com.unity.uiwidgets/com.unity.uiwidgets/Runtime/cupertino/segmented_control.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Unity.UIWidgets.animation;
using Unity.UIWidgets.ui;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.gestures;
using Unity.UIWidgets.widgets;
using Unity.UIWidgets.painting;
using Unity.UIWidgets.rendering;
using UnityEngine;
using Color = Unity.UIWidgets.ui.Color;
using Rect = Unity.UIWidgets.ui.Rect;
using TextStyle = Unity.UIWidgets.painting.TextStyle;

namespace Unity.UIWidgets.cupertino {
    class CupertinoSegmentedControlsUtils {
        public static readonly EdgeInsetsGeometry _kHorizontalItemPadding = EdgeInsets.symmetric(horizontal: 16.0f);
        public const float _kMinSegmentedControlHeight = 28.0f;
        public static readonly TimeSpan _kFadeDuration = TimeSpan.FromMilliseconds(165);
    }

    public class CupertinoSegmentedControl<T> : StatefulWidget {
        public CupertinoSegmentedControl(
        Key key = null,
        Dictionary<T, Widget> children = null,
        ValueChanged<T> onValueChanged = null,
        T groupValue = default,
        Color unselectedColor = null,
        Color selectedColor = null,
        Color borderColor = null,
        Color pressedColor = null,
        EdgeInsetsGeometry padding = null
        ) :base(key: key) 
        { D.assert(children != null);
          D.assert(children.Count >= 2);
          D.assert(onValueChanged != null);
          D.assert(
              groupValue == null || children.Keys.Any((T child) => child.Equals(groupValue)), () =>
                  "The groupValue must be either null or one of the keys in the children map."
          );
          this.children = children;
          this.onValueChanged = onValueChanged;
          this.groupValue = groupValue;
          this.unselectedColor = unselectedColor;
          this.selectedColor = selectedColor;
          this.borderColor = borderColor;
          this.pressedColor = pressedColor;
          this.padding = padding;

        }
      public readonly Dictionary<T, Widget> children;
      public readonly T groupValue;
      public readonly ValueChanged<T> onValueChanged;
      public readonly Color unselectedColor; 
      public readonly Color selectedColor;
      public readonly Color borderColor;
      public readonly Color pressedColor;
      public readonly EdgeInsetsGeometry padding;

      public override State createState() {
          return  new _SegmentedControlState<T>();
      }
    }
    class _SegmentedControlState<T> : TickerProviderStateMixin<CupertinoSegmentedControl<T>> {
      T _pressedKey;

      public readonly List<AnimationController> _selectionControllers = new List<AnimationController>();
      public readonly List<ColorTween> _childTweens = new List<ColorTween>();

      ColorTween _forwardBackgroundColorTween;
      ColorTween _reverseBackgroundColorTween;
      ColorTween _textColorTween;

      Color _selectedColor;
      Color _unselectedColor;
      Color _borderColor;
      Color _pressedColor;

      AnimationController createAnimationController() {
          var controller = new AnimationController(
              duration: CupertinoSegmentedControlsUtils._kFadeDuration,
              vsync: this
            );
          controller.addListener(()=> {
              setState(() =>{
                        // State of background/text colors has changed
                      });
          });
          return controller;
      }

      bool _updateColors() {
        D.assert(mounted, ()=>"This should only be called after didUpdateDependencies");
        bool changed = false;
         Color selectedColor = widget.selectedColor ?? CupertinoTheme.of(context).primaryColor;
        if (_selectedColor != selectedColor) {
          changed = true;
          _selectedColor = selectedColor;
        }
         Color unselectedColor = widget.unselectedColor ?? CupertinoTheme.of(context).primaryContrastingColor;
        if (_unselectedColor != unselectedColor) {
          changed = true;
          _unselectedColor = unselectedColor;
        }
         Color borderColor = widget.borderColor ?? CupertinoTheme.of(context).primaryColor;
        if (_borderColor != borderColor) {
          changed = true;
          _borderColor = borderColor;
        }
         Color pressedColor = widget.pressedColor ?? CupertinoTheme.of(context).primaryColor.withOpacity(0.2f);
        if (_pressedColor != pressedColor) {
          changed = true;
          _pressedColor = pressedColor;
        }

