itemExtent property

double itemExtent

The size of the children along the main axis. Children RenderBoxes will be given the BoxConstraints of this exact size.

Must not be null and must be positive.

Implementation 

double get itemExtent => _itemExtent;
void itemExtent= (double value)

Implementation 

set itemExtent(double value) {
  assert(value != null);
  assert(value > 0);
  if (value == _itemExtent)
    return;
  _itemExtent = value;
  markNeedsLayout();
}