让 setTitle 函数与 nextButton 一起工作时出现问题

Question

运行代码后，一切正常，除了

setTitle

命令会更改按钮内的文本。我已经尝试了一切，甚至复制了教程，但没有运气。我 2 天前开始使用 Swift，所以任何帮助都会很棒！

CVAimport UIKit

class OnboardingViewController: UIViewController {
    
    @IBOutlet weak var collectionView: UICollectionView!
    @IBOutlet weak var nextButton: UIButton!
    @IBOutlet weak var pageControl: UIPageControl!
    
    var slides: [OnboardingSlide] = []
    
    var currentPage = 0 {
        didSet {
            if currentPage == slides.count - 1 {
                nextButton.setTitle("GET STARTED", for: .normal)
            } else {
                nextButton.setTitle("NEXT", for: .normal)
            }
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        slides = [
            OnboardingSlide(title: "", description: "", image: #imageLiteral(resourceName: "")),
            OnboardingSlide(title: "", description: "", image: #imageLiteral(resourceName: "")),
            OnboardingSlide(title: "", description: "", image: #imageLiteral(resourceName: "")),
        ]
        pageControl.numberOfPages = slides.count
    }
    
    @IBAction func nextButtonClicked(_ sender: UIButton)
        {
            currentPage += 1
            let indexPath = IndexPath(item: currentPage, section: 0)
             collectionView.scrollToItem(at: indexPath, at: .centeredHorizontally, animated: true)
    }
    
}

extension OnboardingViewController: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return slides.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: OnboardingCollectionViewCell.identifier, for: indexPath) as! OnboardingCollectionViewCell
        cell.setup(slides[indexPath.row])
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: collectionView.frame.width, height: collectionView.frame.height)
    }
    
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        let width = scrollView.frame.width
        let currentPage = Int(scrollView.contentOffset.x / width)
        pageControl.currentPage = currentPage
    }
}

我几乎尝试了所有我能想到的方法，但我是 Swift 的新手，无法弄清楚为什么标题更改对我的标签和文本有效，但对按钮中的文本无效。