我正在构建一个用于从url下载视频的应用程序，但是我的问题是，当我第一次启动我的应用程序时，它运行得很好，但是当我尝试启动另一个视图控制器并返回时，它不再下载了，这是我的代码：-
var downloadTask: URLSessionDownloadTask!
var backgroundSession: URLSession!
override func viewDidLoad() {
super.viewDidLoad()
self.basheOneProgress.setProgress(0, animated: false)
sessionConfiguration()
}
// Session Configuration.....
func sessionConfiguration() {
let backgroundSessionConfiguration = URLSessionConfiguration.background(withIdentifier: "backgroundSession")
backgroundSession = Foundation.URLSession(configuration: backgroundSessionConfiguration, delegate: self, delegateQueue: OperationQueue.main)
}
// Download Bashe ONE Video.
@IBAction func downloadBasheOne(_ sender: Any) {
let basheOneURL = URL(string: "http://pertuk.com/bashe1.mp4")
downloadTask = backgroundSession.downloadTask(with: basheOneURL!)
if downloadTask != nil {
let alertController = UIAlertController(title: "Download", message: "Do you wanna download?", preferredStyle: .alert)
let yesButton = UIAlertAction(title: "Yes", style: .default) { (alertController: UIAlertAction) in
self.downloadTask.resume()
}
let cancelButton = UIAlertAction(title: "No", style: .cancel, handler: nil)
alertController.addAction(yesButton)
alertController.addAction(cancelButton)
self.present(alertController, animated: true, completion: nil)
} else {
let alertController = UIAlertController(title: "Download", message: "Resuming Download", preferredStyle: .alert)
let yesButton = UIAlertAction(title: "Yes", style: .default) { (alertAction: UIAlertAction) in
self.downloadTask.resume()
}
alertController.addAction(yesButton)
self.present(alertController, animated: true, completion: nil)
}
}
@IBAction func cancelBasheOne(_ sender: UIButton) {
if downloadTask == nil {
let alertController = UIAlertController(title: "0%", message: "", preferredStyle: .alert)
let action = UIAlertAction(title: "OK", style: .default, handler: nil)
alertController.addAction(action)
self.present(alertController, animated: true, completion: nil)
} else {
let alertController = UIAlertController(title: "Cancel", message: "Cancel This Download", preferredStyle: .alert)
let yesButton = UIAlertAction(title: "Yes", style: .default) { (action: UIAlertAction) in
self.downloadTask.cancel()
}
alertController.addAction(yesButton)
self.present(alertController, animated: true, completion: nil)
}
}
@IBOutlet var basheOneProgress: UIProgressView!
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
let url = downloadTask.response?.url?.lastPathComponent
if (url?.hasSuffix(".mp4"))! {
guard let documentsDirectoryURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return }
if !FileManager.default.fileExists(atPath: documentsDirectoryURL.appendingPathComponent((downloadTask.response?.url?.lastPathComponent)!).path) {
let destinationURL = documentsDirectoryURL.appendingPathComponent(downloadTask.response?.suggestedFilename ?? ((downloadTask.response?.url)?.lastPathComponent)!)
do {
try? FileManager.default.removeItem(at: destinationURL)
try FileManager.default.moveItem(at: location, to: destinationURL)
PHPhotoLibrary.requestAuthorization({(authorizationStatus: PHAuthorizationStatus) -> Void in
// check if user authorized access photos for your app
if authorizationStatus == .authorized {
PHPhotoLibrary.shared().performChanges({
PHAssetChangeRequest.creationRequestForAssetFromVideo(atFileURL: destinationURL)
})
{ completed, error in
if completed {
DispatchQueue.main.async {
print("Video saved") // successfully saved video in your gallery
}
} else {
print(error as Any)
}
}
}
})
} catch {print(error)}
} else {
let destinationURL = documentsDirectoryURL.appendingPathComponent(downloadTask.response?.suggestedFilename ?? ((downloadTask.response?.url)?.lastPathComponent)!)
do {
try FileManager.default.removeItem(at: destinationURL)
try FileManager.default.moveItem(at: location, to: destinationURL)
PHPhotoLibrary.requestAuthorization({(authorizationStatus: PHAuthorizationStatus) -> Void in
// check if user authorized access photos for your app
if authorizationStatus == .authorized {
PHPhotoLibrary.shared().performChanges({
PHAssetChangeRequest.creationRequestForAssetFromVideo(atFileURL: destinationURL)
})
{ completed, error in
if completed {
DispatchQueue.main.async {
print("Video saved") // successfully saved video in your gallery
}
} else {
print(error as Any)
}
}
}
})
} catch {print(error)}
}
} else {
}
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
if totalBytesExpectedToWrite > 0 {
basheOneProgress.setProgress(Float(totalBytesWritten)/Float(totalBytesExpectedToWrite), animated: true)
} else if totalBytesExpectedToWrite == 0 {
basheOneProgress.setProgress(0.0, animated: false)
} else if totalBytesWritten == 100 {
basheOneProgress.setProgress(100, animated: false)
}
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
downloadTask = nil
basheOneProgress.setProgress(0, animated: false)
if (error != nil) {
print(error!.localizedDescription)
} else {
print("The Data Finished Transfering")
}
}
}
这是我回到下载视频的ViewController时的错误代码：-
（标识符为backgroundSession的后台URLSession已经存在！）