        _forwardBackgroundColorTween = new ColorTween(
          begin: _pressedColor,
          end: _selectedColor
        );
        _reverseBackgroundColorTween = new ColorTween(
          begin: _unselectedColor,
          end: _selectedColor
        );
        _textColorTween = new ColorTween(
          begin: _selectedColor,
          end: _unselectedColor
        );
        return changed;
      }

      void _updateAnimationControllers() {
        D.assert(mounted, ()=>"This should only be called after didUpdateDependencies");
        foreach ( AnimationController controller in _selectionControllers) {
          controller.dispose();
        }
        _selectionControllers.Clear();
        _childTweens.Clear();
        foreach ( T key in widget.children.Keys) {
           AnimationController animationController = createAnimationController();
          if (widget.groupValue.Equals(key)) {
            _childTweens.Add(_reverseBackgroundColorTween);
            animationController.setValue(1.0f);
          } else {
            _childTweens.Add(_forwardBackgroundColorTween);
          }
          _selectionControllers.Add(animationController);
        }
      }

      public override void didChangeDependencies() {
        base.didChangeDependencies();

        if (_updateColors()) {
          _updateAnimationControllers();
        }
      }

      public override void didUpdateWidget(StatefulWidget oldWidget) { 
          oldWidget = (CupertinoSegmentedControl<T>) oldWidget;
        base.didUpdateWidget(oldWidget);

        if (_updateColors() || ((CupertinoSegmentedControl<T>) oldWidget).children.Count != widget.children.Count) {
          _updateAnimationControllers();
        }

        if (!((CupertinoSegmentedControl<T>)oldWidget).groupValue.Equals(widget.groupValue)) {
          int index = 0;
          foreach ( T key in widget.children.Keys) {
            if (widget.groupValue.Equals(key)) {
              _childTweens[index] = _forwardBackgroundColorTween;
              _selectionControllers[index].forward();
            } else {
              _childTweens[index] = _reverseBackgroundColorTween;
              _selectionControllers[index].reverse();
            }
            index += 1;
          }
        }
      }

      public override void dispose() {
          foreach( AnimationController animationController in _selectionControllers) {
          animationController.dispose();
        }
        base.dispose();
      }


      void _onTapDown(T currentKey) {
        if (_pressedKey == null && !currentKey.Equals(widget.groupValue)) {
          setState(()=> {
            _pressedKey = currentKey;
          });
        }
      }

      void _onTapCancel() {
        setState(()=> {
          _pressedKey = default(T);
        });
      }

      void _onTap(T currentKey) {
        if (!currentKey.Equals( _pressedKey))
          return;
        if (!currentKey.Equals(widget.groupValue)) {
          widget.onValueChanged(currentKey);
        }
        _pressedKey = default;
      }

      Color getTextColor(int index, T currentKey) {
        if (_selectionControllers[index].isAnimating)
          return _textColorTween.evaluate(_selectionControllers[index]);
        if (widget.groupValue.Equals(currentKey))
          return _unselectedColor;
        return _selectedColor;
      }

      Color getBackgroundColor(int index, T currentKey) {
        if (_selectionControllers[index].isAnimating)
          return _childTweens[index].evaluate(_selectionControllers[index]);
        if (widget.groupValue.Equals(currentKey))
          return _selectedColor;
        if (_pressedKey.Equals(currentKey))
          return _pressedColor;
        return _unselectedColor;
      }

      public override Widget build(BuildContext context) {
         List<Widget> _gestureChildren = new List<Widget>();
         List<Color> _backgroundColors = new List<Color>();
        int index = 0;
        int selectedIndex = 0;
        int pressedIndex = 0;
        foreach ( T currentKey in widget.children.Keys) {
          selectedIndex = (widget.groupValue.Equals(currentKey)) ? index : selectedIndex;
          pressedIndex = (_pressedKey.Equals(currentKey)) ? index : pressedIndex;
          TextStyle textStyle = DefaultTextStyle.of(context).style.copyWith(
            color: getTextColor(index, currentKey)
          );
           IconThemeData iconTheme = new IconThemeData(
            color: getTextColor(index, currentKey)
          );

