iOS UICollectionView 显示帧动画

利用 UIImageView 的 animationImages 显示帧动画，每个 cell 上都显示，经过测试，会出现如下几个问题：

1. 滑动 collectionView 后部分 cell 上的 imageView 不再播放动画
2. 点按 cell 跳转到另一个界面，再返回，这个 cell 上的 imageView 不再播放动画

解决：
在自定义 UICollectionViewCell 中加代码：

    override func prepareForReuse() {
        super.prepareForReuse()
        endPlayImages()
    }
    
    var images: [UIImage]? // cell 缓存 images
    func playImages(_ images: [UIImage]? = nil) {
        if images != nil {
            self.images = images
        }
        
        guard let imgs = self.images else {
            return
        }
        previewIV.animationImages = imgs
        previewIV.animationDuration = TimeInterval(imgs.count * 1)
        previewIV.highlightedAnimationImages = imgs
        previewIV.startAnimating()
    }
    
    func endPlayImages() {
        previewIV.stopAnimating()
    }

然后到 UIViewController 中添加代码：

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        playAllImages() // 点到别的界面，返回，需要重新播放动画
    }
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        playAllImages() // 滑动后重新播放动画
    }

 extension ViewController: UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        playImage(collectionView: collectionView, indexPath: indexPath)
    }

    func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
        playImage(collectionView: collectionView, indexPath: indexPath)
    }

    func collectionView(_ collectionView: UICollectionView, didHighlightItemAt indexPath: IndexPath) {
        playImage(collectionView: collectionView, indexPath: indexPath)

    }

    func collectionView(_ collectionView: UICollectionView, didUnhighlightItemAt indexPath: IndexPath) {
        playImage(collectionView: collectionView, indexPath: indexPath)
    }

}


extension ViewController {
    func playAllImages() {
        let visibleCellIndex = self.galleryTypesView.locolCollection.indexPathsForVisibleItems
        
        for (i,cell) in self.galleryTypesView.locolCollection.visibleCells.enumerated()  {
            let indexPath = visibleCellIndex[i]
            if localWorks[indexPath.row].type == .animation {
                let cardCell = cell as! CardCollectionCell
                cardCell.playImages()
            }
        }
    }
    
    func playImage(collectionView: UICollectionView, indexPath: IndexPath) {
        let cardCell = collectionView.dequeueReusableCell(withReuseIdentifier: CardCollectionCell.description(), for: indexPath) as! CardCollectionCell
        cardCell.playImages()
    }
}