如何控制 UICollectionViewCell 调整动画大小？

Question

我有一个关于如何控制 UICollectionViewCell 的调整大小动画的问题。为了更清楚，我想知道如何设置动画的持续时间和曲线。我有一个简单的 UICollectionView 流布局和一个包含按钮的单元格。点击按钮会导致单元格的高度发生变化。

这是我的代码：

class ViewController: UICollectionViewController {
    var isExpanded = false
    var cv: UICollectionView {
        get {
            return collectionView!
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        if let layout = collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
            layout.estimatedItemSize = CGSize(width: collectionView!.frame.width, height: 400.0)
        }

        collectionView?.delegate = self
        collectionView?.dataSource = self
    }

    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 1
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! CollectionViewCell
        cell.parent = self
        return cell
    }
}

    extension ViewController: UICollectionViewDelegateFlowLayout {
        func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let cell = collectionView.cellForItem(at: indexPath) as? CollectionViewCell
        /*
         Need to calculate cell's height.
         */
        return isExpanded ? CGSize(width: collectionView.frame.width, height: 400) : CGSize(width: collectionView.frame.width, height: 200)
    }
}

这是我的单元格的代码

class CollectionViewCell: UICollectionViewCell {
    var heightConstraint: NSLayoutConstraint!
    var isExpanded = false
    var parent: ViewController! {
        didSet {
          contentView.widthAnchor.constraint(equalToConstant: parent.view.frame.width).isActive = true
          heightConstraint = NSLayoutConstraint(item: contentView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 200.0)
          contentView.addConstraint(heightConstraint)
        }
    }

    @IBOutlet weak var height: NSLayoutConstraint!

    override func awakeFromNib() {
        super.awakeFromNib()
        contentView.translatesAutoresizingMaskIntoConstraints = false
    }

    @IBAction func expand(_ sender: Any) {
        self.parent.cv.performBatchUpdates({
            //This UIView animate block doesn't matter anything actually.
            UIView.animate(withDuration: 10.5, animations: {[unowned self] in
            self.isExpanded = !self.isExpanded
            self.heightConstraint.constant = self.isExpanded ? 400.0 : 200.0
            self.layoutIfNeeded()
            }, completion: nil)
    }, completion: nil)
}

如您所见，我决定为这个示例制作相当长的动画，因此，我注意到 UIView.animate 块实际上不会影响单元格的调整大小动画。我想我应该寻找 CAAnimation 或类似的东西。很高兴听到任何想法！谢谢。

Answer 1

要实现这一点，您需要通过添加CABasicAnimation 类型的属性来扩展UICollectionViewLayoutAtteributes。

这在This answer中有很好的描述