ios - AVAudioEngine() 播放不工作

Question

我正在尝试使用 Swift 中的 AVAudioEngine() 改变声音的音高。这是我的代码:

func setUpEngine() {
    let fileString = NSBundle.mainBundle().pathForResource("400", ofType: "wav")
    let url = NSURL(fileURLWithPath: fileString!)
    do {
        try audioFile = AVAudioFile(forReading: url)
        print("done")
    }
    catch{

    }
}
var engine = AVAudioEngine()
var audioFile = AVAudioFile()
var audioPlayerNode = AVAudioPlayerNode()
var changeAudioUnitTime = AVAudioUnitTimePitch()
override func viewDidLoad() {
    setUpEngine()
    let defaults = NSUserDefaults.standardUserDefaults()
    audioPlayerNode.stop()
    engine.stop()
    engine.reset()
    engine.attachNode(audioPlayerNode)
    changeAudioUnitTime.pitch = 800
    engine.attachNode(changeAudioUnitTime)
    engine.connect(audioPlayerNode, to: changeAudioUnitTime, format: nil)
    engine.connect(changeAudioUnitTime, to: engine.outputNode, format: nil)
    audioPlayerNode.scheduleFile(audioFile, atTime: nil, completionHandler: nil)
    engine.startAndReturnError(nil)
    audioPlayerNode.play()

我的其余代码在下面(我确实关闭了括号)。 我在网上找到了大部分代码，但我在

行中遇到了错误

engine.startAndReturnError(nil)

'Value of type has no member'.

当我删除这一行时，出现以下错误:

'AVAudioPlayerNode.mm:333: Start: required condition is false: _engine->IsRunning() Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: _engine->IsRunning()''

如有任何帮助，我们将不胜感激。我在 xCode 和单一 View 应用程序中使用 Swift。

Answer 1

错误是引擎没有运行。你需要像这样重新排序你的操作......

setUpEngine()
let defaults = NSUserDefaults.standardUserDefaults()
engine.attachNode(audioPlayerNode)
engine.attachNode(changeAudioUnitTime)
engine.connect(audioPlayerNode, to: changeAudioUnitTime, format: nil)
engine.connect(changeAudioUnitTime, to: engine.outputNode, format: nil)
changeAudioUnitTime.pitch = 800
engine.prepare()    
engine.start()    
audioPlayerNode.scheduleFile(audioFile, atTime: nil, completionHandler: nil)
audioPlayerNode.play()

一段时间后...

engine.stop()