1. override
double getMaxIntrinsicHeight(double width, int childCount)

Returns the smallest height beyond which increasing the height never decreases the preferred width.

Override this to provide a more efficient or more correct solution. The default implementation actually instantiates a grid specification and measures the grid at the given height and child count.

For more details on implementing this method, see RenderBox.computeMaxIntrinsicHeight.

Source 

@override
double getMaxIntrinsicHeight(double width, int childCount) {
  // TODO(ianh): Strictly, this should examine the children.
  return 0.0;
}