fix picker

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

                     _onSelectedItemChange(index); 
                 },
                 itemBuilder: (BuildContext context, int index) => {
-                    
-                    rangeStart.AddDays(index);
+                    rangeStart = rangeStart.AddDays(index);
                     
                     var rangeEnd  = rangeStart.AddDays(1);
                     
                         return null; 
-                    if (widget.maximumDate?.CompareTo(rangeStart) > 0) 
+                    if (widget.maximumDate?.CompareTo(rangeStart) < 0) 
                         return null;
                     
                     string dateText = rangeStart == new DateTime(now.Year, now.Month, now.Day)
         DateTime _lastDayInMonth(int year, int month) {
             //new DateTime(year, month + 1, 0);
             var date = new DateTime(year,month,1);
-            date.AddMonths(1);
-            date.Subtract(new TimeSpan(1, 0, 0, 0));
+            date = date.AddMonths(1);
+            date = date.Subtract(new TimeSpan(1, 0, 0, 0));
             return date;
         }
 

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

     public class CupertinoPicker : StatefulWidget {
         public CupertinoPicker(
             List<Widget> children,
+            float itemExtent,
             Key key = null,
             float? diameterRatio = null,
             Color backgroundColor = null,
             FixedExtentScrollController scrollController = null,
             float? squeeze = null,
-            float? itemExtent = null,
             ValueChanged<int> onSelectedItemChanged = null,
             bool looping = false
         ) : base(key: key) {
             D.assert(diameterRatio > 0.0f, ()=>RenderListWheelViewport.diameterRatioZeroMessage);
             D.assert(magnification > 0);
-            D.assert(itemExtent != null);
             D.assert(itemExtent > 0);
             D.assert(squeeze > 0);
             this.diameterRatio = diameterRatio;
         }
 
         public CupertinoPicker(
+            float itemExtent,
             Key key = null,
             float? diameterRatio = null,
             Color backgroundColor = null,
             FixedExtentScrollController scrollController = null,
             float? squeeze = null,
-            float? itemExtent = null,
+            
             ValueChanged<int> onSelectedItemChanged = null,
             IndexedWidgetBuilder itemBuilder = null,
             int? childCount = null
             D.assert(itemBuilder != null);
             D.assert(diameterRatio > 0.0f,()=> RenderListWheelViewport.diameterRatioZeroMessage);
             D.assert(magnification > 0);
-            D.assert(itemExtent != null);
             D.assert(itemExtent > 0);
             D.assert(squeeze > 0);
             this.diameterRatio = diameterRatio;
         public readonly bool useMagnifier;
         public readonly float magnification;
         public readonly FixedExtentScrollController scrollController;
-        public readonly float? itemExtent;
+        public readonly float itemExtent;
         public readonly ValueChanged<int> onSelectedItemChanged;
         public ListWheelChildDelegate childDelegate;
         public readonly float? squeeze;
         }
 
         public override void didUpdateWidget(StatefulWidget oldWidget) {
+            oldWidget = (CupertinoPicker) oldWidget;
             if (widget.scrollController != null && ((CupertinoPicker) oldWidget).scrollController == null) {
                 _controller = null;
             }
                         child: new ListWheelScrollView(
                             controller: widget.scrollController ?? _controller,
                             physics: new FixedExtentScrollPhysics(), 
-                            diameterRatio: widget.diameterRatio ?? CupertinoPickerUtils._kDefaultDiameterRatio,
+                            diameterRatio: widget.diameterRatio ?? RenderListWheelViewport.defaultDiameterRatio ,
-                            itemExtent: widget.itemExtent ?? 1f,
+                            itemExtent: widget.itemExtent ,
                             squeeze: widget.squeeze ?? CupertinoPickerUtils._kSqueeze,
                             onSelectedItemChanged: _handleSelectedItemChanged,
                             childDelegate: widget.childDelegate

com.unity.uiwidgets/Runtime/painting/matrix_utils.cs

             return (e > f) ? e : f;
         }
 
-        static Matrix4 createCylindricalProjectionTransform(
+        public static Matrix4 createCylindricalProjectionTransform(
             float radius,
             float angle,
             float perspective = 0.001f,

com.unity.uiwidgets/Runtime/rendering/layer.cs

 
             var totalOffset = offset + layerOffset;
             if (totalOffset != Offset.zero) {
-                _lastEffectiveTransform = Matrix4.translationValues(totalOffset.dx, totalOffset.dy, 0);
+                _lastEffectiveTransform = Matrix4.translationValues(totalOffset.dx, totalOffset.dy, 0.0f);
                 _lastEffectiveTransform.multiply(transform);
             }
 
