如何使用UIPageViewController在每个页面的底部添加一个按钮？

import UIKit

class CustomViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let button = UIButton(type: .system)
        button.setTitle("按钮", for: .normal)
        button.frame = CGRect(x: 0, y: view.frame.height - 50, width: view.frame.width, height: 50)
        view.addSubview(button)
    }
}

class PageViewController: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {
    lazy var pages: [UIViewController] = {
        return [
            CustomViewController(),
            CustomViewController(),
            CustomViewController()
        ]
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        dataSource = self
        delegate = self
        
        setViewControllers([pages[0]], direction: .forward, animated: true, completion: nil)
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let index = pages.firstIndex(of: viewController), index > 0 else {
            return nil
        }
        return pages[index - 1]
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let index = pages.firstIndex(of: viewController), index < pages.count - 1 else {
            return nil
        }
        return pages[index + 1]
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        guard completed, let currentViewController = viewControllers?.first else {
            return
        }
        
        // 更新按钮状态
        if let customViewController = currentViewController as? CustomViewController {
            // 更新按钮状态
        }
    }
}

// 在父视图控制器中使用PageViewController
class ParentViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let pageViewController = PageViewController(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
        addChild(pageViewController)
        view.addSubview(pageViewController.view)
        pageViewController.didMove(toParent: self)
    }
}