Question

我的应用程序同时下载多个文件。我的方案如下：

用户点击下载按钮。
初始化下载UITableViewCell，实现NSURLSessionDelegate以下载指定文件。
开始下载。下载单元格显示在使用NSURLSession提供的代理下载文件时的进度。
文件本地保存在文档文件夹中。
用户单击按钮可清除所有已完成的下载。此按钮清除阵列＆＃39; downloadQueue＆＃39; Download Cell使用。该按钮还调用tableView.reloadData来更新tableView

问题是，当用户启动多次下载时，不会出现问题。所有文件同时正确下载。但是，当用户单击步骤5中描述的按钮，然后尝试下载另一个文件时，下载进度会立即显示100％完成。并且没有文件在本地保存。这可能是因为立刻调用了didFinishDownloadingToURL。

以下是我的DownloadCell.swift的完整代码

class DownloadCell: UITableViewCell, NSURLSessionDelegate {


@IBOutlet weak var lblSongName: UILabel!
@IBOutlet weak var progressBar: UIProgressView!
@IBOutlet weak var progressCount: UILabel!

var song: Song!

var task: NSURLSessionTask!

var percentageWritten: Float = 0.0
var taskTotalBytesWritten = 0
var taskTotalBytesExpectedToWrite = 0

lazy var session: NSURLSession = {
    let config = NSURLSessionConfiguration.ephemeralSessionConfiguration()
    config.allowsCellularAccess = false
    let session = NSURLSession(configuration: config, delegate: self, delegateQueue: NSOperationQueue.mainQueue())
    return session
    }()


override func awakeFromNib() {
    super.awakeFromNib()
    // Initialization code

    }

func startDownload() {

    lblSongName.text = song.songName

    if self.task != nil {
        return
    }
    let url = NSURL(string: song.songDownloadLink)!
    let req = NSMutableURLRequest(URL: url)
    let task = self.session.downloadTaskWithRequest(req)
    self.task = task
    task.resume()

}

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten writ: Int64, totalBytesExpectedToWrite exp: Int64) {
    taskTotalBytesWritten = Int(writ)
    taskTotalBytesExpectedToWrite = Int(exp)
    percentageWritten = Float(taskTotalBytesWritten) / Float(taskTotalBytesExpectedToWrite)
    progressBar.progress = percentageWritten
    progressCount.text = String(Int(percentageWritten*100)) + "%"

    print("(\(taskTotalBytesWritten) / \(taskTotalBytesExpectedToWrite))")
}

func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
    if error != nil {
        print("Completed with error: \(error)")
    }
}

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

    do {
    let documentsDirectoryURL =  NSFileManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first as NSURL!
    progressCount.text = "Done!"
    progressBar.progress = 100.0

    try NSFileManager().moveItemAtURL(location, toURL: documentsDirectoryURL.URLByAppendingPathComponent(song.songName + ".mp3"))

        //Handling Badge Values
        let tabBar = UIApplication.sharedApplication().keyWindow?.rootViewController as! UITabBarController
        let downloadVC = tabBar.viewControllers?[1] as! DownloadViewController
        let badgeValue = Int(downloadVC.tabBarItem.badgeValue!)! - 1
        downloadVC.tabBarItem.badgeValue = String(badgeValue)

        if badgeValue == 0 {
            downloadVC.tabBarItem.badgeValue = nil
        }

    } catch {
        print("Error occurred during saving.")
        progressCount.text = String(error)

    }

}

}

Answer 1

也许你应该实现uitableviewcell的prepareForReuse功能？如果重用这些单元格，它们仍然可能有任务，因此startDownload在开始时返回。此外，进度条的值不会重置为0.

swift iOS - NSURLSession无法正确下载多个文件

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