问AKMIDIListener:无法更改UI组件的ReceivedNoteOn

EN

let midi = AudioKit.midi


class firstPageViewController: UIViewController, AKMIDIListener {

@IBOutlet var MusicButtons: [UIButton]!
@IBOutlet var playButton: UIButton!
@IBOutlet var pauseButton: UIButton!
@IBOutlet var WaveForm: AudioVisualizationView!


@IBOutlet weak var firstButton: UIButton!

@IBOutlet weak var secondButton: UIButton!

@IBOutlet weak var thirdButton: UIButton!


override func viewDidLoad() {
    super.viewDidLoad()
    isOnFirstPage = true
    isOnSecondPage = false
    isOnThirdPage = false
    self.secondButton.setTitleColor(UIColor.blue, for: .normal)
    self.thirdButton.setTitleColor(UIColor.blue, for: .normal)
    midi.openInput()
    midi.addListener(self)
    self.init_buttons()
    self.init_soundwave()
    self.init_audio()
}

func receivedMIDINoteOn(noteNumber: MIDINoteNumber, velocity: MIDIVelocity, channel: MIDIChannel) {
    let currNum = mapping[Int(noteNumber)]
    if currNum == 64 { //Play button
        self.playBackground(0)
        self.playButton.setTitle("Currently Playing", for: .normal)
    }
    else if currNum == 67 { //Pause button
        self.pauseMusic(0)
        self.playButton.setTitle("Play", for: .normal)
    }
    else if currNum == 68 { //Switch button - first page
        self.firstPageSwitch(0)
    }
    else if currNum == 69 { //Switch button - second page
        self.secondPageSwitch(0)
    }
    else if currNum == 70 { //Switch button - third page
        self.thirdPageSwitch(0)
    }
    else if currNum == 71 {
        //
    }
    else if currNum == 65 {
        //
    }
    else if currNum == 66 {
        //
    }
    else {
        if isOnFirstPage! {
            self.playMusic(currNum: currNum!, holder: audioPlayer)
            self.MusicButtons![currNum!].backgroundColor = UIColor(red: 247/255, green: 183/255, blue: 98/255, alpha: 1.0)
        }
        if isOnSecondPage!{
            self.playMusic(currNum: currNum!, holder: secondAudioPlayer)
            self.MusicButtons![currNum!].backgroundColor = UIColor(red: 247/255, green: 183/255, blue: 98/255, alpha: 1.0)
        }
    }
}