cacheExtent property Null safety
How many pixels the sliver has consumed in the SliverConstraints.remainingCacheExtent.
This value should be equal to or larger than the layoutExtent because the sliver always consumes at least the layoutExtent from the SliverConstraints.remainingCacheExtent and possibly more if it falls into the cache area of the viewport.
- RenderViewport.cacheExtent for a description of a viewport's cache area.
final double cacheExtent