fix background

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

         }
 
         public readonly Animation<Offset> _primaryPositionAnimation;
-
-
         public readonly Widget child;
 
         public override Widget build(BuildContext context) {
         void _handleDragEnd(DragEndDetails details) {
             D.assert(mounted);
             D.assert(_backGestureController != null);
-            _backGestureController.dragEnd(_convertToLogical(details.velocity.pixelsPerSecond.dx / context.size.width) ?? 0);
+            _backGestureController.dragEnd(_convertToLogical(details.velocity.pixelsPerSecond.dx / context.size.width) ?? 0.0f);
             _backGestureController = null;
         }
 
                 fit: StackFit.passthrough,
                 children: new List<Widget> {
                     widget.child,
-                    new Positioned(
-                        left: 0.0f,
+                    new PositionedDirectional(
+                        start: 0.0f,
                         width: dragAreaWidth,
                         top: 0.0f,
                         bottom: 0.0f,
                         )
-                    )
+                    ),
                 }
             );
         }

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

     }
 
     public class FixedExtentMetrics : FixedScrollMetrics, IFixedExtentMetrics {
-        /*public FixedExtentMetrics(
-            float? minScrollExtent = null,
-            float? maxScrollExtent = null,
-            float? pixels = null,
-            float? viewportDimension = null,
-            AxisDirection axisDirection = AxisDirection.down,
-            int? itemIndex = null
-        ) : base(
-            minScrollExtent: minScrollExtent ?? 0.0f,
-            maxScrollExtent: maxScrollExtent ?? 0.0f,
-            pixels: pixels ?? 0.0f,
-            viewportDimension: viewportDimension ?? 0.0f,
-            axisDirection: axisDirection
-        ) {
-            this.itemIndex = itemIndex ?? 0;
-        }*/
         public FixedExtentMetrics(
             float minScrollExtent ,
             float maxScrollExtent,