未调用NSURLSession委托 [英] NSURLSession delegates not called

问题描述

在下面的代码中，文件下载得很好。但是，似乎没有调用任何委托方法，因为我没有收到任何输出。 progressView也不会更新。知道为什么吗？

In the following code, the file downloads just fine. However none of the delegate methods seem to be called as I receive no output whatsoever. the progressView is not updated either. Any idea why?

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)

}
}

推荐答案

从我的测试中，你必须选择是否要使用委托或完成处理程序 - 如果你指定b oth，只调用完成处理程序。此代码为我提供了运行进度更新和 didFinishDownloadingToURL 事件：

From my testing, you have to choose whether you want to use a delegate or a completion handler - if you specify both, only the completion handler gets called. This code gave me running progress updates and the didFinishDownloadingToURL event:

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)
}

---

来自 NSURLSession 文档，这里是相关部分：

---

From the NSURLSession documentation, here's the relevant section:

与大多数网络API一样，NSURLSession API是高度异步的。它以两种方式之一返回数据，具体取决于您调用的方法：

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

• 到完成处理程序块时，将数据返回给您的应用程序传输成功完成或出现错误。


• 通过在收到数据时调用自定义代理上的方法。


• 通过调用自定义方法下载到文件完成时委托。

因此，按设计，它会将数据返回到 完成处理程序阻止或委托。但正如这里所表明的那样，并非两者都有。

So by design it returns data to either a completion handler block or a delegate. But as evinced here, not both.

这篇关于未调用NSURLSession委托的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！