当按下UINavigationController的back bar按钮时执行操作

class CustomNavigationController: UINavigationController {
    override var viewControllers: [UIViewController]? {
        didSet {
            if let previousViewController = oldValue?.last, let currentViewController = viewControllers?.last {
                // 在这里执行你需要的操作
                print("从\(previousViewController)返回到\(currentViewController)")
            }
        }
    }
}

class ViewController: UIViewController, UINavigationControllerDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        navigationController?.delegate = self
    }

    func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {
        if let previousViewController = navigationController.viewControllers.first(where: { $0 !== viewController }) {
            // 在这里执行你需要的操作
            print("从\(previousViewController)返回到\(viewController)")
        }
    }
}