func scrollViewDidScroll(_ scrollView: UIScrollView) {
        
        if(scrollView.contentOffset.y > 0)
        {
            if(scrollView.contentOffset.y < imageViewHeight - (view.bounds.height / 3))
            {
                //이미지 뷰의 높이보다 작게 스크롤 되면 이미지뷰의 높이를 줄이고, 줄이는 만큼 Y 를 띄워준다.
                imageViewTopConstraint.constant = scrollView.contentOffset.y
                imageViewHeightConstraint.constant = imageViewHeight - scrollView.contentOffset.y
                self.navigationController?.setNavigationBarHidden(true, animated: true);
                
                if(self.topViewTopConstraint.constant != 0)
                {
                    self.topViewTopConstraint.constant = 0
                    
                    UIView.animate(withDuration: 1.0) {
                        self.view.layoutIfNeeded()
                    }
                }
            }
            else
            {
                //이미지 뷰의 높이보다 많이 스크롤 되면 네비게이션을 보여준다.
                imageViewTopConstraint.constant = imageViewHeight - (view.bounds.height / 3)
                imageViewHeightConstraint.constant = (view.bounds.height / 3)
                self.navigationController?.setNavigationBarHidden(false, animated: true);
                
                if(self.topViewTopConstraint.constant != -self.topView.bounds.height)
                {
                    self.topViewTopConstraint.constant = -self.topView.bounds.height
                    
                    UIView.animate(withDuration: 1.0) {
                        self.view.layoutIfNeeded()
                    }
                }
            }
        }
        else
        {
            //기본값을 설정한다.
            imageViewTopConstraint.constant = 0
            imageViewHeightConstraint.constant = imageViewHeight
            self.navigationController?.setNavigationBarHidden(true, animated: true);
            
            if(self.topViewTopConstraint.constant != 0)
            {
                self.topViewTopConstraint.constant = 0
                
                UIView.animate(withDuration: 1.0) {
                    self.view.layoutIfNeeded()
                }
            }
        }
    }