title: Flutter adding Draggable Scrollbar to a CustomScrollView? It keeps giving me 'The argument type CustomScrollView can't be assigned to BoxScrollView'
body: <p>A Simple example would be:</p>
  
  <pre><code>Scaffold(
            floatingActionButton: _fab(),
            floatingActionButtonLocation: _fabLocation(),
            body: Scrollbar(
              child: CustomScrollView(
                slivers: &lt;Widget&gt;[
                  SliverAppBar(
                    automaticallyImplyLeading: false,
                    leading: null,
                    backgroundColor: Theme.of(context).colorScheme.secondary,
                    title: AutoSizeText(
                      _catalogSearchRatio,
                      style: Theme.of(context).textTheme.title.copyWith(
                          color: Theme.of(context).colorScheme.onSecondary),
                    ),
                    floating: true,
                    pinned: false,
                  ),
                  SliverFixedExtentList(
                    itemExtent: 90.0,
                    delegate: SliverChildBuilderDelegate((context, index) {
                      return Padding(
                        padding: const EdgeInsets.symmetric(
                            horizontal: 5.0, vertical: 5.0),
                        child: CatalogItems.medidaGroups
                                .contains(_itemsCatalogDisplay[index].group)
                            ? _medidasCard(
                                index, _itemsCatalogDisplay, _catalogSearchQuery)
                            : _catalogCard(index, _itemsCatalogDisplay,
                                _catalogSearchQuery, _cartItems, _filteredGroups),
                      );
                    }, childCount: itemsCatalogDisplayLength),
                  ),
                ],
                controller: _catalogScrollController,
              ),
            ),
          );
  </code></pre>
  
  <p>In the above example, a Scrollbar can be used and that's fine. BUT you can't drag the scrollbar. So I am using a package called <a href="https://pub.dev/packages/draggable_scrollbar" rel="nofollow noreferrer"><strong>draggable_scrollbar</strong></a> which lets me drag the scrollbar. However, I can't seem to replace the scrollbar I have in the example because it gives me the can't be assigned to BoxScrollView error.
  It works if it's just a <strong>Listview</strong> or a <strong>Listview.builder</strong> or even a <strong>GridView</strong></p>