noo/lib/widgets/sticky_header_delegate.dart

import 'package:flutter/material.dart';

/// Wraps [child] as a sliver that pins to the top of the scroll view when
/// used with `SliverPersistentHeader(pinned: true, ...)`, or scrolls away
/// normally with `pinned: false`. [height] must match the child's actual
/// rendered height - Flutter's sliver protocol needs an extent up front,
/// not one measured after layout, so callers own getting this right for
/// whatever fixed-height content they pass in.
class StickyHeaderDelegate extends SliverPersistentHeaderDelegate {
  final double height;
  final Widget child;

  const StickyHeaderDelegate({required this.height, required this.child});

  @override
  double get minExtent => height;

  @override
  double get maxExtent => height;

  @override
  Widget build(
    BuildContext context,
    double shrinkOffset,
    bool overlapsContent,
  ) {
    return Material(color: Theme.of(context).colorScheme.surface, child: child);
  }

  @override
  bool shouldRebuild(covariant StickyHeaderDelegate oldDelegate) {
    return oldDelegate.height != height || oldDelegate.child != child;
  }
}