          Widget child = new Center(
            child: widget.children[currentKey]
          );

          child = new GestureDetector(
            onTapDown: (TapDownDetails _event)=> {
              _onTapDown(currentKey);
            },
            onTapCancel: _onTapCancel,
            onTap: ()=> {
              _onTap(currentKey);
            },
            child: new IconTheme(
              data: iconTheme,
              child: new DefaultTextStyle(
                style: textStyle,
                child: child 
              )
            )
          );

          _backgroundColors.Add(getBackgroundColor(index, currentKey));
          _gestureChildren.Add(child);
          index += 1;
        }

         Widget box = new _SegmentedControlRenderWidget<T>(
          children: _gestureChildren,
          selectedIndex: selectedIndex,
          pressedIndex: pressedIndex,
          backgroundColors: _backgroundColors,
          borderColor: _borderColor
        );

        return new Padding(
          padding: widget.padding ?? CupertinoSegmentedControlsUtils._kHorizontalItemPadding,
          child: new UnconstrainedBox(
            constrainedAxis: Axis.horizontal,
            child: box
          )
        );
      }
    }
    public class _SegmentedControlRenderWidget<T> : MultiChildRenderObjectWidget {
        public _SegmentedControlRenderWidget(
        Key key = null,
        List<Widget> children = null,
        int? selectedIndex = null,
        int? pressedIndex = null, 
        List<Color> backgroundColors = null,
        Color borderColor = null
      ) : base(
              key: key,
              children: children ?? new List<Widget>()
            ) {
               this.selectedIndex = selectedIndex;
               this.pressedIndex = pressedIndex;
               this.backgroundColors = backgroundColors;
               this.borderColor = borderColor;
      }

      public readonly int? selectedIndex;
      public readonly int? pressedIndex;
      public readonly List<Color> backgroundColors;
      public readonly Color borderColor;
      public override RenderObject createRenderObject(BuildContext context) {
        return new _RenderSegmentedControl<T>(
          textDirection: Directionality.of(context),
          selectedIndex: selectedIndex,
          pressedIndex: pressedIndex,
          backgroundColors: backgroundColors,
          borderColor: borderColor
        );
      }
      public override void updateRenderObject(BuildContext context,RenderObject renderObject) {
          renderObject = (_RenderSegmentedControl<T>) renderObject;
          ((_RenderSegmentedControl<T>) renderObject).textDirection = Directionality.of(context);
          ((_RenderSegmentedControl<T>) renderObject).selectedIndex = selectedIndex;
          ((_RenderSegmentedControl<T>) renderObject).pressedIndex = pressedIndex;
          ((_RenderSegmentedControl<T>) renderObject).backgroundColors = backgroundColors;
          ((_RenderSegmentedControl<T>) renderObject).borderColor = borderColor;
              
      }
    }

    class _SegmentedControlContainerBoxParentData : ContainerBoxParentData<RenderBox> {
        public RRect surroundingRect;
    }

    public delegate RenderBox _NextChild(RenderBox child);

    class _RenderSegmentedControl<T> : RenderBoxContainerDefaultsMixinContainerRenderObjectMixinRenderBox<RenderBox,
            ContainerBoxParentData<RenderBox>> {
        public _RenderSegmentedControl(
            int? selectedIndex = null,
            int? pressedIndex = null,
            TextDirection? textDirection = null,
            List<Color> backgroundColors = null,
            Color borderColor =  null
        ) {
            D.assert(textDirection != null);
            _textDirection = textDirection;
            _selectedIndex = selectedIndex;
            _pressedIndex = pressedIndex;
            _backgroundColors = backgroundColors;
            _borderColor = borderColor;
        }

