尝试在collectionview中为不可见单元格设置动画时如何防止延迟

Question

我想为我的所有 collectionview 单元格设置动画，这个简化的示例说明了这个问题。问题是，如果我在动画单元格时向下滚动，那么不可见的单元格会延迟动画。我希望不可见的单元格处于动画的最终状态，而不是动画延迟。

在视频中你看到，当我滚动到底部时，最后的单元格开始延迟动画。

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    
    var collectionview: UICollectionView!
    var moveText: Bool = false

    override func viewDidLoad() {
        super.viewDidLoad()
        
        collectionview = UICollectionView(frame: .zero, collectionViewLayout: UICollectionViewFlowLayout())
        collectionview.translatesAutoresizingMaskIntoConstraints = false
        collectionview.dataSource = self
        collectionview.delegate = self
        collectionview.backgroundColor = .systemBackground
        collectionview.register(MyCell.self, forCellWithReuseIdentifier: "cell")
        view.addSubview(collectionview)
        
        NSLayoutConstraint.activate([
            collectionview.topAnchor.constraint(equalTo: view.topAnchor),
            collectionview.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            collectionview.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            collectionview.trailingAnchor.constraint(equalTo: view.trailingAnchor)
        ])
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        10
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionview.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! MyCell
        UIView.animate(withDuration: 1, delay: 0, options: [
            UIView.AnimationOptions.allowAnimatedContent,
            UIView.AnimationOptions.allowUserInteraction,
        ]) {
            cell.moveText = self.moveText
        }
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return .init(width: collectionview.frame.width, height: 120)
    }
    
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        Timer.scheduledTimer(withTimeInterval: 1.5, repeats: true) { timer in
            print("Starting animatings")
            self.moveText.toggle()
            self.collectionview.reloadData()

        }
    }
    
}

class MyCell: UICollectionViewCell {
    
    let label = UILabel()
    var moveText: Bool = false {
        didSet {
            if moveText == true {
                label.transform = CGAffineTransform(translationX: 50, y: 50)
            } else {
                label.transform = .identity
            }
        }
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        label.text = "mytext"
        label.translatesAutoresizingMaskIntoConstraints = false
        addSubview(label)
        NSLayoutConstraint.activate([
            label.leadingAnchor.constraint(equalTo: leadingAnchor),
            label.topAnchor.constraint(equalTo: topAnchor)
        ])
        backgroundColor = .orange
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Answer 1

而不是在cellForItemAt 中添加这个辅助函数。

private func animateVisibleCells() {
    collectionview.visibleCells.compactMap { $0 as? MyCell }.forEach { cell in
        UIView.animate(withDuration: 1, delay: 0, options: [
            UIView.AnimationOptions.allowAnimatedContent,
            UIView.AnimationOptions.allowUserInteraction,
        ]) {
            cell.moveText = self.moveText
        }
    }
}

现在调用它而不是重新加载集合视图

Timer.scheduledTimer(withTimeInterval: 1.5, repeats: true) { timer in
    print("Starting animatings")
    self.moveText.toggle()
    self.animateVisibleCells()
}

并将cellForItemAt 实现转换为：

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionview.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! MyCell
    cell.moveText = moveText
    return cell
}