滚动时 collectionView 单元格图像更改 - swift - 以编程方式

Question

我需要使用我在初始化期间传递的 URL 在 UIcollectionViewcell 中加载一个 ImageView：

func configureCellWith(messageModel : MessageModel){
    
    guard let url = URL(string: messageModel.contentUrl!) else { return }
    
    if url.isURLPhoto(){
        likedImageView.sd_setImage(with: url, placeholderImage: nil)
    }
    else if url.isURLVideo(){
        getThumbnailImageFromVideoUrl(url: url) { (image) in
            self.likedImageView.image = image
    }
}

如果url是视频我需要用这个方法加载图片：

func getThumbnailImageFromVideoUrl(url: URL, completion: @escaping ((_ image: UIImage?)->Void)) {
    DispatchQueue.global().async {
        let asset = AVAsset(url: url)
        let avAssetImageGenerator = AVAssetImageGenerator(asset: asset)
        avAssetImageGenerator.appliesPreferredTrackTransform = true
        let thumnailTime = CMTimeMake(value: 2, timescale: 1)
        do {
            let cgThumbImage = try avAssetImageGenerator.copyCGImage(at: thumnailTime, actualTime: nil)
            let thumbNailImage = UIImage(cgImage: cgThumbImage)
            DispatchQueue.main.async {
                completion(thumbNailImage)
            }
        } catch {
            print(error.localizedDescription)
            DispatchQueue.main.async {
                completion(nil)
            }
        }
    }
}

可见我检索了视频的初始帧并将其加载到单元格中，显然由于它是一个异步函数，因此加载图像需要一些时间，这没有问题。

当我滚动浏览集合时出现问题，我看到一些单元格显示的图像与正确的图像不对应。

在线搜索我发现我需要清除单元格 prepareForReuse 中的图像，所以我做了（这两种情况都是通过 sd_setImage 加载图像，虽然 getThumbnailImageFromVideoUrl 函数):

override func prepareForReuse() {
    super.prepareForReuse()
    self.likedImageView.image = UIImage()
    self.likedImageView.image = nil
    self.likedImageView.sd_cancelCurrentImageLoad()
    
}

但是当我想到 collection view 滚动时，我仍然得到不匹配的图像，可能是什么问题？

Answer 1

我认为问题不在于图片，我想是视频缩略图。您在后台线程上同步生成缩略图，但在将其设置回 imageView 时，您从不费心去查找单元格是否被重复使用以及您刚刚创建的图像是否已过时。

所以在你的牢房里

var  currentModel: MessageModel! = nil //declare a instance variable to hold model
... other code

func configureCellWith(messageModel : MessageModel){
    self.currentModel = messageModel //keep a copy of model passed to u as argument

    guard let url = URL(string: messageModel.contentUrl!) else { return }
    
    if url.isURLPhoto(){
        likedImageView.sd_setImage(with: url, placeholderImage: nil)
    }
    else if url.isURLVideo(){
        getThumbnailImageFromVideoUrl(url: url) { (image) in
            self.likedImageView.image = image
    }
}

终于在getThumbnailImageFromVideoUrl

func getThumbnailImageFromVideoUrl(url: URL, completion: @escaping ((_ image: UIImage?)->Void)) {
        DispatchQueue.global().async {
            let asset = AVAsset(url: url)
            let avAssetImageGenerator = AVAssetImageGenerator(asset: asset)
            avAssetImageGenerator.appliesPreferredTrackTransform = true
            let thumnailTime = CMTimeMake(value: 2, timescale: 1)
            do {
                let cgThumbImage = try avAssetImageGenerator.copyCGImage(at: thumnailTime, actualTime: nil)
                let thumbNailImage = UIImage(cgImage: cgThumbImage)
                if url.absoluteString == currentModel.contentUrl { //check if image you generated is still valid or its no longer needed
                    DispatchQueue.main.async {
                        completion(thumbNailImage)
                    }
                }
            } catch {
                print(error.localizedDescription)
                DispatchQueue.main.async {
                    completion(nil)
                }
            }
        }

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