cacheExtend property
The viewport has an area before and after the visible area to cache items
that are about to become visible when the user scrolls.
Items that fall in this cache area are laid out even though they are
not (yet) visible on screen. The cacheExtent
describes how many pixels
the cache area extends before the leading edge and after the trailing
edge of the viewport.
The total extent, which the viewport will try to cover with children,
is cacheExtent
before the leading edge + extent of the
main axis + cacheExtent
after the trailing edge.
Implementation
final double cacheExtend;