代码片段：UITableView的plain样式下，取消区头停滞效果

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat sectionHeaderHeight = 30;
    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);
    }
}