             _lastOffset = offset + layerOffset;
             if (_lastOffset != Offset.zero) {
                 engineLayer = builder.pushTransform(
-                     Matrix4.translationValues(_lastOffset.dx, _lastOffset.dy,0)
-                    ._m4storage,
+                     Matrix4.translationValues(_lastOffset.dx, _lastOffset.dy,0.0f).storage,
                     oldLayer: engineLayer as TransformEngineLayer);
             }
 
                 return null;
             }
 
-            Matrix4 result = Matrix4.translationValues(-_lastOffset.dx, -_lastOffset.dy,0 );
+            Matrix4 result = Matrix4.translationValues(-_lastOffset.dx, -_lastOffset.dy,0.0f );
             result.multiply(_lastTransform);
             return result;
         }
             _establishTransform();
             if (_lastTransform != null) {
                 engineLayer = builder.pushTransform(
-                    _lastTransform._m4storage,
+                    _lastTransform.storage,
                     oldLayer: engineLayer as TransformEngineLayer);
                 addChildrenToScene(builder);
                 builder.pop();
                 _lastOffset = null;
-                var matrix = Matrix4.translationValues(unlinkedOffset.dx, unlinkedOffset.dy, 0);
+                var matrix = Matrix4.translationValues(unlinkedOffset.dx, unlinkedOffset.dy, 0.0f);
-                    matrix._m4storage,
+                    matrix.storage,
                     oldLayer: engineLayer as TransformEngineLayer);
                 addChildrenToScene(builder);
                 builder.pop();
                 transform.multiply(_lastTransform);
             }
             else {
-                transform.multiply(Matrix4.translationValues(unlinkedOffset.dx, unlinkedOffset.dy, 0));
+                transform.multiply(Matrix4.translationValues(unlinkedOffset.dx, unlinkedOffset.dy, 0.0f));
             }
         }
 

com.unity.uiwidgets/Runtime/rendering/list_wheel_viewport.cs

             var radius = size.height * _diameterRatio / 2.0f;
             var deltaY = radius * Mathf.Sin(angle);
 
-            Matrix4 transform = Matrix4.identity();
-            // Matrix4x4 transform2 = MatrixUtils.createCylindricalProjectionTransform(
-            //     radius: this.size.height * this._diameterRatio / 2.0f,
-            //     angle: angle,
-            //     perspective: this._perspective
-            // );
+            Matrix4 transform = MatrixUtils.createCylindricalProjectionTransform(
+                radius: size.height * _diameterRatio / 2.0f,
+                angle: angle,
+                perspective: _perspective
+            );
-            // Offset offsetToCenter = new Offset(untransformedPaintingCoordinates.dx, -this._topScrollMarginExtent);
+            // Offset that helps painting everything in the center (e.g. angle = 0).
+            Offset offsetToCenter = new Offset(
+                untransformedPaintingCoordinates.dx,
+                -_topScrollMarginExtent
+            );
-            Offset offsetToCenter =
-                new Offset(untransformedPaintingCoordinates.dx, -deltaY - _topScrollMarginExtent);
 
             bool shouldApplyOffCenterDim = overAndUnderCenterOpacity < 1;
             if (useMagnifier || shouldApplyOffCenterDim) {

com.unity.uiwidgets/Runtime/widgets/list_wheel_scroll_view.cs

             if (children.isEmpty()) {
                 return null;
             }
-            return new Container(child: children[Mathf.Abs(index % children.Count)]);
+            return new IndexedSemantics(child: children[Mathf.Abs(index % children.Count)]);
         }
 
         public bool shouldRebuild(ListWheelChildDelegate oldDelegate) {
         public Widget build(BuildContext context, int index) {
             if (childCount == null) {
                 Widget child = builder(context, index);
-                return child == null ? null : new Container(child: child);
+                return child == null ? null : new IndexedSemantics(child: child);
             }
 
             if (index < 0 || index >= childCount) {
-            return new Container(child: builder(context, index));
+            return new IndexedSemantics(child: builder(context, index));
         }
 
         public int trueIndexOf(int index) {
 
     class ListWheelScrollViewUtils {
         public static int _getItemFromOffset(
-            float? offset = null,
-            float? itemExtent = null,
-            float? minScrollExtent = null,
-            float? maxScrollExtent = null
+            float offset ,
+            float itemExtent ,
+            float minScrollExtent ,
+            float maxScrollExtent 
-            var _itemExtent = itemExtent ?? 1.0f;
-            return (_clipOffsetToScrollableRange(offset ?? 0.0f , minScrollExtent ?? 0.0f, maxScrollExtent ?? 0.0f) / _itemExtent).round();
+            return (_clipOffsetToScrollableRange(offset, minScrollExtent, maxScrollExtent) / itemExtent).round();
         }
         public static float _clipOffsetToScrollableRange(
             float offset,
                     () =>
                         "The selectedItem property cannot be read when multiple scroll views are attached to the same FixedExtentScrollController."
                 );
-                _FixedExtentScrollPosition position = (_FixedExtentScrollPosition) this.position;
+                _FixedExtentScrollPosition position = (_FixedExtentScrollPosition) this.position; 
                 return position.itemIndex;
             }
         }
-            TimeSpan? duration = null,
-            Curve curve = null
+            TimeSpan duration,
+            Curve curve
+            
-                    duration: duration ?? new TimeSpan(0,0,0,0,0),
+                    duration: duration,
-
             return Future.wait<object>(futures);
         }
 
