iOS 判断UITableView滑动到哪个分区

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    
    CGFloat y = scrollView.contentOffset.y;
    
    for (NSInteger i = 0; i < self.models.count; i ++) {
        CGFloat offset = [self.tableView rectForSection:i].origin.y;
        CGFloat height = [self.tableView rectForSection:i].size.height;
        if (y >= offset && y <= offset + height) {
            // 滚动到第 i 组
        }
    }
}