UIScrollView 滚动方向判断

网上大部分方法判断不准确，缓慢上下拖动判断不准确；请使用如下方法判断：

CGFloat lastContentOffset;

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {

    NSLog(@"scrollViewWillBeginDragging = %f", scrollView.contentOffset.y);

    lastContentOffset = scrollView.contentOffset.y;

}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    if (lastContentOffset > scrollView.contentOffset.y) {

        NSLog(@"下滑");

    } else if (lastContentOffset < scrollView.contentOffset.y){

        NSLog(@"上滑");

    }     

    lastContentOffset = scrollView.contentOffset.y;

}