /// )
   /// ```
   final ValueChanged<bool> onChanged;

   /// The cursor for a mouse pointer when it enters or is hovering over the
   /// widget.
   ///
   /// If [mouseCursor] is a [MaterialStateProperty<MouseCursor>],
   /// [MaterialStateProperty.resolve] is used for the following [MaterialState]s:
   ///
   ///  * [MaterialState.selected].
   ///  * [MaterialState.hovered].
   ///  * [MaterialState.focused].
   ///  * [MaterialState.disabled].
   ///
   /// When [value] is null and [tristate] is true, [MaterialState.selected] is
   /// included as a state.
   ///
   /// If this property is null, [MaterialStateMouseCursor.clickable] will be used.
   final MouseCursor mouseCursor;

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

   /// The color to use for the check icon when this checkbox is checked.
   ///
   /// Defaults to Color(0xFFFFFFFF)
   final Color checkColor;

   /// If true the checkbox's [value] can be true, false, or null.
   ///
   /// Checkbox displays a dash when its value is null.
   ///
   /// When a tri-state checkbox ([tristate] is true) is tapped, its [onChanged]
   /// callback will be applied to true if the current value is false, to null if
   /// value is true, and to false if value is null (i.e. it cycles through false
   /// => true => null => false when tapped).
   ///
   /// If tristate is false (the default), [value] must not be null.
   final bool tristate;

   /// Configures the minimum size of the tap target.
   ///
   /// Defaults to [ThemeData.materialTapTargetSize].
   ///
   /// See also:
   ///
   ///  * [MaterialTapTargetSize], for a description of how this affects tap targets.
   final MaterialTapTargetSize materialTapTargetSize;

   /// Defines how compact the checkbox's layout will be.
   ///
   /// {@macro flutter.material.themedata.visualDensity}
   ///
   /// See also:
   ///
   ///  * [ThemeData.visualDensity], which specifies the [density] for all widgets
   ///    within a [Theme].
   final VisualDensity visualDensity;

   /// The color for the checkbox's [Material] when it has the input focus.
   final Color focusColor;

   /// The color for the checkbox's [Material] when a pointer is hovering over it.
   final Color hoverColor;

   /// {@macro flutter.widgets.Focus.focusNode}
   final FocusNode focusNode;

   /// {@macro flutter.widgets.Focus.autofocus}
   final bool autofocus;

   /// The width of a checkbox widget.
   static const double width = 18.0;

   @override
   _CheckboxState createState() => _CheckboxState();
 }

 class _CheckboxState extends State<Checkbox> with TickerProviderStateMixin {
   bool get enabled => widget.onChanged != null;
   Map<Type, Action<Intent>> _actionMap;

   @override
   void initState() {
     super.initState();
     _actionMap = <Type, Action<Intent>>{
       ActivateIntent: CallbackAction<ActivateIntent>(onInvoke: _actionHandler),
     };
   }

   void _actionHandler(ActivateIntent intent) {
     if (widget.onChanged != null) {
       switch (widget.value) {
         case false:
           widget.onChanged(true);
           break;
         case true:
           widget.onChanged(widget.tristate ? null : false);
           break;
         default: // case null:
           widget.onChanged(false);
           break;
       }
     }
     final RenderObject renderObject = context.findRenderObject();
     renderObject.sendSemanticsEvent(const TapSemanticEvent());
   }

   bool _focused = false;
   void _handleFocusHighlightChanged(bool focused) {
     if (focused != _focused) {
       setState(() { _focused = focused; });
     }
   }

   bool _hovering = false;
   void _handleHoverChanged(bool hovering) {
     if (hovering != _hovering) {
       setState(() { _hovering = hovering; });
     }
   }

