Swift - 在后台将文件上传到S3

Question

在我的Swift应用程序中，我可以通过AWS SDK将图像上传到我的S3存储桶。现在，我必须等到文件成功上传后再解除视图。

let transferManager = AWSS3TransferManager.defaultS3TransferManager()
    let testFileURL1 = NSURL(fileURLWithPath: NSTemporaryDirectory().stringByAppendingPathComponent("temp"))
    let uploadRequest1 : AWSS3TransferManagerUploadRequest = AWSS3TransferManagerUploadRequest()

    let data = UIImageJPEGRepresentation(image, 0.5)
    data.writeToURL(testFileURL1!, atomically: true)
    uploadRequest1.bucket = "shrikar-picbucket"
    uploadRequest1.key =  "bingo"
    uploadRequest1.body = testFileURL1

    let task = transferManager.upload(uploadRequest1)
    task.continueWithBlock { (task) -> AnyObject! in
        if task.error != nil {
            println("Error: \(task.error)")
        } else {
            println("Upload successful")
            self.dismissViewControllerAnimated(true, completion: nil)
        }
        return nil
    }

即使我在上传完成之前关闭了视图，如何才能将其上传到后台？