AutoLayoutChild({AutoLayoutRect rect, @required Widget child })

Creates a widget that provides constraints for a child of an AutoLayout widget.

The object identity of the rect argument must be unique among children of a given AutoLayout widget.

Source 

AutoLayoutChild({
  AutoLayoutRect rect,
  @required Widget child
}) : rect = rect,
     super(key: rect != null ? new ObjectKey(rect) : null, child: child);