   @override
   Widget build(BuildContext context) {
     assert(debugCheckHasMaterial(context));
     final ThemeData themeData = Theme.of(context);
     Size size;
     switch (widget.materialTapTargetSize ?? themeData.materialTapTargetSize) {
       case MaterialTapTargetSize.padded:
         size = const Size(2 * kRadialReactionRadius + 8.0, 2 * kRadialReactionRadius + 8.0);
         break;
       case MaterialTapTargetSize.shrinkWrap:
         size = const Size(2 * kRadialReactionRadius, 2 * kRadialReactionRadius);
         break;
     }
     size += (widget.visualDensity ?? themeData.visualDensity).baseSizeAdjustment;
     final BoxConstraints additionalConstraints = BoxConstraints.tight(size);
     final MouseCursor effectiveMouseCursor = MaterialStateProperty.resolveAs<MouseCursor>(
       widget.mouseCursor ?? MaterialStateMouseCursor.clickable,
       <MaterialState>{
         if (!enabled) MaterialState.disabled,
         if (_hovering) MaterialState.hovered,
         if (_focused) MaterialState.focused,
         if (widget.tristate || widget.value) MaterialState.selected,
       },
     );

     return FocusableActionDetector(
       actions: _actionMap,
       focusNode: widget.focusNode,
       autofocus: widget.autofocus,
       enabled: enabled,
       onShowFocusHighlight: _handleFocusHighlightChanged,
       onShowHoverHighlight: _handleHoverChanged,
       mouseCursor: effectiveMouseCursor,
       child: Builder(
         builder: (BuildContext context) {
           return _CheckboxRenderObjectWidget(
             value: widget.value,
             tristate: widget.tristate,
             activeColor: widget.activeColor ?? themeData.toggleableActiveColor,
             checkColor: widget.checkColor ?? const Color(0xFFFFFFFF),
             inactiveColor: enabled ? themeData.unselectedWidgetColor : themeData.disabledColor,
             focusColor: widget.focusColor ?? themeData.focusColor,
             hoverColor: widget.hoverColor ?? themeData.hoverColor,
             onChanged: widget.onChanged,
             additionalConstraints: additionalConstraints,
             vsync: this,
             hasFocus: _focused,
             hovering: _hovering,
           );
         },
       ),
     );
   }
 }

 class _CheckboxRenderObjectWidget extends LeafRenderObjectWidget {
   const _CheckboxRenderObjectWidget({
     Key key,
     @required this.value,
     @required this.tristate,
     @required this.activeColor,
     @required this.checkColor,
     @required this.inactiveColor,
     @required this.focusColor,
     @required this.hoverColor,
     @required this.onChanged,
     @required this.vsync,
     @required this.additionalConstraints,
     @required this.hasFocus,
     @required this.hovering,
   }) : assert(tristate != null),
        assert(tristate || value != null),
        assert(activeColor != null),
        assert(inactiveColor != null),
        assert(vsync != null),
        super(key: key);

   final bool value;
   final bool tristate;
   final bool hasFocus;
   final bool hovering;
   final Color activeColor;
   final Color checkColor;
   final Color inactiveColor;
   final Color focusColor;
   final Color hoverColor;
   final ValueChanged<bool> onChanged;
   final TickerProvider vsync;
   final BoxConstraints additionalConstraints;

   @override
   _RenderCheckbox createRenderObject(BuildContext context) => _RenderCheckbox(
     value: value,
     tristate: tristate,
     activeColor: activeColor,
     checkColor: checkColor,
     inactiveColor: inactiveColor,
     focusColor: focusColor,
     hoverColor: hoverColor,
     onChanged: onChanged,
     vsync: vsync,
     additionalConstraints: additionalConstraints,
     hasFocus: hasFocus,
     hovering: hovering,
   );

   @override
   void updateRenderObject(BuildContext context, _RenderCheckbox renderObject) {
     renderObject
       // The `tristate` must be changed before `value` due to the assertion at
       // the beginning of `set value`.
       ..tristate = tristate
       ..value = value
       ..activeColor = activeColor
       ..checkColor = checkColor
       ..inactiveColor = inactiveColor
       ..focusColor = focusColor
       ..hoverColor = hoverColor
       ..onChanged = onChanged
       ..additionalConstraints = additionalConstraints
       ..vsync = vsync
       ..hasFocus = hasFocus
       ..hovering = hovering;
   }
 }

 const double _kEdgeSize = Checkbox.width;
 const Radius _kEdgeRadius = Radius.circular(1.0);
 const double _kStrokeWidth = 2.0;

