arrays - 展开可选值时发现 nil(音乐库)

Question

var songList = NSMutableArray()
var player = AVPlayer()
var isSelected = false

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.



    var songs = MPMediaQuery() // also tried var songs = MPMediaQuery.songsQuery()
    var localSongs: NSArray = songs.items
    songList = NSMutableArray(array: localSongs)

    tableView.reloadData()

    var song: MPMediaItem = songList[0] as MPMediaItem // <<- Error here

    var currentItem = AVPlayerItem(URL: song.valueForProperty(MPMediaItemPropertyAssetURL) as NSURL)

    player.replaceCurrentItemWithPlayerItem(currentItem)

    player.play()

    var songTitle: NSString = song.valueForProperty(MPMediaItemPropertyTitle) as NSString

    songName.text = songTitle 

    var time = Float(CMTimeGetSeconds(player.currentItem.duration))
    sliderOutlet.value = time




}

我正在构建一个音乐播放器，但是当我在模拟器中运行时应用程序崩溃并给出了这个错误:index 0 beyond bounds for empty array，当我尝试在 iPhone 上运行时说这个:{

MediaLibrary} Database validation succeeded
fatal error: unexpectedly found nil while unwrapping an Optional value

编辑:似乎它没有访问我的 iPhone 上的本地音乐库并将歌曲添加到阵列。

Answer 1

您正在访问一个元素而没有测试它的大小。所以 songList[0] 越界，因此崩溃。