Alamofire 多张图片下载并保存在本地

Posted 2023-02-24

【中文标题】Alamofire 多张图片下载并保存在本地

【英文标题】：Almofire multiple images Download and save them locally

【发布时间】：2020-09-28 18:32:51

【问题描述】：

我有超过 500 个图像链接，我想在应用启动时下载这些图像并本地存储在应用文档目录中。我正在使用 Almofire 进行下载，但出现类似错误 “URLSession 任务被取消”和请求超时

func downloadAllImages(images:[String: String], retryCount: Int = 0,completion: @escaping((Bool)->Void))
        var success: Bool = true
        var failedImages = [String: String]()
        for (localName, severPath) in images 
            self.dispatchGroup.enter()
            
            let destination: DownloadRequest.Destination =  _, _ in
                let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
                let fileURL = documentsURL.appendingPathComponent(localName)
                return (fileURL, [.removePreviousFile, .createIntermediateDirectories])
            
           
            
            let path = severPath.replacingOccurrences(of: "\\", with: "/").addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed) ?? ""
        
            //AF.sessionConfiguration.httpShouldSetCookies = false
            AF.download(path, to: destination).response  response in
                switch response.result 
                case .success(_):
                    break
                case .failure(let error):
                    if response.response?.statusCode != 404 
                        success = false
                        failedImages[localName] = path
                        print("Image Download Error = \(error.localizedDescription)")
                    
                    break
                
                debugPrint(response)
                self.dispatchGroup.leave()
            
        
        dispatchGroup.notify(queue: .main) 
            //retry If some Images failed to download
            if failedImages.isEmpty || retryCount >= self.maximumRetryCount 
                completion(success)
            else 
                self.downloadAllImages(images: failedImages, retryCount: retryCount + 1)  (success) in
                    completion(success)
                
            
        
    

图像字典包含 localName 作为键 serverPath 作为值

【参考方案1】：

AFImageDownloaders 有活动下载限制，我相信更改 maximumActiveDownloads 或 API 中的类似内容可以解决这个问题。新的下载只是取消了以前的下载。但最好分块下载。

例如这个是 ImageDownloader

 public init(session: Session,
                downloadPrioritization: DownloadPrioritization = .fifo,
                maximumActiveDownloads: Int = 4,
                imageCache: ImageRequestCache? = AutoPurgingImageCache()) 
        precondition(!session.startRequestsImmediately, "Session must set `startRequestsImmediately` to `false`.")

        self.session = session
        self.downloadPrioritization = downloadPrioritization
        self.maximumActiveDownloads = maximumActiveDownloads
        self.imageCache = imageCache
    

更新： 限制不在 AF 上，而是在 URLSession 上。一个 AF 下载器使用一个 URLSession。你必须通过自定义URLSessionConfigurations 来处理更多的活跃下载HTTPMaximumConnectionsPerHost。并将其传递给 AF Session 类