Viewport constructor

Viewport({Key key, AxisDirection axisDirection: AxisDirection.down, AxisDirection crossAxisDirection, double anchor: 0.0, @required ViewportOffset offset, Key center, double cacheExtent, List<Widget> slivers: const [] })

Creates a widget that is bigger on the inside.

The viewport listens to the offset, which means you do not need to rebuild this widget when the offset changes.

The offset argument must not be null.

Implementation 

Viewport({
  Key key,
  this.axisDirection = AxisDirection.down,
  this.crossAxisDirection,
  this.anchor = 0.0,
  @required this.offset,
  this.center,
  this.cacheExtent,
  List<Widget> slivers = const <Widget>[],
}) : assert(offset != null),
     assert(slivers != null),
     assert(center == null || slivers.where((Widget child) => child.key == center).length == 1),
     super(key: key, children: slivers);