iOS开发上下滑动UIScrollview隐藏或者显示导航栏的实例

self.navigationController.hidesBarsOnSwipe = YES; 

self.navigationController?.hidesBarsOnSwipe = true 

- (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
 }
}

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) 
  } 
   
 } 

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset</span> 

{ 
 if (velocity.y > 0.0) { 
  [self.navigationController setNavigationBarHidden:YES animated:YES]; 
 } else if (velocity.y < 0.0){ 
  [self.navigationController setNavigationBarHidden:NO animated:YES]; 
 } 
} 

func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) { 
  if velocity.y > 0 { 
   self.navigationController?.setNavigationBarHidden(true, animated: true) 
  } else if velocity.y < 0 { 
   self.navigationController?.setNavigationBarHidden(false, animated: true) 
  } 
 }