tableview 的格式为UITableViewStylePlain，去掉headerview的黏连性

在viewcontroller中实现如下方法
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

if (scrollView == _table) {
CGFloat sectionHeaderHeight = 50;
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);
}

}

}

if ([[[UIDevice currentDevice]systemVersion]floatValue]>=7.0) {
self.edgesForExtendedLayout = UIRectEdgeNone;
}