ListViewport({ExtentsChangedCallback onExtentsChanged, double scrollOffset: 0.0, Axis mainAxis: Axis.vertical, ViewportAnchor anchor: ViewportAnchor.start, @required double itemExtent, bool itemsWrap: false, EdgeInsets padding, Iterable<Widget> children: const [] })

Creates a virtual viewport onto a list of equally sized children.

The mainAxis, anchor, and itemExtent arguments must not be null.

Source 

ListViewport({
  ExtentsChangedCallback onExtentsChanged,
  double scrollOffset: 0.0,
  Axis mainAxis: Axis.vertical,
  ViewportAnchor anchor: ViewportAnchor.start,
  @required double itemExtent,
  bool itemsWrap: false,
  EdgeInsets padding,
  this.children: const <Widget>[],
}) : super(
  onExtentsChanged,
  scrollOffset,
  mainAxis,
  anchor,
  itemExtent,
  itemsWrap,
  padding
);