Objective-C代码如下

- (void)scrollViewDidScroll:(UIScrollView *)scrollView

{

//scrollView已经有拖拽手势，直接拿到scrollView的拖拽手势

UIPanGestureRecognizer *pan = scrollView.panGestureRecognizer;

//获取到拖拽的速度 >0 向下拖动 <0 向上拖动

CGFloat velocity = [pan velocityInView:scrollView].y;

if (velocity <- 5) {

//向上拖动，隐藏导航栏

[self.navigationController setNavigationBarHidden:YES animated:YES];

}else if (velocity > 5) {

//向下拖动，显示导航栏

[self.navigationController setNavigationBarHidden:NO animated:YES];

}else if(velocity == 0){

//停止拖拽

}

}

swift代码如下

func scrollViewDidScroll(scrollView: UIScrollView) {

let pan = scrollView.panGestureRecognizer

let velocity = pan.velocityInView(scrollView).y

if velocity < -5 {

self.navigationController?.setNavigationBarHidden(true, animated: true)

} else if velocity > 5 {

self.navigationController?.setNavigationBarHidden(false, animated: true)

}

}