docs: private int calcItemWidth(RecyclerView rvCategories) {
          if (itemWidth == null || itemWidth == 0) {
              for (int i = 0; i < rvCategories.getChildCount(); i++) {
                  itemWidth = rvCategories.getChildAt(i).getWidth();
                  if (itemWidth != 0) {
                      break;
                  }
              }
          }
          // in case of call before view was created
          if (itemWidth == null) {
              itemWidth = 0;
          }
          return itemWidth;
      }