In scrollViewWillBeginDragging 滚动视图尚未移动（或注册移动），因此 contentOffset 将为0.自IOS起5你可以改为查看scrollview的 panGestureRecognizer 来确定用户滚动手势的方向和大小。

In scrollViewWillBeginDragging the scroll view has not yet moved (or registered the move) and so contentOffset will by 0. As of IOS 5 you can instead look in the scrollview's panGestureRecognizer to determine the direction and magnitude of the user's scrolling gesture.

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{ 
    CGPoint translation = [scrollView.panGestureRecognizer translationInView:scrollView.superview];

    if(translation.x > 0)
    {
        // react to dragging right
    } else
    {
        // react to dragging left
    }
}