Usage

class BeerListView extends StatefulWidget {
  @override
  _BeerListViewState createState() => _BeerListViewState();
}

class _BeerListViewState extends State<BeerListView> {
  static const _pageSize = 20;

  final PagingController<int, BeerSummary> _pagingController =
      PagingController(firstPageKey: 0);

  @override
  void initState() {
    _pagingController.addPageRequestListener((pageKey) {
      _fetchPage(pageKey);
    });
    super.initState();
  }

  Future<void> _fetchPage(int pageKey) async {
    try {
      final newItems = await RemoteApi.getBeerList(pageKey, _pageSize);
      final isLastPage = newItems.length < _pageSize;
      if (isLastPage) {
        _pagingController.appendLastPage(newItems);
      } else {
        final nextPageKey = pageKey + newItems.length;
        _pagingController.appendPage(newItems, nextPageKey);
      }
    } catch (error) {
      _pagingController.error = error;
    }
  }

  @override
  Widget build(BuildContext context) => 
      // Don't worry about displaying progress or error indicators on screen; the 
      // package takes care of that. If you want to customize them, use the 
      // [PagedChildBuilderDelegate] properties.
      PagedListView<int, BeerSummary>(
        pagingController: _pagingController,
        builderDelegate: PagedChildBuilderDelegate<BeerSummary>(
          singleitemBuilder: (context, item, index) => BeerListItem(
            beer: item,
          ),
        ),
      );

  @override
  void dispose() {
    _pagingController.dispose();
    super.dispose();
  }
}

class BeerSliverGrid extends StatefulWidget {
  @override
  _BeerSliverGridState createState() => _BeerSliverGridState();
}

class _BeerSliverGridState extends State<BeerSliverGrid> {
  final BeerListingBloc _bloc = BeerListingBloc();
  final PagingController<int, BeerSummary> _pagingController =
      PagingController(firstPageKey: 1);
  late StreamSubscription _blocListingStateSubscription;

  @override
  void initState() {
    _pagingController.addPageRequestListener((pageKey) {
      _bloc.onPageRequestSink.add(pageKey);
    });

    // We could've used StreamBuilder, but that would unnecessarily recreate
    // the entire [PagedSliverGrid] every time the state changes.
    // Instead, handling the subscription ourselves and updating only the
    // _pagingController is more efficient.
    _blocListingStateSubscription =
        _bloc.onNewListingState.listen((listingState) {
      _pagingController.value = PagingState(
        nextPageKey: listingState.nextPageKey,
        error: listingState.error,
        itemList: listingState.itemList,
      );
    });
    super.initState();
  }

  @override
  Widget build(BuildContext context) => CustomScrollView(
        slivers: <Widget>[
          BeerSearchInputSliver(
            onChanged: (searchTerm) => _bloc.onSearchInputChangedSink.add(
              searchTerm,
            ),
          ),
          PagedSliverGrid<int, BeerSummary>(
            pagingController: _pagingController,
            gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
              childAspectRatio: 100 / 150,
              crossAxisSpacing: 10,
              mainAxisSpacing: 10,
              crossAxisCount: 3,
            ),
            builderDelegate: PagedChildBuilderDelegate<BeerSummary>(
              singleitemBuilder: (context, item, index) => CachedNetworkImage(
                imageUrl: item.imageUrl,
              ),
            ),
          ),
        ],
      );

  @override
  void dispose() {
    _pagingController.dispose();
    _blocListingStateSubscription.cancel();
    _bloc.dispose();
    super.dispose();
  }
}