如何从 UICollectionViewController 中的 scrollViewDidScroll 方法访问单元格成员（用于动画）？

Posted 2023-02-24

【中文标题】如何从 UICollectionViewController 中的 scrollViewDidScroll 方法访问单元格成员（用于动画）？

【英文标题】：How to access cell members (for animation) from scrollViewDidScroll method in UICollectionViewController?

【发布时间】：2019-10-08 09:46:53

【问题描述】：

如何通过 UICollectionViewController 中的 scrollViewDidScroll 方法访问添加到 UICollectionViewCell 中的视图的成员（UIImage 或 UITextView）？

我想制作动画，即在垂直滚动到下一个单元格时以“不同的速度”移动图像和文本。

我知道这可以在 scrollViewDidScroll 方法中完成，但我不知道如何访问成员。

视图控制器：

class OnboardingViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout 

    override func scrollViewDidScroll(_ scrollView: UIScrollView) 
     **code here which I just can't figure out....**
    

    override func viewDidLoad() 
        super.viewDidLoad()

        collectionView?.backgroundColor = .white
        collectionView?.register(PageCell.self, forCellWithReuseIdentifier: "cellId")
        collectionView?.isPagingEnabled = true
        collectionView.showsHorizontalScrollIndicator = false

        // this method "creates" the UIPageControll and assigns  
        setupPageControl()
    

    lazy var pageControl: UIPageControl = 
        let pageControl = UIPageControl()
        pageControl.currentPage     = 0
        pageControl.numberOfPages   = data.count <--- data provided by a model from a plist - works perfectly
        pageControl.currentPageIndicatorTintColor   = .black
        pageControl.pageIndicatorTintColor          = .gray
        pageControl.translatesAutoresizingMaskIntoConstraints  = false

        return pageControl
    ()

    private func setupPageControl() 
        view.addSubview(pageControl)
        NSLayoutConstraint.activate([
            onboardingPageControl.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
            onboardingPageControl.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 16),
            onboardingPageControl.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -16),
        ])
    

所有其他覆盖方法都在扩展中实现并且工作正常，即

numberOfItemsInSection section: Int) -> Int 
        return data.count
    

这是 PageCell：

class PageCell: UICollectionViewCell 

    var myPage: MyModel? 
        didSet 
            guard let unwrappedPage = myPage else  return 

            // the image in question:
            myImage.image = UIImage(named: unwrappedPage.imageName)
            myImage.translatesAutoresizingMaskIntoConstraints = false
            myImage.contentMode   = .scaleAspectFit

            // the text in question
            let attributedText = NSMutableAttributedString(string: unwrappedPage.title, attributes: [:])
            attributedText.append(NSAttributedString(string: "\n\(unwrappedPage.description)", attributes: [:]))
            myText.attributedText = attributedText
            myText.translatesAutoresizingMaskIntoConstraints    = false
            myText.textColor                                    = .black
            myText.textAlignment                                = .center
            myText.isEditable                                   = false
            myText.isScrollEnabled                              = false
            myText.isSelectable                                 = false
    

    let myImage: UIImageView = 
        let imageView           = UIImageView()
        return imageView
    ()

    let myText: UITextView = 
        let textView    = UITextView()
        return textView
    ()

    fileprivate func setup() 
        addSubview(myImage)
        NSLayoutConstraint.activate([
            myImage.safeAreaLayoutGuide.topAnchor.constraint(equalTo: safeAreaLayoutGuide.topAnchor, constant: 60),
            myImage.centerXAnchor.constraint(equalTo: centerXAnchor),
            myImage.leadingAnchor.constraint(equalTo: leadingAnchor),
            myImage.trailingAnchor.constraint(equalTo: trailingAnchor),
            myImage.heightAnchor.constraint(equalTo: heightAnchor, multiplier: 0.4)
        ])

        addSubview(myText)
        NSLayoutConstraint.activate([
            myText.topAnchor.constraint(equalTo: myImage.bottomAnchor, constant: 16),
            myText.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 16),
            myText.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -16)
        ])
    

    override init(frame: CGRect) 
        super.init(frame: frame)
        setup()
    

    required init?(coder: NSCoder) 
        fatalError("init(coder:) has not been implemented")
    

【问题讨论】：

你要找的可能是视差效果，试着搜索一下

【参考方案1】：

您可以通过获取 collectionView 的当前可见单元格来实现这一点，如果您在 scrollViewDidEndDecelerating 中访问它们会很棒，而不是scrollViewDidScroll。

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) 
        for cell in collectionView.visibleCells 
          //cell.imageView 
          //cell.txtView
         // you can access both imageView and txtView here

        let indexPath = collectionView.indexPath(for: cell)
        print(indexPath) // this will give you indexPath as well to differentiate