childCount property

int childCount

The maximum number of children that can be provided to RenderListWheelViewport.

If non-null, the children will have index in the range 0, childCount - 1.

If null, then there's no explicit limits to the range of the children except that it has to be contiguous. If childExistsAt for a certain index returns false, that index is already past the limit.

Implementation 

int get childCount;