 class _RenderCheckbox extends RenderToggleable {
   _RenderCheckbox({
     bool value,
     bool tristate,
     Color activeColor,
     this.checkColor,
     Color inactiveColor,
     Color focusColor,
     Color hoverColor,
     BoxConstraints additionalConstraints,
     ValueChanged<bool> onChanged,
     bool hasFocus,
     bool hovering,
     @required TickerProvider vsync,
   }) : _oldValue = value,
        super(
          value: value,
          tristate: tristate,
          activeColor: activeColor,
          inactiveColor: inactiveColor,
          focusColor: focusColor,
          hoverColor: hoverColor,
          onChanged: onChanged,
          additionalConstraints: additionalConstraints,
          vsync: vsync,
          hasFocus: hasFocus,
          hovering: hovering,
        );

   bool _oldValue;
   Color checkColor;

   @override
   set value(bool newValue) {
     if (newValue == value)
       return;
     _oldValue = value;
     super.value = newValue;
   }

   @override
   void describeSemanticsConfiguration(SemanticsConfiguration config) {
     super.describeSemanticsConfiguration(config);
     config.isChecked = value == true;
   }

   // The square outer bounds of the checkbox at t, with the specified origin.
   // At t == 0.0, the outer rect's size is _kEdgeSize (Checkbox.width)
   // At t == 0.5, .. is _kEdgeSize - _kStrokeWidth
   // At t == 1.0, .. is _kEdgeSize
   RRect _outerRectAt(Offset origin, double t) {
     final double inset = 1.0 - (t - 0.5).abs() * 2.0;
     final double size = _kEdgeSize - inset * _kStrokeWidth;
     final Rect rect = Rect.fromLTWH(origin.dx + inset, origin.dy + inset, size, size);
     return RRect.fromRectAndRadius(rect, _kEdgeRadius);
   }

   // The checkbox's border color if value == false, or its fill color when
   // value == true or null.
   Color _colorAt(double t) {
     // As t goes from 0.0 to 0.25, animate from the inactiveColor to activeColor.
     return onChanged == null
       ? inactiveColor
       : (t >= 0.25 ? activeColor : Color.lerp(inactiveColor, activeColor, t * 4.0));
   }

   // White stroke used to paint the check and dash.
   Paint _createStrokePaint() {
     return Paint()
       ..color = checkColor
       ..style = PaintingStyle.stroke
       ..strokeWidth = _kStrokeWidth;
   }

   void _drawBorder(Canvas canvas, RRect outer, double t, Paint paint) {
     assert(t >= 0.0 && t <= 0.5);
     final double size = outer.width;
     // As t goes from 0.0 to 1.0, gradually fill the outer RRect.
     final RRect inner = outer.deflate(math.min(size / 2.0, _kStrokeWidth + size * t));
     canvas.drawDRRect(outer, inner, paint);
   }

   void _drawCheck(Canvas canvas, Offset origin, double t, Paint paint) {
     assert(t >= 0.0 && t <= 1.0);
     // As t goes from 0.0 to 1.0, animate the two check mark strokes from the
     // short side to the long side.
     final Path path = Path();
     const Offset start = Offset(_kEdgeSize * 0.15, _kEdgeSize * 0.45);
     const Offset mid = Offset(_kEdgeSize * 0.4, _kEdgeSize * 0.7);
     const Offset end = Offset(_kEdgeSize * 0.85, _kEdgeSize * 0.25);
     if (t < 0.5) {
       final double strokeT = t * 2.0;
       final Offset drawMid = Offset.lerp(start, mid, strokeT);
       path.moveTo(origin.dx + start.dx, origin.dy + start.dy);
       path.lineTo(origin.dx + drawMid.dx, origin.dy + drawMid.dy);
     } else {
       final double strokeT = (t - 0.5) * 2.0;
       final Offset drawEnd = Offset.lerp(mid, end, strokeT);
       path.moveTo(origin.dx + start.dx, origin.dy + start.dy);
       path.lineTo(origin.dx + mid.dx, origin.dy + mid.dy);
       path.lineTo(origin.dx + drawEnd.dx, origin.dy + drawEnd.dy);
     }
     canvas.drawPath(path, paint);
   }

