iOS scrollview上拉显示Navbar下拉隐藏

动画效果：

显示隐藏.gif

关于下拉隐藏Nabbar,上拉显示，有三种方式：推崇第一种，但是做的还是没简书、知乎那样流畅,第一种是对navbar做了平移，第二种，第三种都是隐藏。。

第一种，和第二种处理时机一样，但是效果更好，并没有处理Navbar 的隐藏。

-(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{
    oldY = scrollView.contentOffset.y;
}
-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
        if (scrollView.contentOffset.y > oldY) {
  

            [UIView animateWithDuration:0.3 animations:^{
                self.navigationController.navigationBar.transform =
                CGAffineTransformMakeTranslation(0, -64);

            }];

           ;

        }else{
            [UIView animateWithDuration:0.3 animations:^{
                self.navigationController.navigationBar.transform =
                CGAffineTransformIdentity;

            }];
        }
}
-(void)viewWillDisappear:(BOOL)animated{
    self.navigationController.navigationBar.transform = CGAffineTransformIdentity;

}

第二种：在开始拖拽的时候保存偏移量，结束拖拽的时候比较当前偏移量，判断是否隐藏Navbar。

-(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{
    oldY = scrollView.contentOffset.y;
}
-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
        if (scrollView.contentOffset.y > oldY) {
  
            [CATransaction begin];
            [CATransaction setAnimationDuration:1.0];
            [CATransaction setAnimationTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear]];
            //set the position
            [self.navigationController setNavigationBarHidden:YES animated:YES];
            [CATransaction commit];
           ;

        }else{
            [CATransaction begin];
            [CATransaction setAnimationDuration:1.0];
            [CATransaction setAnimationTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear]];
             [self.navigationController setNavigationBarHidden:NO animated:YES];
             [CATransaction commit];

        }
}

第三种： 是根据拖拽的velocity进行判断，很霸道但是效果不如第一种,,隐藏的时机不对你可以做个比较；

这种方法引自文章：滑动隐藏

-(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];
        
    }
    
}

最后选择合适的时候恢复Navbar 的状态，建议放在viewWillDisappear里,否则在进入下一个页面里很突兀。

-(void)viewWillDisappear:(BOOL)animated{
    [self.navigationController setNavigationBarHidden:NO animated:YES];
}