tableView内容视图（例如section的headerView）移动

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if (scrollView ==_tableView)
    {
        CGFloat sectionHeaderHeight = 25;
        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);
        }
    }
}