   void _drawDash(Canvas canvas, Offset origin, double t, Paint paint) {
     assert(t >= 0.0 && t <= 1.0);
     // As t goes from 0.0 to 1.0, animate the horizontal line from the
     // mid point outwards.
     const Offset start = Offset(_kEdgeSize * 0.2, _kEdgeSize * 0.5);
     const Offset mid = Offset(_kEdgeSize * 0.5, _kEdgeSize * 0.5);
     const Offset end = Offset(_kEdgeSize * 0.8, _kEdgeSize * 0.5);
     final Offset drawStart = Offset.lerp(start, mid, 1.0 - t);
     final Offset drawEnd = Offset.lerp(mid, end, t);
     canvas.drawLine(origin + drawStart, origin + drawEnd, paint);
   }

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

     final Paint strokePaint = _createStrokePaint();
     final Offset origin = offset + (size / 2.0 - const Size.square(_kEdgeSize) / 2.0 as Offset);
     final AnimationStatus status = position.status;
     final double tNormalized = status == AnimationStatus.forward || status == AnimationStatus.completed
       ? position.value
       : 1.0 - position.value;

     // Four cases: false to null, false to true, null to false, true to false
     if (_oldValue == false || value == false) {
       final double t = value == false ? 1.0 - tNormalized : tNormalized;
       final RRect outer = _outerRectAt(origin, t);
       final Paint paint = Paint()..color = _colorAt(t);

       if (t <= 0.5) {
         _drawBorder(canvas, outer, t, paint);
       } else {
         canvas.drawRRect(outer, paint);

         final double tShrink = (t - 0.5) * 2.0;
         if (_oldValue == null || value == null)
           _drawDash(canvas, origin, tShrink, strokePaint);
         else
           _drawCheck(canvas, origin, tShrink, strokePaint);
       }
     } else { // Two cases: null to true, true to null
       final RRect outer = _outerRectAt(origin, 1.0);
       final Paint paint = Paint() ..color = _colorAt(1.0);
       canvas.drawRRect(outer, paint);

       if (tNormalized <= 0.5) {
         final double tShrink = 1.0 - tNormalized * 2.0;
         if (_oldValue == true)
           _drawCheck(canvas, origin, tShrink, strokePaint);
         else
           _drawDash(canvas, origin, tShrink, strokePaint);
       } else {
         final double tExpand = (tNormalized - 0.5) * 2.0;
         if (value == true)
           _drawCheck(canvas, origin, tExpand, strokePaint);
         else
           _drawDash(canvas, origin, tExpand, strokePaint);
       }
     }
   }
 }
	// 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 'package:flutter/foundation.dart';
	import 'package:flutter/gestures.dart';
	import 'package:flutter/rendering.dart';
	import 'package:flutter/widgets.dart';

	import 'constants.dart';
	import 'debug.dart';
	import 'material_state.dart';
	import 'theme.dart';
	import 'theme_data.dart';
	import 'toggleable.dart';

	/// A material design checkbox.
	///
	/// The checkbox itself does not maintain any state. Instead, when the state of
	/// the checkbox changes, the widget calls the [onChanged] callback. Most
	/// widgets that use a checkbox will listen for the [onChanged] callback and
	/// rebuild the checkbox with a new [value] to update the visual appearance of
	/// the checkbox.
	///
	/// The checkbox can optionally display three values - true, false, and null -
	/// if [tristate] is true. When [value] is null a dash is displayed. By default
	/// [tristate] is false and the checkbox's [value] must be true or false.
	///
	/// Requires one of its ancestors to be a [Material] widget.
	///
	/// See also:
	///
	/// * [CheckboxListTile], which combines this widget with a [ListTile] so that
	/// you can give the checkbox a label.
	/// * [Switch], a widget with semantics similar to [Checkbox].
	/// * [Radio], for selecting among a set of explicit values.
	/// * [Slider], for selecting a value in a range.
	/// * <https://material.io/design/components/selection-controls.html#checkboxes>
	/// * <https://material.io/design/components/lists.html#types>
	class Checkbox extends StatefulWidget {
	/// Creates a material design checkbox.
	///
	/// The checkbox itself does not maintain any state. Instead, when the state of
	/// the checkbox changes, the widget calls the [onChanged] callback. Most
	/// widgets that use a checkbox will listen for the [onChanged] callback and
	/// rebuild the checkbox with a new [value] to update the visual appearance of
	/// the checkbox.
	///
	/// The following arguments are required:
	///
	/// * [value], which determines whether the checkbox is checked. The [value]
	/// can only be null if [tristate] is true.
	/// * [onChanged], which is called when the value of the checkbox should
	/// change. It can be set to null to disable the checkbox.
	///
	/// The values of [tristate] and [autofocus] must not be null.
	const Checkbox({
	Key key,
	@required this.value,
	this.tristate = false,
	@required this.onChanged,
	this.mouseCursor,
	this.activeColor,
	this.checkColor,
	this.focusColor,
	this.hoverColor,
	this.materialTapTargetSize,
	this.visualDensity,
	this.focusNode,
	this.autofocus = false,
	}) : assert(tristate != null),
	assert(tristate \|\| value != null),
	assert(autofocus != null),
	super(key: key);

