OverscrollIndicator({Key key, Key scrollableKey, ScrollableEdge edge: ScrollableEdge.both, Widget child })

Creates an overscroll indicator.

The child argument must not be null.

Source 

OverscrollIndicator({
  Key key,
  this.scrollableKey,
  this.edge: ScrollableEdge.both,
  this.child
}) : super(key: key) {
  assert(child != null);
  assert(edge != null);
}