wrapVerticalDirection property
Determines the order to lay children out vertically and how to interpret
start and end in the vertical direction.
If the wrapDirection is Axis.vertical, this controls which order children are painted in (down or up), the meaning of the wrapAlignment property's WrapAlignment.start and WrapAlignment.end values.
If the wrapDirection is Axis.vertical, and either the wrapAlignment is either WrapAlignment.start or WrapAlignment.end, or there's more than one child, then the wrapVerticalDirection must not be null.
If the wrapDirection is Axis.horizontal, this controls the order in which runs are positioned, the meaning of the wrapRunAlignment property's WrapAlignment.start and WrapAlignment.end values, as well as the wrapCrossAxisAlignment property's WrapCrossAlignment.start and WrapCrossAlignment.end values.
If the wrapDirection is Axis.horizontal, and either the wrapRunAlignment is either WrapAlignment.start or WrapAlignment.end, the wrapCrossAxisAlignment is either WrapCrossAlignment.start or WrapCrossAlignment.end, or there's more than one child, then the wrapVerticalDirection must not be null.
Implementation
final VerticalDirection wrapVerticalDirection;