PageViewport({double startOffset: 0.0, Axis mainAxis: Axis.vertical, ViewportAnchor anchor: ViewportAnchor.start, bool itemsWrap: false, Iterable<Widget> children: const [] })

Creates a virtual viewport that displays a single child at a time.

The mainAxis and anchor arguments must not be null.

Source 

PageViewport({
  double startOffset: 0.0,
  Axis mainAxis: Axis.vertical,
  ViewportAnchor anchor: ViewportAnchor.start,
  bool itemsWrap: false,
  this.children: const <Widget>[],
}) : super(
  startOffset,
  mainAxis,
  anchor,
  itemsWrap
);