首次使用或应用程序进入后台时下载失败答案

【问题标题】：Download fails when on first use or app goes in background首次使用或应用程序进入后台时下载失败
【发布时间】：2016-11-04 12:34:31
【问题描述】：

Alamofire 3.5.0、Swift2.2

我正在使用 Alamofire 下载方法下载 ZIP 文件，我注意到当我开始下载过程并且应用程序进入后台时，下载失败并出现以下错误：

----------------------
error Optional(Error Domain=NSCocoaErrorDomain Code=4
    "“CFNetworkDownload_pZ56nc.tmp” couldn’t be moved to “courses”
    because either the former doesn't exist, or the folder containing
    the latter doesn't exist." UserInfo=
    {NSSourceFilePathErrorKey=
/private/var/mobile/Containers/Data/Application/[UUID]/tmp/CFNetworkDownload_pZ56nc.tmp, 
    NSUserStringVariant=(
        Move
    ),     
    NSDestinationFilePath=
/var/mobile/Containers/Data/Application/[UUID]/Library/courses/course_302.zip, 
    NSFilePath=
/private/var/mobile/Containers/Data/Application/[UUID]/tmp/CFNetworkDownload_pZ56nc.tmp, 
    NSUnderlyingError=0x13f52f990 {Error Domain=NSPOSIXErrorDomain
    Code=2 "No such file or directory"}})
----------------------

这是下载文件的代码：

//...
var userLibraryPath:String = {
    return NSSearchPathForDirectoriesInDomains(.LibraryDirectory, .UserDomainMask, true)[0]
}()

//...
let _coursePath:NSURL = NSURL(string: "file://\(userLibraryPath)/)")!
//...
let zipURL = _coursePath.URLByAppendingPathComponent("course_\(courseId).zip")
        //if file exists destroy it
        if let zipPath = zipURL?.path where NSFileManager.defaultManager().fileExistsAtPath(zipPath) {
            do {
                try NSFileManager.defaultManager().removeItemAtPath(zipPath)
            } catch let error as NSError {
                print(error)
            }
        }
        //
        let downloadRequest = Alamofire.download(Router.download(courseId), destination: { (url:NSURL, urlResponse:NSHTTPURLResponse) -> NSURL in
            //
            return zipURL!
            //
        }).progress({ (bytesWritten, totalBytesWritten, totalBytesExpectedToWrite) in
            //
            let progress = Double(totalBytesWritten) / Double(totalBytesExpectedToWrite)

            dispatch_async(GlobalMainQueue, {
                self.notifyDownloadProgress(courseId, progress: progress)
            })

        }).response(completionHandler: { (request:NSURLRequest?, response:NSHTTPURLResponse?, data:NSData?, error:NSError?) in
            self.removeFromQueue(courseId)
            print("response")
            print("----------------------")
            print("error \(error)")
            print("----------------------")
            //here I would try to extract it
})

更新我刚刚在 iPhone 5 全新安装的应用程序上进行了测试，它不必进入后台（例如通过主页按钮）失败，它在第一次加载时失败（以及任何后续）直到应用被杀死并重新打开。

为什么要在路径中添加“/private”位？我在这里做错了什么？

【问题讨论】：

标签： ios iphone swift2 alamofire

【解决方案1】：

确实是“没有这样的文件或目录”错误。

当我添加时：

//
let downloadRequest = Alamofire.download(Router.download(courseId), destination: { (url:NSURL, urlResponse:NSHTTPURLResponse) -> NSURL in
    let course = zipURL!.URLByDeletingLastPathComponent!.path!
    let fm = NSFileManager.defaultManager()
    var isDir:ObjCBool = false
    if(fm.fileExistsAtPath(path, isDirectory: &isDir) == false){
       //doesnt exist
       do {
           try fm.createDirectoryAtPath(path, withIntermediateDirectories: true, attributes: nil)
       } catch let error as NSError {
           //
           print(error)
       }
    }

    return zipURL!
    //
 })

【讨论】：