shouldRebuild method
Whether this delegate is meaningfully different from the old delegate.
If this returns false, then the header might not be rebuilt, even though the instance of the delegate changed.
This must return true if oldDelegate
and this object would return
different values for minExtent, maxExtent, snapConfiguration, or
would return a meaningfully different widget tree from build for the
same arguments.
Implementation
@override
bool shouldRebuild(SliverPersistentHeaderDelegate oldDelegate) => false;