     public interface IFixedExtentMetrics {
         int itemIndex { set; get; }
 
+        /*FixedExtentMetrics copyWith(
+            float? minScrollExtent = null,
+            float? maxScrollExtent = null,
+            float? pixels = null,
+            float? viewportDimension = null,
+            AxisDirection? axisDirection = null,
+            int? itemIndex = null
+        );*/
+        
         FixedExtentMetrics copyWith(
             float? minScrollExtent = null,
             float? maxScrollExtent = null,
     }
 
     public class FixedExtentMetrics : FixedScrollMetrics, IFixedExtentMetrics {
-        public FixedExtentMetrics(
+        /*public FixedExtentMetrics(
             float? minScrollExtent = null,
             float? maxScrollExtent = null,
             float? pixels = null,
             axisDirection: axisDirection
         ) {
             this.itemIndex = itemIndex ?? 0;
+        }*/
+        public FixedExtentMetrics(
+            float minScrollExtent ,
+            float maxScrollExtent,
+            float pixels ,
+            float viewportDimension ,
+            AxisDirection axisDirection ,
+            int itemIndex 
+        ) : base(
+            minScrollExtent: minScrollExtent ,
+            maxScrollExtent: maxScrollExtent ,
+            pixels: pixels ,
+            viewportDimension: viewportDimension ,
+            axisDirection: axisDirection
+        ) {
+            this.itemIndex = itemIndex;
         }
 
         public int itemIndex { get; set; }
         ) : base(
             physics: physics,
             context: context,
-            initialPixels: _getItemExtentFromScrollContext(context) * initialItem,
+            initialPixels: _getItemExtentFromScrollContext(context) * (initialItem ?? 0.0f),
             keepScrollOffset: keepScrollOffset,
             oldPosition: oldPosition,
             debugLabel: debugLabel
 
         static float _getItemExtentFromScrollContext(ScrollContext context) {
             _FixedExtentScrollableState scrollable = (_FixedExtentScrollableState) context;
-            return scrollable.itemExtent ?? 0.0f;
+            return scrollable.itemExtent;
         }
 
         public float itemExtent {
 
     class _FixedExtentScrollable : Scrollable {
         public _FixedExtentScrollable(
+            float itemExtent,
-            ScrollPhysics physics = null,
-            float? itemExtent = null,
+            ScrollPhysics physics = null, 
+            
         ) : base(
             key: key,
             axisDirection: axisDirection,
             this.itemExtent = itemExtent;
         }
 
-        public readonly float? itemExtent;
+        public readonly float itemExtent;
 
         public override State createState() {
             return new _FixedExtentScrollableState();
     class _FixedExtentScrollableState : ScrollableState {
-        public float? itemExtent {
+        public float itemExtent {
             get {
                 _FixedExtentScrollable actualWidget = (_FixedExtentScrollable) widget;
                 return actualWidget.itemExtent;
     public class ListWheelScrollView : StatefulWidget {
         public ListWheelScrollView(
             List<Widget> children,
+            float itemExtent,
             Key key = null,
             ScrollController controller = null,
             ScrollPhysics physics = null,
             bool useMagnifier = false,
             float magnification = 1.0f,
             float overAndUnderCenterOpacity = 1.0f,
-            float? itemExtent = null,
             float squeeze = 1.0f,
             ValueChanged<int> onSelectedItemChanged = null,
             bool clipToSize = true,
         }
 
         public ListWheelScrollView (
+            float itemExtent,
             Key key = null,
             ScrollController controller = null,
             ScrollPhysics physics = null,
             bool useMagnifier = false,
             float magnification = 1.0f,
-            float? itemExtent = null,
             float squeeze = 1.0f,
             ValueChanged<int> onSelectedItemChanged = null,
             float overAndUnderCenterOpacity = 1.0f,
         public readonly float offAxisFraction;
         public readonly bool useMagnifier;
         public readonly float magnification;
-        public readonly float? itemExtent;
+        public readonly float itemExtent;
         public readonly float overAndUnderCenterOpacity;
         public readonly float squeeze;
         public readonly ValueChanged<int> onSelectedItemChanged;

com.unity.uiwidgets/Runtime/widgets/scrollable.cs

             if (widget.physics != null) {
                 _physics = widget.physics.applyTo(_physics);
             }
-
             ScrollController controller = widget.controller;
             ScrollPosition oldPosition = position;
             if (oldPosition != null) {
                 });
             }
 
-            _position = controller == null
-                ? null
-                : controller.createScrollPosition(_physics, this, oldPosition);
-            _position = _position
-                             ?? new ScrollPositionWithSingleContext(physics: _physics, context: this,
-                                 oldPosition: oldPosition);
+            if (controller == null) {
+                _position = new ScrollPositionWithSingleContext(physics: _physics, context: this, oldPosition: oldPosition);
+                
+            }
+            else {
+                _position = controller?.createScrollPosition(_physics, this, oldPosition)
+                            ?? new ScrollPositionWithSingleContext(physics: _physics, context: this, oldPosition: oldPosition);
+            }
+
             D.assert(position != null);
             if (controller != null) {
                 controller.attach(position);