tableview的headerview不随着移动

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    CGFloat sectionHeaderHeight = 40;

    if  (scrollView.contentOffset.y<=sectionHeaderHeight&&scrollView.contentOffset.y>=0) 

   {

        scrollView.contentInset = UIEdgeInsetsMake(-scrollView.contentOffset.y, 0, 0, 0);

    } 

    else if (scrollView.contentOffset.y>=sectionHeaderHeight)

    {

        scrollView.contentInset = UIEdgeInsetsMake(-sectionHeaderHeight, 0, 0, 0);

    }

}