初始化之前使用的常量'錯誤'

Question

我正在檢測麥克風打擊並使用它觸發動畫並獲取此錯誤消息。在初始化之前使用「常量」錯誤「。這是我的代碼：

override func viewDidLoad() { 
    super.viewDidLoad() 

    //make an AudioSession, set it to PlayAndRecord and make it active 
    let audioSession:AVAudioSession = AVAudioSession.sharedInstance() 
    try! audioSession.setCategory(AVAudioSessionCategoryRecord) 
    try! audioSession.setActive(true) 

    //set up the URL for the audio file 
    let documents: AnyObject = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)[0] as AnyObject 
    let str = (documents as! NSString).appending("recordTest.caf") 
    NSURL.fileURL(withPath: str as String) 


    // make a dictionary to hold the recording settings so we can instantiate our AVAudioRecorder 
    let recordSettings: [NSObject : AnyObject] = [AVFormatIDKey as NSObject:kAudioFormatAppleIMA4 as AnyObject, 
                AVSampleRateKey as NSObject:44100.0 as AnyObject, 
                AVNumberOfChannelsKey as NSObject:2 as AnyObject,AVEncoderBitRateKey as NSObject:12800 as AnyObject, 
                AVLinearPCMBitDepthKey as NSObject:16 as AnyObject, 
                AVEncoderAudioQualityKey as NSObject:AVAudioQuality.max.rawValue as AnyObject 

    ] 

    //declare a variable to store the returned error if we have a problem instantiating our AVAudioRecorder 
    let error: NSError? 

    //Instantiate an AVAudioRecorder 
    recorder = try! AVAudioRecorder(url: documents as! URL, settings: recordSettings as! [String : Any]) 

    //If there's an error, print it - otherwise, run prepareToRecord and meteringEnabled to turn on metering (must be run in that order) 
    if let e = error { 
     print(e.localizedDescription) 
    } else { 
     recorder.prepareToRecord() 
     recorder.isMeteringEnabled = true 

     //start recording 
     recorder.record() 

     //instantiate a timer to be called with whatever frequency we want to grab metering values 
     self.levelTimer = Timer.scheduledTimer(timeInterval: 0.02, target: self, selector: #selector(ViewController.levelTimerCallback), userInfo: nil, repeats: true) 

    } 

} 

//selector/function is called every time our timer (levelTime) fires 
func levelTimerCallback() { 
    //update meters 
    recorder.updateMeters() 

    //print to the console if we are beyond a threshold value 
    if recorder.averagePower(forChannel: 0) > -7 { 
     print("Mic Blow Detected ") 
     print(recorder.averagePower(forChannel: 0)) 
     isAnimating = false 
    } else { 
     isAnimating = true 
    } 
} 

它還看來，這個線是迫使應用程序退出所以顯然這是哪裏的問題，但我是新來的Xcode和不能當場我做了什麼錯，如果任何人都有想法，我應該改變這一點，這將是偉大的。

recorder = try! AVAudioRecorder(url: documents as! URL, settings: recordSettings as! [String : Any]) 

在此先感謝！

Answer 1

您沒有可以在聲明點和使用點之間設置值error的代碼。對於錯誤可能會帶來一個新值，它將不得不被傳遞給AVAudioRecorder的構造函數。因爲沒有機會爲它的值來改變

let error : Error? = nil

但同樣，這將是輕浮（它是一個let變量），甚至如果它是一個變種，它不是：你可以初始化錯誤傳遞給任何代碼，當它被宣佈時，以及它在if let建設中使用。

由於您已告知系統您要創建AVAudioRecorder，但它永遠不會失敗（即try!），您將會崩潰。更有可能你想做類似的事情：

let documentSearchPaths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true) 
let documentsDir = documentSearchPaths[0] as NSString 
let recordingFilePath = documentsDir.appendingPathComponent("recordTest.caf") 
let recordingFileURL = NSURL.fileURL(withPath: recordingFilePath) 

var recorder : AVAudioRecorder? 
do{ 
    let audioSession = AVAudioSession.sharedInstance() 
    try audioSession.setCategory(AVAudioSessionCategoryRecord) 
    try audioSession.setActive(true) 

    // make a dictionary to hold the recording settings so we can instantiate our AVAudioRecorder 
    let recordSettings: [String : Any] = [AVFormatIDKey : kAudioFormatAppleIMA4, 
              AVSampleRateKey : NSNumber(value: 44100.0), 
              AVNumberOfChannelsKey : NSNumber(value: 2), 
              AVEncoderBitRateKey : NSNumber(value: 12800), 
              AVLinearPCMBitDepthKey : NSNumber(value: 16), 
              AVEncoderAudioQualityKey :NSNumber(value: AVAudioQuality.max.rawValue) 
    ] 

    recorder = try AVAudioRecorder(url: recordingFileURL, settings: recordSettings) 
} catch let audio_error as NSError { 
    print("Setting up the audio recording failed with error \(audio_error)") 
} 

if let recorder = recorder { 
    recorder.prepareToRecord() 
    recorder.isMeteringEnabled = true 

    //start recording 
    recorder.record() 

    //etc... 
}