RenderViewportBase<ParentDataClass extends ContainerParentDataMixin<RenderSliver>> constructor

RenderViewportBase<ParentDataClass extends ContainerParentDataMixin<RenderSliver>>({AxisDirection axisDirection: AxisDirection.down, @required AxisDirection crossAxisDirection, @required ViewportOffset offset, double cacheExtent })

Initializes fields for subclasses.

Implementation 

RenderViewportBase({
  AxisDirection axisDirection = AxisDirection.down,
  @required AxisDirection crossAxisDirection,
  @required ViewportOffset offset,
  double cacheExtent,
}) : assert(axisDirection != null),
     assert(crossAxisDirection != null),
     assert(offset != null),
     assert(axisDirectionToAxis(axisDirection) != axisDirectionToAxis(crossAxisDirection)),
     _axisDirection = axisDirection,
     _crossAxisDirection = crossAxisDirection,
     _offset = offset,
     _cacheExtent = cacheExtent ?? RenderAbstractViewport.defaultCacheExtent;