Storyboard segue 导致 AVAudioEngine 崩溃

Question

我正在使用附加到我的应用程序中的 AVAudioEngine 的 AVAudioUnitSampler。我已经让一切正常工作，除了当我从视图控制器中分离出采样器被实例化的时候。我遇到了一个错误，上面写着：

由于未捕获的异常“com.apple.coreaudio.avfaudio”而终止应用程序，原因：“所需条件为假：outputNode”

我猜这是因为当我转回到我以前的 VC 时引擎以某种方式中断，不确定！

我已尝试停止引擎以及 viewWillDisappear 中的排序器，但它仍然崩溃。

如果我对以前的 VC 使用 UIButton show segue，它可以工作，但我会因展开 segue 和当前导航栏 segue 而崩溃。

我是新手，所以希望我已经解释得足够清楚了！

我从前一个 VC 上的表视图触发的 segue 进入这个 VC。

这里是有问题的 VC 的代码：

import UIKit
import AVFoundation

class PlayerViewController: UIViewController {
    @IBOutlet weak var descriptionLabel: UILabel!
    @IBOutlet weak var playPauseButton: UIButton!
    @IBOutlet weak var musicView: UIImageView!

    let allSounds = SoundBankOnAndOff()
    var currentSoundFile: OnandOff?
    var engine = AVAudioEngine()
    var sampler = AVAudioUnitSampler()

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(true)

        self.navigationController?.isNavigationBarHidden = false
        setupSequencer()
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(true)
        engine.stop()
        sequencer.stop()
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        descriptionLabel.text = exercises[myIndex]
        musicView.image = musicNotes[myIndex]
        engine = AVAudioEngine()
        sampler = AVAudioUnitSampler()

        engine.attach(sampler)
        engine.connect(sampler, to: engine.mainMixerNode, format: nil)
        loadSF2PresetIntoSampler(preset: 0)
        startEngine()
        setSessionPlayback()
    }

    func setSessionPlayback() {
        let audioSession = AVAudioSession.sharedInstance()
        do {
            try
                audioSession.setCategory(AVAudioSessionCategoryPlayback, with:
                    AVAudioSessionCategoryOptions.mixWithOthers)
        } catch {
            print("couldn't set category \(error)")
            return
        }

        do {
            try audioSession.setActive(true)
            print("category is active")
        } catch {
            print("couldn't set category to active \(error)")
            return
        }
    }

    func startEngine() {
        if engine.isRunning {
            print("audio engine has already started")
            return
        }

        do {
            try engine.start()
            print("audio engine started")
        } catch {
            print("oops \(error)")
            print("could not start audio engine")
        }
    }

    var sequencer:AVAudioSequencer!

    func setupSequencer() {
        let allSounds = SoundBankOnAndOff()
        let currentSoundFile = allSounds.list[myIndex]
        self.sequencer = AVAudioSequencer(audioEngine: engine)

        let options = AVMusicSequenceLoadOptions.smfChannelsToTracks

        if let fileURL = Bundle.main.urls(forResourcesWithExtension: "mid", subdirectory: "On & Off MIDI") {
            do {
                try sequencer.load(from: (currentSoundFile.soundFile), options: options)
                print("loaded \(fileURL)")
            } catch {
                print("something messed up \(error)")
                return
            }
        }
        sequencer.prepareToPlay()
    }


    func play() {
        if sequencer.isPlaying {
            stop()
        }

        sequencer.currentPositionInBeats = TimeInterval(0)

        do {
            try sequencer.start()


        } catch {
            print("cannot start \(error)")
        }
    }

    func stop() {
        sequencer.stop()
    }

    func loadSF2PresetIntoSampler(preset:UInt8)  {
        guard let bankURL = Bundle.main.url(forResource: "Pad Sounds", withExtension: "sf2") else {
            print("could not load sound font")
            return
        }

        do {
            try sampler.loadSoundBankInstrument(at: bankURL, program: preset,bankMSB: UInt8(kAUSampler_DefaultMelodicBankMSB),bankLSB: UInt8(kAUSampler_DefaultBankLSB))
        } catch {
            print("error loading sound bank instrument")
        }
    }



    @IBAction func playButtonPressed(sender: UIButton) {
        if sender.currentTitle == "PLAY"{
            play()
            sender.setTitle("STOP", for: .normal)
        } else if sender.currentTitle == "STOP" {
            sender.setTitle("PLAY", for: .normal)

            stop()
        }
    }

    @IBAction func BackButtonPressed(_ sender: Any) {
        performSegue(withIdentifier: "unwindToDetailVC", sender: self)
    }
}

Answer 1

此代码与您的代码相似，并且在 segue 或 unwinding 时不会崩溃：

class MP3PlayerVC: UIViewController {

    let audioEngine = AVAudioEngine()
    let audioPlayer = AVAudioPlayerNode()
    let distortion = AVAudioUnitDistortion()

    override func viewDidLoad() {
        super.viewDidLoad()

        audioEngine.attach(audioPlayer)
        audioEngine.attach(distortion)
        audioEngine.connect(audioPlayer, to: distortion, format: nil)
        audioEngine.connect(distortion, to: audioEngine.outputNode, format: nil)
    }

    @IBAction func buttonClicked(_ sender: UIButton) {

        if let filePath = Bundle.main.path(forResource: "test", ofType: "mp3") {

            let url = URL.init(fileURLWithPath: filePath)

            if let audioFile = try? AVAudioFile(forReading: url) {

                if audioPlayer.isPlaying {
                    audioPlayer.stop()
                    audioEngine.stop()
                } else {

                    audioPlayer.scheduleFile(audioFile, at: nil, completionHandler: nil)

                    do {
                        try audioEngine.start()

                        audioPlayer.play()

                    } catch {
                        print("something went wrong")
                    }
                }
            }
        }
    }
}