设置上拉隐藏下拉显示导航栏

//设置上拉隐藏下拉显示导航栏
-(void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{
    if (velocity.y > 0) {
        [self.navigationController setNavigationBarHidden:YES animated:YES];
    }else{
        [self.navigationController setNavigationBarHidden:NO animated:YES];
    }
}