判断UISrollview的滑动方向

-(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {    historyY = scrollView.contentOffset.y;}-(void)scrollViewDidScroll:(UIScrollView *)scrollView {         if (scrollView.contentOffset.y<historyY) {        NSLog(@"down");         } else if (scrollView.contentOffset.y>historyY) {        NSLog(@"up");           }}