A background URLSession with identifier com.example.DownloadTaskExample.background already exists!

var backgroundSession: URLSession!
var index = 0

override func viewDidLoad() {
    super.viewDidLoad()
    let sessionConfig = URLSessionConfiguration.background(withIdentifier: "com.example.Example.background")
        backgroundSession = URLSession(configuration: sessionConfig, delegate: self, delegateQueue: OperationQueue())
}

let url = URL(string: "link")!
let downloadTask1 = ViewController.backgroundSession.downloadTask(with: url)
downloadTask1()