	/// Whether this checkbox is checked.
	///
	/// This property must not be null.
	final bool value;

	/// Called when the value of the checkbox should change.
	///
	/// The checkbox passes the new value to the callback but does not actually
	/// change state until the parent widget rebuilds the checkbox with the new
	/// value.
	///
	/// If this callback is null, the checkbox will be displayed as disabled
	/// and will not respond to input gestures.
	///
	/// When the checkbox is tapped, if [tristate] is false (the default) then
	/// the [onChanged] callback will be applied to `!value`. If [tristate] is
	/// true this callback cycle from false to true to null.
	///
	/// 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
	/// Checkbox(
	/// value: _throwShotAway,
	/// onChanged: (bool newValue) {
	/// setState(() {
	/// _throwShotAway = newValue;
	/// });
	/// },
	/// )
	/// ```
	final ValueChanged<bool> onChanged;

	/// The cursor for a mouse pointer when it enters or is hovering over the
	/// widget.
	///
	/// If [mouseCursor] is a [MaterialStateProperty<MouseCursor>],
	/// [MaterialStateProperty.resolve] is used for the following [MaterialState]s:
	///
	/// * [MaterialState.selected].
	/// * [MaterialState.hovered].
	/// * [MaterialState.focused].
	/// * [MaterialState.disabled].
	///
	/// When [value] is null and [tristate] is true, [MaterialState.selected] is
	/// included as a state.
	///
	/// If this property is null, [MaterialStateMouseCursor.clickable] will be used.
	final MouseCursor mouseCursor;

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

	/// The color to use for the check icon when this checkbox is checked.
	///
	/// Defaults to Color(0xFFFFFFFF)
	final Color checkColor;

	/// If true the checkbox's [value] can be true, false, or null.
	///
	/// Checkbox displays a dash when its value is null.
	///
	/// When a tri-state checkbox ([tristate] is true) is tapped, its [onChanged]
	/// callback will be applied to true if the current value is false, to null if
	/// value is true, and to false if value is null (i.e. it cycles through false
	/// => true => null => false when tapped).
	///
	/// If tristate is false (the default), [value] must not be null.
	final bool tristate;

	/// Configures the minimum size of the tap target.
	///
	/// Defaults to [ThemeData.materialTapTargetSize].
	///
	/// See also:
	///
	/// * [MaterialTapTargetSize], for a description of how this affects tap targets.
	final MaterialTapTargetSize materialTapTargetSize;

	/// Defines how compact the checkbox's layout will be.
	///
	/// {@macro flutter.material.themedata.visualDensity}
	///
	/// See also:
	///
	/// * [ThemeData.visualDensity], which specifies the [density] for all widgets
	/// within a [Theme].
	final VisualDensity visualDensity;

	/// The color for the checkbox's [Material] when it has the input focus.
	final Color focusColor;

	/// The color for the checkbox's [Material] when a pointer is hovering over it.
	final Color hoverColor;

	/// {@macro flutter.widgets.Focus.focusNode}
	final FocusNode focusNode;

	/// {@macro flutter.widgets.Focus.autofocus}
	final bool autofocus;

	/// The width of a checkbox widget.
	static const double width = 18.0;

