Audiokit - 应用程序来自背景时随机崩溃

Question

我已经开始尝试使用AudioKit - 可爱的框架,但是我遇到了一些我无法追踪的崩溃.

为了开始,我想构建一个音序器,我在这个媒体帖子中跟随了这个例子:https://medium.com/@oleary.audio/building-a-midi-sequence-in-swift-bed5f5c2bb7d并且还添加了一些使用回调工具(如此处所述:AudioKit ios AKSamplerMetronome)帮助可视化在音序器中播放的当前步骤的代码.

当我在应用程序中时,一切运行正常,但是如果我退出并在后台退出应用程序并重新进入,则随机(每4-5次尝试一次)崩溃,堆栈跟踪我不明白(请参阅下面)

我不确定是什么导致这个,或者可能调用我在调试器中看到的AKMIDIInstrument.enableMIDI函数.任何提示都非常感谢.

编辑:我必须补充说,这只发生在物理设备上,我无法在模拟器中重现它.

编辑2:我也尝试将回调乐器的回调函数移到视图控制器之外,并设置一个委托来更改视图,认为视图控制器的生命周期可能会以某种方式影响它,但问题仍然存在.

这是我的代码的简化版本供参考:

class AudioCore {
    static let sharedInstance = AudioCore()
    let osc = AKOscillatorBank()
    let sequencer = AKSequencer()
    let callbackTrack:AKMusicTrack?
    let soundTrack:AKMusicTrack?
    let callbackInstrument = AKCallbackInstrument()
    let midi = AKMIDI()

    init() {
        let midiNode = AKMIDINode(node: osc)
        AudioKit.output = midiNode
        do {
            try AudioKit.start()
        }
        catch {
            AKLog("Audio kit failed to start")
        }

        if let track = sequencer.newTrack(){
            callbackTrack = track
            callbackTrack?.setMIDIOutput(callbackInstrument.midiIn)
        } else {
            callbackTrack = nil
        }

        if let sound = sequencer.newTrack(){
            soundTrack = sound
            soundTrack?.setMIDIOutput(midiNode.midiIn)
        } else {
            soundTrack = nil
        }
    }
}

class ViewController: UIViewController {
    override func viewDidLoad() {
         super.viewDidLoad()
         for i in 0...10 {
            AudioCore.sharedInstance.soundTrack?.add(noteNumber: MIDINoteNumber(pitch), velocity: 127, position: AKDuration(beats: pos), duration: AKDuration(beats: dur))
            AudioCore.sharedInstance.callbackTrack?.add(noteNumber: MIDINoteNumber(i), velocity: 127, position: AKDuration(beats: pos), duration: AKDuration(beats: dur))
         }
         AudioCore.sharedInstance.callbackInstrument.callback = { status, note, vel in
             guard status == .noteOn else { return }
             DispatchQueue.main.async {
                if(note < self.buttons.count) {
                    self.buttons[note].backgroundColor = UIColor.red
                 }
             }

             let dispatchDelay = 1.0 / tempo * 60.0 * noteLength
             DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + dispatchDelay, execute: {
                 if(note < self.buttons.count) {
                    self.buttons[note].backgroundColor = oldColor
                 }
             })
         }
    }
}