ios - AVAudioSequencer 导致 Deinit/Segue 崩溃 : 'required condition is false: outputNode'

Question

只要对象被取消初始化(例如，执行展开转场回到另一个 ViewController 时)，以下代码就会导致崩溃并出现以下错误:

required condition is false: [AVAudioEngineGraph.mm:4474:GetDefaultMusicDevice: (outputNode)]

Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: outputNode'

AVAudioSequencer 是问题的根源，因为如果删除它，错误就会停止。

如何避免这种崩溃？

class TestAudioClass {
    
    private var audioEngine: AVAudioEngine
    private var sampler: AVAudioUnitSampler
    private var sequencer: AVAudioSequencer
    
    init() {
        self.audioEngine = AVAudioEngine()
        self.sampler = AVAudioUnitSampler()
        audioEngine.attach(sampler)
        audioEngine.connect(sampler, to: audioEngine.mainMixerNode, format: nil)
        self.sequencer = AVAudioSequencer(audioEngine: audioEngine)
        if let fileURL = Bundle.main.url(forResource: "TestMusic", withExtension: "mid") {
            do {
                try sequencer.load(from: fileURL, options: AVMusicSequenceLoadOptions())
            } catch {
                print("Error loading sequencer: \(error.localizedDescription)")
            }
        }
        sequencer.prepareToPlay()
    }
}

Answer 1

此崩溃可能会令人困惑，并且如果尚未加载定序器的内容，也可能不会向控制台输出任何错误消息。非常没有帮助!

AVAudioSequencer 确实是问题的原因。要修复此问题，请使定序器成为隐式解包可选(即向其类型添加 !)，并添加显式指令以在 deinit 期间、之前 对象的其余部分被取消初始化。

固定代码如下(特别注意deinit方法):

class TestAudioClass {

    private var audioEngine: AVAudioEngine
    private var sampler: AVAudioUnitSampler
    private var sequencer: AVAudioSequencer!

    init() {
        self.audioEngine = AVAudioEngine()
        self.sampler = AVAudioUnitSampler()
        audioEngine.attach(sampler)
        audioEngine.connect(sampler, to: audioEngine.mainMixerNode, format: nil)
        self.sequencer = AVAudioSequencer(audioEngine: audioEngine)
        if let fileURL = Bundle.main.url(forResource: "TestMusic", withExtension: "mid") {
            do {
                try sequencer.load(from: fileURL, options: AVMusicSequenceLoadOptions())
            } catch {
                print("Error loading sequencer: \(error.localizedDescription)")
            }
        }
        sequencer.prepareToPlay()
    }

    deinit {
        sequencer.stop()
        sequencer = nil
    }
}

希望这有帮助!