	@override
	_CheckboxState createState() => _CheckboxState();
	}

	class _CheckboxState extends State<Checkbox> with TickerProviderStateMixin {
	bool get enabled => widget.onChanged != null;
	Map<Type, Action<Intent>> _actionMap;

	@override
	void initState() {
	super.initState();
	_actionMap = <Type, Action<Intent>>{
	ActivateIntent: CallbackAction<ActivateIntent>(onInvoke: _actionHandler),
	};
	}

	void _actionHandler(ActivateIntent intent) {
	if (widget.onChanged != null) {
	switch (widget.value) {
	case false:
	widget.onChanged(true);
	break;
	case true:
	widget.onChanged(widget.tristate ? null : false);
	break;
	default: // case null:
	widget.onChanged(false);
	break;
	}
	}
	final RenderObject renderObject = context.findRenderObject();
	renderObject.sendSemanticsEvent(const TapSemanticEvent());
	}

	bool _focused = false;
	void _handleFocusHighlightChanged(bool focused) {
	if (focused != _focused) {
	setState(() { _focused = focused; });
	}
	}

	bool _hovering = false;
	void _handleHoverChanged(bool hovering) {
	if (hovering != _hovering) {
	setState(() { _hovering = hovering; });
	}
	}

	@override
	Widget build(BuildContext context) {
	assert(debugCheckHasMaterial(context));
	final ThemeData themeData = Theme.of(context);
	Size size;
	switch (widget.materialTapTargetSize ?? themeData.materialTapTargetSize) {
	case MaterialTapTargetSize.padded:
	size = const Size(2 * kRadialReactionRadius + 8.0, 2 * kRadialReactionRadius + 8.0);
	break;
	case MaterialTapTargetSize.shrinkWrap:
	size = const Size(2 * kRadialReactionRadius, 2 * kRadialReactionRadius);
	break;
	}
	size += (widget.visualDensity ?? themeData.visualDensity).baseSizeAdjustment;
	final BoxConstraints additionalConstraints = BoxConstraints.tight(size);
	final MouseCursor effectiveMouseCursor = MaterialStateProperty.resolveAs<MouseCursor>(
	widget.mouseCursor ?? MaterialStateMouseCursor.clickable,
	<MaterialState>{
	if (!enabled) MaterialState.disabled,
	if (_hovering) MaterialState.hovered,
	if (_focused) MaterialState.focused,
	if (widget.tristate \|\| widget.value) MaterialState.selected,
	},
	);

	return FocusableActionDetector(
	actions: _actionMap,
	focusNode: widget.focusNode,
	autofocus: widget.autofocus,
	enabled: enabled,
	onShowFocusHighlight: _handleFocusHighlightChanged,
	onShowHoverHighlight: _handleHoverChanged,
	mouseCursor: effectiveMouseCursor,
	child: Builder(
	builder: (BuildContext context) {
	return _CheckboxRenderObjectWidget(
	value: widget.value,
	tristate: widget.tristate,
	activeColor: widget.activeColor ?? themeData.toggleableActiveColor,
	checkColor: widget.checkColor ?? const Color(0xFFFFFFFF),
	inactiveColor: enabled ? themeData.unselectedWidgetColor : themeData.disabledColor,
	focusColor: widget.focusColor ?? themeData.focusColor,
	hoverColor: widget.hoverColor ?? themeData.hoverColor,
	onChanged: widget.onChanged,
	additionalConstraints: additionalConstraints,
	vsync: this,
	hasFocus: _focused,
	hovering: _hovering,
	);
	},
	),
	);
	}
	}

	class _CheckboxRenderObjectWidget extends LeafRenderObjectWidget {
	const _CheckboxRenderObjectWidget({
	Key key,
	@required this.value,
	@required this.tristate,
	@required this.activeColor,
	@required this.checkColor,
	@required this.inactiveColor,
	@required this.focusColor,
	@required this.hoverColor,
	@required this.onChanged,
	@required this.vsync,
	@required this.additionalConstraints,
	@required this.hasFocus,
	@required this.hovering,
	}) : assert(tristate != null),
	assert(tristate \|\| value != null),
	assert(activeColor != null),
	assert(inactiveColor != null),
	assert(vsync != null),
	super(key: key);

	final bool value;
	final bool tristate;
	final bool hasFocus;
	final bool hovering;
	final Color activeColor;
	final Color checkColor;
	final Color inactiveColor;
	final Color focusColor;
	final Color hoverColor;
	final ValueChanged<bool> onChanged;
	final TickerProvider vsync;
	final BoxConstraints additionalConstraints;

