为什么我的 collectionview 单元格没有动画？

问题描述

我有集合视图单元格，我想同时为它们设置动画。即使我使用 UIView.animate，动画也不会发生，仿射变换会立即发生。

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
        cell.moveText = 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: 2,repeats: true) { timer in
            UIView.animate(withDuration: 1,delay: 0) {
                print("Starting animatings")
                self.moveText = !self.moveText
                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 = CGAffineTransform(translationX: 0,y: 0)
            }
        }
    }
    
    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")
    }
}

解决方法

这是因为你制作了错误的动画。

// adding weak self so the timer will not retain the view controller
Timer.scheduledTimer(withTimeInterval: 2,repeats: true) { [weak self] timer in
    self?.moveText.toggle() // you can use toggle() on a `Bool`
    self?.collectionview.reloadData()
}

相反，您应该尝试动画设置单个单元格的值

func collectionView(_ collectionView: UICollectionView,cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionview.dequeueReusableCell(withReuseIdentifier: "cell",for: indexPath) as! MyCell
    UIView.animate(withDuration: 1,delay: 0) {
        cell.moveText = self.moveText
    }
    return cell
}

此外，您可以使用 CGAffineTransform(translationX: 0,y: 0) 代替 .identity

label.transform = .identity

值得注意的是，每 2 秒重新加载集合视图并直接在 cellForItemAt 中进行动画是非常低效的。您应该找到另一种方法将信息传递给单元格，它们应该为内容设置动画