            public int? selectedIndex {
               get {return _selectedIndex; }
               set {
                   if (_selectedIndex == value) {
                       return;
                   }
                   _selectedIndex = value;
                   markNeedsPaint();
               }
           }
           int? _selectedIndex;

           public int? pressedIndex {
               get {
                   return _pressedIndex;
               }
               set {
                   if (_pressedIndex == value) {
                       return;
                   }
                   _pressedIndex = value;
                   markNeedsPaint();
               }
           }
           int? _pressedIndex;

           public TextDirection? textDirection {
               get {
                   return _textDirection;
               }
               set {
                   if (_textDirection == value) {
                       return;
                   }
                   _textDirection = value;
                   markNeedsLayout();
               }
           }
           TextDirection? _textDirection;


           public List<Color> backgroundColors {
               get {
                   return _backgroundColors;
               }
               set {
                   if (_backgroundColors == value) {
                       return;
                   }
                   _backgroundColors = value;
                   markNeedsPaint();
               }
           }
           List<Color> _backgroundColors;


           public Color borderColor {
               get {
                   return _borderColor;
                   
               }
               set {
                   if (_borderColor == value) {
                       return;
                   }
                   _borderColor = value;
                   markNeedsPaint();
               
               }
           
           }
           Color _borderColor;


           protected internal override float computeMinIntrinsicWidth(float height) {
                RenderBox child = firstChild;
                float minWidth = 0.0f;
                while (child != null) {
                   _SegmentedControlContainerBoxParentData childParentData = child.parentData as _SegmentedControlContainerBoxParentData;
                   float childWidth = child.getMinIntrinsicWidth(height);
                  minWidth = Mathf.Max(minWidth, childWidth);
                  child = childParentData.nextSibling;
                }
                return minWidth * childCount;
           }

           protected internal override float computeMaxIntrinsicWidth(float height) {
                RenderBox child = firstChild;
                float maxWidth = 0.0f;
                while (child != null) {
                   _SegmentedControlContainerBoxParentData childParentData = child.parentData as _SegmentedControlContainerBoxParentData;
                   float childWidth = child.getMaxIntrinsicWidth(height);
                  maxWidth =  Mathf.Max(maxWidth, childWidth);
                  child = childParentData.nextSibling;
                }
                return maxWidth * childCount;
          }

           protected internal override float computeMinIntrinsicHeight(float width) {
                RenderBox child = firstChild;
                float minHeight = 0.0f;
                while (child != null) {
                   _SegmentedControlContainerBoxParentData childParentData = child.parentData as _SegmentedControlContainerBoxParentData;
                   float childHeight = child.getMinIntrinsicHeight(width);
                  minHeight =  Mathf.Max(minHeight, childHeight);
                  child = childParentData.nextSibling;
                }
                return minHeight;
           }
           protected internal override float computeMaxIntrinsicHeight(float width) {
                RenderBox child = firstChild;
                float maxHeight = 0.0f;
                while (child != null) {
                   _SegmentedControlContainerBoxParentData childParentData = child.parentData as _SegmentedControlContainerBoxParentData;
                   float childHeight = child.getMaxIntrinsicHeight(width);
                  maxHeight =  Mathf.Max(maxHeight, childHeight);
                  child = childParentData.nextSibling;
                }
                return maxHeight;
           }

          public override float? computeDistanceToActualBaseline(TextBaseline baseline) {
            return defaultComputeDistanceToHighestActualBaseline(baseline);
          }

          public override void setupParentData(RenderObject child) {
              child = (RenderBox) child;
            if (!(child.parentData is _SegmentedControlContainerBoxParentData)) {
              child.parentData = new _SegmentedControlContainerBoxParentData();
            }
          }