	@override
	_RenderCheckbox createRenderObject(BuildContext context) => _RenderCheckbox(
	value: value,
	tristate: tristate,
	activeColor: activeColor,
	checkColor: checkColor,
	inactiveColor: inactiveColor,
	focusColor: focusColor,
	hoverColor: hoverColor,
	onChanged: onChanged,
	vsync: vsync,
	additionalConstraints: additionalConstraints,
	hasFocus: hasFocus,
	hovering: hovering,
	);

	@override
	void updateRenderObject(BuildContext context, _RenderCheckbox renderObject) {
	renderObject
	// The `tristate` must be changed before `value` due to the assertion at
	// the beginning of `set value`.
	..tristate = tristate
	..value = value
	..activeColor = activeColor
	..checkColor = checkColor
	..inactiveColor = inactiveColor
	..focusColor = focusColor
	..hoverColor = hoverColor
	..onChanged = onChanged
	..additionalConstraints = additionalConstraints
	..vsync = vsync
	..hasFocus = hasFocus
	..hovering = hovering;
	}
	}

	const double _kEdgeSize = Checkbox.width;
	const Radius _kEdgeRadius = Radius.circular(1.0);
	const double _kStrokeWidth = 2.0;

	class _RenderCheckbox extends RenderToggleable {
	_RenderCheckbox({
	bool value,
	bool tristate,
	Color activeColor,
	this.checkColor,
	Color inactiveColor,
	Color focusColor,
	Color hoverColor,
	BoxConstraints additionalConstraints,
	ValueChanged<bool> onChanged,
	bool hasFocus,
	bool hovering,
	@required TickerProvider vsync,
	}) : _oldValue = value,
	super(
	value: value,
	tristate: tristate,
	activeColor: activeColor,
	inactiveColor: inactiveColor,
	focusColor: focusColor,
	hoverColor: hoverColor,
	onChanged: onChanged,
	additionalConstraints: additionalConstraints,
	vsync: vsync,
	hasFocus: hasFocus,
	hovering: hovering,
	);

	bool _oldValue;
	Color checkColor;

	@override
	set value(bool newValue) {
	if (newValue == value)
	return;
	_oldValue = value;
	super.value = newValue;
	}

	@override
	void describeSemanticsConfiguration(SemanticsConfiguration config) {
	super.describeSemanticsConfiguration(config);
	config.isChecked = value == true;
	}

	// The square outer bounds of the checkbox at t, with the specified origin.
	// At t == 0.0, the outer rect's size is _kEdgeSize (Checkbox.width)
	// At t == 0.5, .. is _kEdgeSize - _kStrokeWidth
	// At t == 1.0, .. is _kEdgeSize
	RRect _outerRectAt(Offset origin, double t) {
	final double inset = 1.0 - (t - 0.5).abs() * 2.0;
	final double size = _kEdgeSize - inset * _kStrokeWidth;
	final Rect rect = Rect.fromLTWH(origin.dx + inset, origin.dy + inset, size, size);
	return RRect.fromRectAndRadius(rect, _kEdgeRadius);
	}

	// The checkbox's border color if value == false, or its fill color when
	// value == true or null.
	Color _colorAt(double t) {
	// As t goes from 0.0 to 0.25, animate from the inactiveColor to activeColor.
	return onChanged == null
	? inactiveColor
	: (t >= 0.25 ? activeColor : Color.lerp(inactiveColor, activeColor, t * 4.0));
	}

