NSURLSession delegati non chiamati

Question

Nel seguente codice, il file viene scaricato correttamente. Tuttavia nessuno dei metodi delegati sembra essere chiamato in quanto non ricevo output di sorta. neanche il progressView non è aggiornato. Qualche idea del perché?

import Foundation 
import UIKit 

class Podcast: PFQueryTableViewController, UINavigationControllerDelegate, MWFeedParserDelegate, UITableViewDataSource, NSURLSessionDelegate, NSURLSessionDownloadDelegate { 

    func downloadEpisodeWithFeedItem(episodeURL: NSURL) { 

    var request: NSURLRequest = NSURLRequest(URL: episodeURL) 
    let config = NSURLSessionConfiguration.defaultSessionConfiguration() 
    let session = NSURLSession(configuration: config, delegate: self, delegateQueue: nil) 

    var downloadTask = session.downloadTaskWithURL(episodeURL, completionHandler: { (url, response, error) -> Void in 
     println("task completed") 
     if (error != nil) { 
      println(error.localizedDescription) 
     } else { 
      println("no error") 
      println(response) 
     } 
    }) 
    downloadTask.resume() 

} 

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didResumeAtOffset fileOffset: Int64, expectedTotalBytes: Int64) { 
    println("didResumeAtOffset") 
} 

    func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) { 
      var downloadProgress = Double(totalBytesWritten)/Double(totalBytesExpectedToWrite) 
    println(Float(downloadProgress)) 
    println("sup") 

    epCell.progressView.progress = Float(downloadProgress) 
} 

    func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didFinishDownloadingToURL location: NSURL) { 
    println(location) 

} 
} 

Answer 1

Dal mio test, è necessario scegliere se si desidera utilizzare un delegato o di un gestore di completamento - se si specifica entrambi, solo il gestore di completamento viene chiamato. Questo codice mi ha dato esecuzione aggiornamenti sullo stato di avanzamento e l'evento didFinishDownloadingToURL:

func downloadEpisodeWithFeedItem(episodeURL: NSURL) { 
    let request: NSURLRequest = NSURLRequest(URL: episodeURL) 
    let config = NSURLSessionConfiguration.defaultSessionConfiguration() 
    let session = NSURLSession(configuration: config, delegate: self, delegateQueue: NSOperationQueue.mainQueue()) 

    let downloadTask = session.downloadTaskWithURL(episodeURL) 
    downloadTask.resume() 
} 

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didResumeAtOffset fileOffset: Int64, expectedTotalBytes: Int64) { 
    println("didResumeAtOffset: \(fileOffset)") 
} 

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) { 
    var downloadProgress = Double(totalBytesWritten)/Double(totalBytesExpectedToWrite) 
    println("downloadProgress: \(downloadProgress)") 
} 

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didFinishDownloadingToURL location: NSURL) { 
    println("didFinishDownloadingToURL: \(location)") 
    println(downloadTask) 
} 

---

Dal NSURLSession documentation, ecco la sezione pertinente:

Like most networking APIs, the NSURLSession API is highly asynchronous. It returns data in one of two ways, depending on the methods you call:

• To a completion handler block that returns data to your app when a transfer finishes successfully or with an error.
• By calling methods on your custom delegate as the data is received.
• By calling methods on your custom delegate when download to a file is complete.

Così da un design che restituisce i dati a sia un completamento handler block o un delegato. Ma come è stato dimostrato qui, non entrambi.

Answer 2

interessante, Apple specifically explains this behavior in their NSURLSessionDataDelegate (ma né nel delegato di base NSURLSessionTaskDelegate né NSURLSessionDownloadDelegate)

NOTE

An NSURLSession object need not have a delegate. If no delegate is assigned, when you create tasks in that session, you must provide a completion handler block to obtain the data.

Completion handler block are primarily intended as an alternative to using a custom delegate. If you create a task using a method that takes a completion handler block, the delegate methods for response and data delivery are not called.

Answer 3

Swift 3

class ViewController: UIViewController { 
    var urlLink: URL! 
    var defaultSession: URLSession! 
    var downloadTask: URLSessionDownloadTask! 
} 

// MARK: Button Pressed 
    @IBAction func btnDownloadPressed(_ sender: UIButton) { 
     let urlLink1 = URL.init(string: "https://github.com/VivekVithlani/QRCodeReader/archive/master.zip") 
     startDownloading(url: urlLink!) 
} 
    @IBAction func btnResumePressed(_ sender: UIButton) { 
    downloadTask.resume() 
} 

@IBAction func btnStopPressed(_ sender: UIButton) { 
    downloadTask.cancel() 
} 

@IBAction func btnPausePressed(_ sender: UIButton) { 
    downloadTask.suspend() 
} 

    func startDownloading (url:URL) { 
     let backgroundSessionConfiguration = URLSessionConfiguration.background(withIdentifier: "backgroundSession") 
     defaultSession = Foundation.URLSession(configuration: backgroundSessionConfiguration, delegate: self, delegateQueue: OperationQueue.main) 
     downloadProgress.setProgress(0.0, animated: false) 
     downloadTask = defaultSession.downloadTask(with: urlLink) 
     downloadTask.resume() 
    } 

// MARK:- URLSessionDownloadDelegate 
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) { 
    print("File download succesfully") 
} 

func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) { 
    downloadProgress.setProgress(Float(totalBytesWritten)/Float(totalBytesExpectedToWrite), animated: true) 
} 

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) { 
    downloadTask = nil 
    downloadProgress.setProgress(0.0, animated: true) 
    if (error != nil) { 
     print("didCompleteWithError \(error?.localizedDescription)") 
    } 
    else { 
     print("The task finished successfully") 
    } 
}