Swift AVAudioEngine 崩溃：播放器在断开连接状态下启动

因此，我下面的代码应该以更高的音调一遍又一遍地重播 chimes.wav 文件，但由于底部的错误而崩溃。谁能找到导致此错误的原因吗？

import UIKit
import AVFoundation
class aboutViewController: UIViewController {


    var audioEngine: AVAudioEngine = AVAudioEngine()
    var audioFilePlayer: AVAudioPlayerNode = AVAudioPlayerNode()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.



        var timePitch = AVAudioUnitTimePitch()
        timePitch.pitch = 2000
        let filePath: String = NSBundle.mainBundle().pathForResource("chimes", ofType: "wav")!
        let fileURL: NSURL = NSURL(fileURLWithPath: filePath)!
        let audioFile = AVAudioFile(forReading: fileURL, error: nil)
        let audioFormat = audioFile.processingFormat
        let audioFrameCount = UInt32(audioFile.length)
        let audioFileBuffer = AVAudioPCMBuffer(PCMFormat: audioFormat, frameCapacity: audioFrameCount)
        audioFile.readIntoBuffer(audioFileBuffer, error: nil)

        var mainMixer = audioEngine.mainMixerNode
        audioEngine.attachNode(audioFilePlayer)
        audioEngine.attachNode(timePitch)
        audioEngine.connect(audioFilePlayer, to:mainMixer, format: audioFileBuffer.format)
        audioEngine.connect(timePitch, to: audioEngine.outputNode, format: audioFile.processingFormat)


        audioEngine.startAndReturnError(nil)

        audioFilePlayer.play()

        audioFilePlayer.scheduleFile(audioFile, atTime: nil, completionHandler: nil)
        audioFilePlayer.scheduleBuffer(audioFileBuffer, atTime: nil, options:.Loops, completionHandler: nil)

    }

2014-11-10 18:34:37.746 WindChimes[2350:108235] **** 由于未捕获的异常“com.apple.coreaudio.avfaudio”而终止应用程序，原因：“播放器在处于断开连接状态时启动” **** 首先抛出调用堆栈： (0x185f01e48 0x1965f40e4 0x185f01d08 0x1848726c0 0x18489a33c 0x18489975c 0x10009e638 0x10009e858 0x18a6b0e84 0x18a6b0b94 0 x18a853ad4 0x18a765310 0x18a7650dc 0x18a76505c 0x18a6ada2c 0x18a005994 0x18a000564 0x18a000408 0x189fffc08 0x189fff98c 0x189ff93bc 0x185eba14c 0x185eb70d8 0x185eb74b8 0x185de51f4 0x18ef7b5a4 0x18a716784 0x1000a54f8 0x1000a5538 0x196c62a08) libc++abi.dylib：以 NSException 类型的未捕获异常终止 （LLDB）

语句：“playerstartedwhenindisconnectedstate”表明连接链有问题。这意味着节点没有附加到引擎，或者节点没有正确链接在一起。因为同时附加了 audioFilePlayer 和 timePitch 节点，我的印象是问题出在这两行上：

audioEngine.connect(audioFilePlayer, to:mainMixer, format: audioFileBuffer.format)
audioEngine.connect(timePitch, to: audioEngine.outputNode, format: audioFile.processingFormat)

连接应将所有组件连接在一起：

audioFilePlayer -> timePitch -> audioEngine.mainMixerNode（或outputNode）

所以连接应该是这样的：

audioEngine.connect(audioFilePlayer, to:timePitch, format: audioFile.processingFormat)
audioEngine.connect(timePitch, to: audioEngine.outputNode, format: audioFile.processingFormat)

我希望这有帮助。