CGFloat lastContentOffset;  //ScoreView 滑动位置 -(void)scrollViewWillBeginDragging:(UIScrollView*)scrollView{     lastContentOffset = scrollView.contentOffset.y;}-( void )scrollViewDidScroll:( UIScrollView *)scrollView {   if (scrollView. contentOffset.y < lastContentOffset )   {       //向上，隐藏导航栏      [ self.navigationController setNavigationBarHidden : NO animated : YES ];    }      else if (scrollView. contentOffset.y > lastContentOffset )    {       //向下       [ self.navigationController setNavigationBarHidden : YES animated : YES ];     }}