尝试滚动超出scrollView限制时检测拖动方向

import UIKit

class ViewController: UIViewController, UIScrollViewDelegate {
    var lastContentOffset: CGFloat = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let scrollView = UIScrollView(frame: CGRect(x: 0, y: 0, width: view.frame.width, height: view.frame.height))
        scrollView.contentSize = CGSize(width: view.frame.width, height: view.frame.height * 2)
        scrollView.delegate = self
        view.addSubview(scrollView)
    }
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if scrollView.contentOffset.y > lastContentOffset {
            // 向下拖动
            print("向下拖动")
        } else if scrollView.contentOffset.y < lastContentOffset {
            // 向上拖动
            print("向上拖动")
        }
        
        lastContentOffset = scrollView.contentOffset.y
    }
}