     private let trackListButton = UIButton(type: .custom)
     
     private var audioPlayer: AVPlayer!
+    private var audioFileName: String?
+    private var audioArtistName: String?
     
     private var musicType: MusicType = .library
     
     private let volumeSlider: UISlider = {
-        return MPVolumeView().subviews.filter { $0 is UISlider }.map { $0 as! UISlider }.first!
+        let slider = MPVolumeView().subviews.filter { $0 is UISlider }.map { $0 as! UISlider }.first!
+        slider.isUserInteractionEnabled = true
+        return slider
     }()
     
     private var verticalConstraints: [NSLayoutConstraint] = []

        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
            let audioItem = AVPlayerItem(url: UIDocument(fileURL: url).presentedItemURL!)
            self.audioPlayer = AVPlayer(playerItem: audioItem)
            self.audioPlayer.play()
            self.musicType = .file

        musPickerButton.constrain(.left, .equal, to: volumeSlider, .left)
        
        icloudDocButton.constrain(.top, .equal, to: musPickerButton, .top)
        icloudDocButton.constrain(.centerX, .equal, to: albumTitleLabel, .centerX)
        
        trackListButton.constrain(.top, .equal, to: musPickerButton, .top)
        trackListButton.constrain(.right, .equal, to: volumeSlider, .right)