          void _layoutRects(_NextChild nextChild, RenderBox leftChild, RenderBox rightChild) {
            RenderBox child = leftChild;
            float start = 0.0f;
            while (child != null) {
               _SegmentedControlContainerBoxParentData childParentData = child.parentData as _SegmentedControlContainerBoxParentData;
               Offset childOffset = new Offset(start, 0.0f);
              childParentData.offset = childOffset;
              Rect childRect = Rect.fromLTWH(start, 0.0f, child.size.width, child.size.height);
              RRect rChildRect = null;
              if (child == leftChild) {
                rChildRect = RRect.fromRectAndCorners(childRect, topLeft: Radius.circular(3.0f),
                    bottomLeft: Radius.circular(3.0f));
              } else if (child == rightChild) {
                rChildRect = RRect.fromRectAndCorners(childRect, topRight: Radius.circular(3.0f),
                    bottomRight: Radius.circular(3.0f));
              } else {
                rChildRect = RRect.fromRectAndCorners(childRect,topRight:Radius.zero);
              }
              childParentData.surroundingRect = rChildRect;
              start += child.size.width;
              child = nextChild(child);
            }
          }
          protected override void performLayout() {
             BoxConstraints constraints = this.constraints;
            float maxHeight = CupertinoSegmentedControlsUtils._kMinSegmentedControlHeight;

            float childWidth = constraints.minWidth / childCount;
            foreach ( RenderBox child in getChildrenAsList()) {
              childWidth =  Mathf.Max(childWidth, child.getMaxIntrinsicWidth(float.PositiveInfinity));
            }
            childWidth = Mathf.Min(childWidth, constraints.maxWidth / childCount);

            RenderBox child1 = firstChild;
            while (child1 != null) {
               float boxHeight = child1.getMaxIntrinsicHeight(childWidth);
              maxHeight =  Mathf.Max(maxHeight, boxHeight);
              child1 = childAfter(child1);
            }

            constraints.constrainHeight(maxHeight);

             BoxConstraints childConstraints = BoxConstraints.tightFor(
              width: childWidth,
              height: maxHeight
            );

            child1 = firstChild;
            while (child1 != null) {
              child1.layout(childConstraints, parentUsesSize: true);
              child1 = childAfter(child1);
            }

            switch (textDirection) {
              case TextDirection.rtl:
                _layoutRects(
                  childBefore,
                  lastChild,
                  firstChild
                );
                break;
              case TextDirection.ltr:
                _layoutRects(
                  childAfter,
                  firstChild,
                  lastChild
                );
                break;
            }

            size = constraints.constrain(new Size(childWidth * childCount, maxHeight));
          }
          public override void paint(PaintingContext context, Offset offset) {
            RenderBox child = firstChild;
            int index = 0;
            while (child != null) {
              _paintChild(context, offset, child, index);
              child = childAfter(child);
              index += 1;
            }
          }

          void _paintChild(PaintingContext context, Offset offset, RenderBox child, int childIndex) {
            D.assert(child != null);

             _SegmentedControlContainerBoxParentData childParentData = child.parentData as _SegmentedControlContainerBoxParentData;

            context.canvas.drawRRect(
              childParentData.surroundingRect.shift(offset),
              new Paint(){
                color = backgroundColors[childIndex],
                style = PaintingStyle.fill}
            );
            context.canvas.drawRRect(
              childParentData.surroundingRect.shift(offset),
              new Paint(){
                color = borderColor,
                strokeWidth = 1.0f,
                style = PaintingStyle.stroke}
            );

            context.paintChild(child, childParentData.offset + offset);
          }

          protected override bool hitTestChildren(BoxHitTestResult result, Offset position = null ) {
            D.assert(position != null);
            RenderBox child = lastChild;
            while (child != null) {
               _SegmentedControlContainerBoxParentData childParentData = child.parentData as _SegmentedControlContainerBoxParentData;
              if (childParentData.surroundingRect.contains(position)) {
                 Offset center = (Offset.zero & child.size).center;
                return result.addWithRawTransform(
                  transform: MatrixUtils.forceToPoint(center),
                  position: center,
                  hitTest: (BoxHitTestResult result1, Offset position1) =>{
                    D.assert(position1 == center);
                    return child.hitTest(result1, position: center);
                  }
                );
              }
              child = childParentData.previousSibling;
            }
            return false;
          }
}

    
    



}