从 URLSessionDownloadTask 恢复数据 始终为零

Question

我有一个应用程序，当我下载文件时，我需要从互联网下载文件，但我的问题是当我按下暂停按钮以暂停下载一分钟或更长时间时，我从恢复数据中得到零

下面是我的代码：

@IBAction func startDownloading(_ sender: UIButton)
{     
    isDownload = true
    sessionConfig = URLSessionConfiguration.default
    let operationQueue = OperationQueue.main
    session = URLSession.init(configuration: sessionConfig, delegate: self, delegateQueue: operationQueue)
    let url = URL(string: "www.example.com")
    downloadTask = session.downloadTask(with: url!)
    downloadTask.resume()
}
@IBAction func pause(_ sender: UIButton) 
{
    if downloadTask != nil && isDownload 
    {
        self.downloadTask!.cancel(byProducingResumeData: { (resumeData) in
                        // here is the nil from the resume data
                    })
        isDownload = false
        downloadTask = nil
        pasueBtnOutlet.setTitle("Resume", for: .normal)
    }
    if !isDownload && downloadData != nil 
    {
        downloadTask = session.downloadTask(withResumeData: downloadData as Data)
        downloadTask.resume()
        isDownload = true
        downloadData = nil
        pasueBtnOutlet.setTitle("Pause", for: .normal)
    }                    
}

请帮帮我

谢谢大家

Answer 1

您的代码似乎是正确的，您只需要在关闭时使用resumeData 来初始化downloadData

创建downloadData的属性

var downloadData:Data!

然后在取消任务的暂停按钮操作中，将downloadData 设置为resumeData

self.downloadTask!.cancel(byProducingResumeData: { (resumeData) in
        // here is the nil from the resume data

        // You have to set download data with resume data
        self.downloadData = resumeData
})

为了检查进度和完成情况，请实现这些URLSessionDownloadDelegate 代表

func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
    let progress = Float(totalBytesWritten) / Float(totalBytesExpectedToWrite)
    print(Int(progress * 100))

}

func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
    print("Downloading done")
}

注意：- 尝试一个有效的可下载网址。例如 http://www.star.uclan.ac.uk/news_and_events/news/2010020901/sdo_resolution_comparison.png

它的http，一定要在Info.plist中设置Transport Security