为什么会出现nil错误？

Question

目前，我可以在iPhone上将当前正在播放的歌曲添加到我的应用程序中，但是我正在尝试根据应用程序上的歌曲名称从Parse播放一首歌曲，但出现了nil错误。 为什么？

 func playit(sender: UIButton!){
    if let nowPlaying = musicPlayer.nowPlayingItem{
    let title = nowPlaying[MPMediaItemPropertyTitle] as? String
    let artist = nowPlaying[MPMediaItemPropertyTitle] as? String

    println(title! + artist!)


        let query = PFQuery(className: "Songs")
        query.whereKey("SongName", equalTo: title!)
        query.findObjectsInBackgroundWithBlock {
            (objects: [AnyObject]?, error: NSError?) -> Void in
            if error == nil {
                // The find succeeded.
                println("Successfully retrieved \(objects!.count) song(s).")
                // Do something with the found objects
                if let objects = objects as? [PFObject] {
                    for object in objects {
                        println(object.objectId)

                        let objects: PFObject = object as PFObject
                        let parseAudio: PFFile = objects.valueForKey("Songs") as! PFFile
                        let audioPath: String = parseAudio.url!
                        let urlParse: NSURL = NSURL(string: audioPath)!

                        player = AVPlayer(URL: urlParse)
                        println(player)
                        player.play()
                    }
                }
            } else {
                // Log details of the failure
                println("Error: \(error!) \(error!.userInfo!)")
            }

        }

    }
}

Answer 1

不知道确切的错误是什么，我只能说您的问题很可能是在此块中：

            let objects: PFObject = object as PFObject
                    let parseAudio: PFFile = objects.valueForKey("Songs") as! PFFile
                    let audioPath: String = parseAudio.url!
                    let urlParse: NSURL = NSURL(string: audioPath)!

将parseAudio转换为NSURL的字符串不会为媒体播放器获取文件的内容。 尝试这样的事情：

let parseAudio: PFFile = objects.valueForKey("Songs") as? PFFile
parseAudio?.getDataInBackgroundWithBlock({ (data, error) -> Void in

      if error == nil {
             // do what you need to with the music file which is contained in `data`
              let fullParseAudioFile = data

      } else if error != nil {

      println(error!.localizedDescription)

      }

  })

我没有与媒体播放器一起工作，所以我不知道将数据转换为哪种格式，但是现在您将拥有可用的文件，而不仅仅是代表文件名的字符串。