Resume Data from URLSessionDownloadTask Always nil - swift3

Question

i have an app which i need to download the file from the internet when i downloading the file it's work good but my problem is when i pressed pause button to pause the downloading for one minute or more i get nil from resume Data
the following my code :
#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)
}
}
please can help me
thanks for all

Answer 1

Your code seems to be correct, you just need to init the downloadData with resumeData in closure
Make a property of downloadData
var downloadData:Data!
and then in your pause button action where you cancel the task, set the downloadData with 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
})
In order to check the progress and completion, implement these URLSessionDownloadDelegate delegates
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")
}
NOTE:- Try a valid downloadable url. For example
http://www.star.uclan.ac.uk/news_and_events/news/2010020901/sdo_resolution_comparison.png
Its http, make sure to set Transport Security in Info.plist