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

问题描述

我需要使用初始化期间传递的 UIcollectionViewcell 在 URL 中加载 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，我需要使用这种方法以这种方式加载图像：

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)
            }
        }
    }
}

如图所示，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，加载图像需要一些时间，所以没有问题。

当我滚动浏览集合时出现问题，我看到某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，所以我这样做了（如果图像是通过 sd_setimage 和 getThumbnailImageFromVideoUrl 函数加载的） ):

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

但我在滚动时仍然发现图像不匹配，认为 collection view，可能是什么问题？

解决方法

我认为问题不在于图像，我猜是视频缩略图。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用以及您刚刚创建的图像是否已过时。

所以在你的单元格中

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)
                }
            }
        }