判断scrollView、tableView滚动方向（上或下）

float lastContentOffset;
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
    lastContentOffset = scrollView.contentOffset.y;
}
- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView
{
    if (lastContentOffset < scrollView.contentOffset.y){
        NSLog(@"向上滚动");
    }else{
        NSLog(@"向下滚动");}
}