处理多个文件（图像）上传到 AWS S3 Swift

我一直在尝试研究从 iOS 应用程序上传多个图像到 AWS S3 的最佳方法。我在 StackOverflow 上看到过一些类似的问题，其中最接近“答案”的问题就在这里：link https://stackoverflow.com/questions/41705839/efficient-way-to-upload-multiple-images-to-s3-from-ios。虽然我不完全理解线程/调度组/等，但我尝试了很多方法来实现上传多个图像的方法。我的设想是这样的：

1. 调用方法上传多张图片并传入多张图片
2. 迭代图像，通过调用特殊方法创建新的AWS S3上传请求（调用前输入调度组）
3. 在上传方法中使用完成处理程序根据是否发生成功/错误返回 true/false（在完成处理程序中，离开调度组）
4. 等待调度组任务完成，然后使用通知处理后续步骤

我沿着这些思路创造了类似的东西；然而，它似乎并没有 100% 发挥作用。我已经实现了一个 while 循环来检查“retryCount”，在警告用户上传请求不成功之前尝试 x 次。下面是我目前拥有的代码 - 请告诉我这是否正确处理流程/正确处理大量请求/等等。非常感谢！

static func uploadImages(imagesToUpload: [UIImage], complete: @escaping (String?) -> ()) {
    let folderKey = UUID().uuidString
    var retryArray = [String: Data]()
    var retryCount = 0

    for i in 0..<imagesToUpload.count {
        retryArray.updateValue(UIImagePNGRepresentation(imagesToUpload[i])!, forKey: "image\(i)")
        //retryArray["image\(i)"] = UIImagePNGRepresentation(imagesToUpload[i])
    }

    let imageGroup = DispatchGroup()
    imageGroup.enter()

    if(retryArray.keys.count > 0) {
        while(retryCount < 3) {
            //Iterate through retry array
            let uploadGroup = DispatchGroup()

            for (key, val) in retryArray {
                print("Trying to upload: \(key)")

                uploadGroup.enter()
                singleUpload(imageToUpload: val, keyVal: "public/\(folderKey)/\(key).png", complete: { (err) -> Void in
                    //If no error, remove key/value pair
                    if(!err) {
                        print("\(key) was successfully uploaded")
                        retryArray.removeValue(forKey: key)
                    }
                    uploadGroup.leave()
                })

            }
            uploadGroup.wait()
            if(retryArray.keys.count == 0) {
                break
            } else {
                retryCount = retryCount + 1
            }

        }
        imageGroup.leave()
    } else {
        imageGroup.leave()
    }

    imageGroup.notify(queue: DispatchQueue.main) {

        if(retryArray.keys.count > 0) {
            print("the images could not be uploaded")
            complete(nil)
            //execute code to delete folder in aws s3
        } else {
            print("all images uploaded successfully")
            complete(folderKey)
        }
    }
}

static func singleUpload(imageToUpload: Data, keyVal: String, complete: @escaping (Bool) -> ()) {

    var data: Data = Data() // Data to be uploaded
    data = imageToUpload

    let expression = AWSS3TransferUtilityUploadExpression()
    var completionHandler: AWSS3TransferUtilityUploadCompletionHandlerBlock?
    completionHandler = { (task, error) -> Void in
        //DispatchQueue.main.async(execute: {
            if let error = error {
                complete(true)
            }
            else{
                complete(false)
            }
        //})
    }

    let transferUtility = AWSS3TransferUtility.default()

    transferUtility.uploadData(data,
                               bucket: s3BucketName,
                               key: keyVal,
                               contentType: "image/png",
                               expression: expression,
                               completionHandler: completionHandler).continueWith {
                                (task) -> AnyObject! in
                                if let error = task.error {
                                    print("Error: \(error.localizedDescription)")
                                    complete(true)
                                }

                                if let _ = task.result {
                                    // Do something with uploadTask.
                                }
                                return nil;
    }
}

另外 - 我很好奇是否有更好的方法来解决这个问题。不是创建要上传的项目列表，而是迭代（基于 retryCount x 次），尝试上传项目（并删除成功的项目），然后向用户呈现结果（如果 1，则全有或全无）图片未上传）。有没有更好的用户体验/效率途径？谢谢你！