RenderAligningShiftedBox({FractionalOffset alignment: FractionalOffset.center, RenderBox child })

Initializes member variables for subclasses.

The alignment argument must not be null.

Source 

RenderAligningShiftedBox({
  FractionalOffset alignment: FractionalOffset.center,
  RenderBox child
}) : _alignment = alignment, super(child) {
  assert(alignment != null && alignment.dx != null && alignment.dy != null);
}