Swift 5：AVPlayer将多个音频文件相互叠加。

Question

我正在构建一个Swift 5音乐应用，其中一个表格视图从JSON API中加载并列出多个对象。点击一个条目后，导航器会调用所选项目的详细视图。

下面，你可以看到我的详细视图控制器，叫做 BroadcastDetailViewController. 正如你所看到的，有一个 playBroadcastButton 它将播放音频文件，并设置了 AVAudioSession.

到目前为止还不错。但在我实现了通过控制中心洗涤器擦洗音频文件的可能性(commandCenter.changePlaybackPositionCommand.addTarget)，然后回到我的表视图控制器，选择另一个项目来播放它的音频文件，AVPlayer会将多个音频文件叠加在一起并同时播放。这是我不想要的行为。在我实现控制按钮之前，整个音频文件替换过程工作正常。

我的问题是，为什么播放器会突然在另一个文件上播放另一个文件，而不是将旧的文件静音并替换成新的文件？

class BroadcastDetailViewController: UIViewController {

    var player = AVPlayer()
    var playerItem: AVPlayerItem!

    var broadcast:Broadcasts?

    @IBOutlet weak var imageView: UIImageView!
    @IBOutlet weak var titleLabel: UILabel!

    @IBAction func playBroadcastButton(_ sender: Any) {
        player.play()
        setupAVAudioSession()
    }

    private func setupAVAudioSession() {
        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSession.Category.playback)
            try AVAudioSession.sharedInstance().setActive(true)
            debugPrint("AVAudioSession is Active and Category Playback is set")
            UIApplication.shared.beginReceivingRemoteControlEvents()
            setupCommandCenter()
        } catch {
            debugPrint("Error: \(error)")
        }
    }

    private func setupCommandCenter() {

        // Meta
        var nowPlayingInfo = [String : Any]()

        nowPlayingInfo[MPMediaItemPropertyTitle] = broadcast?.title ?? "Radio Bass"
        nowPlayingInfo[MPMediaItemPropertyArtist] = "Radio Bass"
        nowPlayingInfo[MPMediaItemPropertyAlbumTitle] = "Radio Bass."
        nowPlayingInfo[MPNowPlayingInfoPropertyElapsedPlaybackTime] = playerItem.currentTime().seconds
        nowPlayingInfo[MPMediaItemPropertyPlaybackDuration] = playerItem.asset.duration.seconds
        nowPlayingInfo[MPNowPlayingInfoPropertyPlaybackRate] = player.rate

        MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingInfo

        let commandCenter = MPRemoteCommandCenter.shared()
        commandCenter.playCommand.isEnabled = true
        commandCenter.pauseCommand.isEnabled = true
        commandCenter.playCommand.addTarget { [weak self] (event) -> MPRemoteCommandHandlerStatus in
            self?.player.play()
            return .success
        }
        commandCenter.pauseCommand.addTarget { [weak self] (event) -> MPRemoteCommandHandlerStatus in
            self?.player.pause()
            return .success
        }

        // Scrubber
        commandCenter.changePlaybackPositionCommand.addTarget { event in
            let seconds = (event as? MPChangePlaybackPositionCommandEvent)?.positionTime ?? 0
            let time = CMTime(seconds: seconds, preferredTimescale: 1)
            self.player.seek(to: time)
            return .success
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        let urlAudioString = broadcast?.audio

        playerItem = AVPlayerItem(url: URL(string: urlAudioString!)!)
        player = AVPlayer(playerItem: playerItem)

        title = broadcast?.title

        let urlImageString = broadcast?.image
        let urlImage = URL(string: urlImageString!)

        titleLabel.text = broadcast?.title
        imageView.load(url: urlImage!)
    }
}

Answer 1

释放自由和停止 AVPlayer 和 AVPlayerItem 在回到表视图控制器之前

avPlayer.pause()
avPlayer.cancelPendingPrerolls() // stops network requests
avPlayer.replaceCurrentItem(with: nil)