GridViewport({double scrollOffset, GridDelegate delegate, ExtentsChangedCallback onExtentsChanged, Iterable<Widget> children: const [] })

Creates a virtual viewport onto a grid of widgets.

The delegate argument must not be null.

Source 

GridViewport({
  this.scrollOffset,
  this.delegate,
  this.onExtentsChanged,
  this.children: const <Widget>[],
}) {
  assert(delegate != null);
}