rapi_bloc.dart

  void init(TickerProvider ticker) {
    tabController =
        TabController(vsync: ticker, length: rappiCategories.length);

    double offsetFrom = 0.0;
    double offsetTo = 0.0;

    for (int i = 0; i < rappiCategories.length; i++) {
      final category = rappiCategories[i];

      offsetFrom = offsetTo;
      offsetTo = offsetFrom +
          rappiCategories[i].products.length * productHeight +
          categoryHeight;

      tabs.add(RappiTabCategory(
        category: category,
        selected: (i == 0),
        offsetFrom: offsetFrom,
        offsetTo: offsetTo,
      ));
      items.add(RappiItem(category: category));
      for (int j = 0; j < category.products.length; j++) {
        final product = category.products[j];
        items.add(RappiItem(product: product));
      }
    }

    scrollController.addListener(_onScrollListener);
  }