double stepHeight

If non-null, force the child's height to be a multiple of this value.

Source 

double get stepHeight => _stepHeight;
void stepHeight=(double newStepHeight)

Source 

set stepHeight(double newStepHeight) {
  if (newStepHeight == _stepHeight)
    return;
  _stepHeight = newStepHeight;
  markNeedsLayout();
}