1. override
double updateExtents({double contentExtent, double containerExtent, double minScrollOffset, double scrollOffset: 0.0 })

Updates either content or container extent (or both)

Returns the new scroll offset of the widget after the change in extent.

The scrollOffset parameter is the scroll offset of the widget before the change in extent.

Source 

@override
double updateExtents({
  double contentExtent,
  double containerExtent,
  double minScrollOffset,
  double scrollOffset: 0.0
}) {
  if (minScrollOffset != null) {
    _minScrollOffset = minScrollOffset;
    assert(minScrollOffset <= maxScrollOffset);
  }
  return super.updateExtents(
    contentExtent: contentExtent,
    containerExtent: containerExtent,
    scrollOffset: scrollOffset
  );
}