	// White stroke used to paint the check and dash.
	Paint _createStrokePaint() {
	return Paint()
	..color = checkColor
	..style = PaintingStyle.stroke
	..strokeWidth = _kStrokeWidth;
	}

	void _drawBorder(Canvas canvas, RRect outer, double t, Paint paint) {
	assert(t >= 0.0 && t <= 0.5);
	final double size = outer.width;
	// As t goes from 0.0 to 1.0, gradually fill the outer RRect.
	final RRect inner = outer.deflate(math.min(size / 2.0, _kStrokeWidth + size * t));
	canvas.drawDRRect(outer, inner, paint);
	}

	void _drawCheck(Canvas canvas, Offset origin, double t, Paint paint) {
	assert(t >= 0.0 && t <= 1.0);
	// As t goes from 0.0 to 1.0, animate the two check mark strokes from the
	// short side to the long side.
	final Path path = Path();
	const Offset start = Offset(_kEdgeSize * 0.15, _kEdgeSize * 0.45);
	const Offset mid = Offset(_kEdgeSize * 0.4, _kEdgeSize * 0.7);
	const Offset end = Offset(_kEdgeSize * 0.85, _kEdgeSize * 0.25);
	if (t < 0.5) {
	final double strokeT = t * 2.0;
	final Offset drawMid = Offset.lerp(start, mid, strokeT);
	path.moveTo(origin.dx + start.dx, origin.dy + start.dy);
	path.lineTo(origin.dx + drawMid.dx, origin.dy + drawMid.dy);
	} else {
	final double strokeT = (t - 0.5) * 2.0;
	final Offset drawEnd = Offset.lerp(mid, end, strokeT);
	path.moveTo(origin.dx + start.dx, origin.dy + start.dy);
	path.lineTo(origin.dx + mid.dx, origin.dy + mid.dy);
	path.lineTo(origin.dx + drawEnd.dx, origin.dy + drawEnd.dy);
	}
	canvas.drawPath(path, paint);
	}

	void _drawDash(Canvas canvas, Offset origin, double t, Paint paint) {
	assert(t >= 0.0 && t <= 1.0);
	// As t goes from 0.0 to 1.0, animate the horizontal line from the
	// mid point outwards.
	const Offset start = Offset(_kEdgeSize * 0.2, _kEdgeSize * 0.5);
	const Offset mid = Offset(_kEdgeSize * 0.5, _kEdgeSize * 0.5);
	const Offset end = Offset(_kEdgeSize * 0.8, _kEdgeSize * 0.5);
	final Offset drawStart = Offset.lerp(start, mid, 1.0 - t);
	final Offset drawEnd = Offset.lerp(mid, end, t);
	canvas.drawLine(origin + drawStart, origin + drawEnd, paint);
	}

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

	final Paint strokePaint = _createStrokePaint();
	final Offset origin = offset + (size / 2.0 - const Size.square(_kEdgeSize) / 2.0 as Offset);
	final AnimationStatus status = position.status;
	final double tNormalized = status == AnimationStatus.forward \|\| status == AnimationStatus.completed
	? position.value
	: 1.0 - position.value;

	// Four cases: false to null, false to true, null to false, true to false
	if (_oldValue == false \|\| value == false) {
	final double t = value == false ? 1.0 - tNormalized : tNormalized;
	final RRect outer = _outerRectAt(origin, t);
	final Paint paint = Paint()..color = _colorAt(t);

	if (t <= 0.5) {
	_drawBorder(canvas, outer, t, paint);
	} else {
	canvas.drawRRect(outer, paint);

	final double tShrink = (t - 0.5) * 2.0;
	if (_oldValue == null \|\| value == null)
	_drawDash(canvas, origin, tShrink, strokePaint);
	else
	_drawCheck(canvas, origin, tShrink, strokePaint);
	}
	} else { // Two cases: null to true, true to null
	final RRect outer = _outerRectAt(origin, 1.0);
	final Paint paint = Paint() ..color = _colorAt(1.0);
	canvas.drawRRect(outer, paint);

	if (tNormalized <= 0.5) {
	final double tShrink = 1.0 - tNormalized * 2.0;
	if (_oldValue == true)
	_drawCheck(canvas, origin, tShrink, strokePaint);
	else
	_drawDash(canvas, origin, tShrink, strokePaint);
	} else {
	final double tExpand = (tNormalized - 0.5) * 2.0;
	if (value == true)
	_drawCheck(canvas, origin, tExpand, strokePaint);
	else
	_drawDash(canvas, origin, tExpand, strokePaint);
	}
	}
	}
	}