Question

我试图在swift中编写一个pow函数，这是我的代码：

var recorder: AVAudioRecorder!
var levelTimer = NSTimer()
var lowPassResults: Double = 0.0

override func viewDidLoad() {
    super.viewDidLoad()
    let url = NSURL.fileURLWithPath("dev/null")
    //numbers are automatically wrapped into NSNumber objects, so I simplified that to [NSString : NSNumber]
    var settings : [NSString : NSNumber ] = [AVSampleRateKey: 44100.0, AVFormatIDKey: kAudioFormatAppleLossless, AVNumberOfChannelsKey: 1, AVEncoderAudioQualityKey: AVAudioQuality.Max.rawValue]
    var error: NSError?
    self.recorder = [[AVAudioRecorder alloc] initWithURL:soundFileURL, settings:recordSettings, error:&error];
    if((recorder) != nil){
        recorder.prepareToRecord()
        recorder.meteringEnabled = true
        recorder.record()
        levelTimer = NSTimer.scheduledTimerWithTimeInterval(0.03, target: self, selector: Selector("listenForBlow"), userInfo: nil, repeats: true)
    }
    else{
        NSLog("%@", "Fehler an dieser Stelle");
    }
}
func levelTimerCallback(timer:NSTimer) {
    recorder.updateMeters()
    let ALPHA: Double = 0.05
    var peakPowerForChannel: Double = pow(10, (0.05 * [self.recorder.peakPowerForChannel(0)]))
    lowPassResults = ALPHA * peakPowerForChannel + (1.0 - ALPHA) * lowPassResults;

    NSLog("@Average input: %f Peak input: %f Low pass results: %f", [recorder.averagePowerForChannel(0)], [recorder.peakPowerForChannel(0)], lowPassResults);
}

我在两行中遇到错误而且我不知道如何修复它们。这是此行中的第一个错误:(错误：＆＃34;预期＆＃39;，＆＃39;分隔符）。是否存在我忽略的语法错误？

self.recorder = [[AVAudioRecorder alloc] initWithURL:soundFileURL, settings:recordSettings, error:&error];

这是另一个错误：＆＃34;无法找到＆＃39; *＆＃39;接受提供的参数＆＃34;。我知道类型必须相同（Double * Double）。但确切的错误在哪里？

var peakPowerForChannel: Double = pow(10, (0.05 * [self.recorder.peakPowerForChannel(0)]))

P.S。：我知道有很多这样的问题，但我找不到快速的答案。提前谢谢!!

Answer 1

使用Swift而不是Objective-C语法来初始化录音机：

recorder = try AVAudioRecorder(URL:…settings:…)

要计算peakPowerForChannel，请知道10将是Int而peakPowerForChannel(_:)会返回Float，而不是Double。您需要明确地投射这些：

var peakPowerForChannel : Double = pow(Double(10), (0.05 * Double(recorder.peakPowerForChannel(0))))

此外，由于pow(_: _:)返回Double，您可以删除peakPowerForChannel的类型规范：

var peakPowerForChannel = pow(Double(10), (0.05 * Double(recorder.peakPowerForChannel(0))))

如何在swift中编写pow（）并修复错误？

1 个答案: