在 iOS Playground 上使用 AVFoundation 的 Recorder，但 recorder.record() 总是返回 false

Question

无论如何可以在iOS游乐场上使用录音机吗？运行时，它会请求我允许使用麦克风，并且录音机实例似乎可以工作，但是，我无法使用 record(( 函数。我当前的环境是 iOS 12.1.4 和 Swift 4.2。

import UIKit
import PlaygroundSupport
import AVFoundation
class VolumnMeterViewController : UIViewController, AVAudioRecorderDelegate {
    let temporaryDirectoryToKeepRecords = FileManager.default.temporaryDirectory
    var recordButton = UIButton()
    let backgroundView = UIView()
    var recordNumber = 1
    //    var recordingSession: AVAudioSession!
    var recorder: AVAudioRecorder!
    override func loadView() {
        backgroundView.backgroundColor = #colorLiteral(red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0)
        recordButton.setTitle("Record", for: [])
        recordButton.setTitleColor(#colorLiteral(red: 0.9254902005, green: 0.2352941185, blue: 0.1019607857, alpha: 1), for: [])
        recordButton.addTarget(self, action: #selector(recordButtonTapped), for: .touchUpInside)
        recordButton.translatesAutoresizingMaskIntoConstraints = false
        backgroundView.addSubview(recordButton)
        temporaryDirectoryToKeepRecords
        self.view = backgroundView
        NSLayoutConstraint.activate([
            recordButton.widthAnchor.constraint(equalToConstant: 200),
            recordButton.heightAnchor.constraint(equalToConstant: 60),
            recordButton.centerXAnchor.constraint(equalTo: backgroundView.centerXAnchor),
            recordButton.centerYAnchor.constraint(equalTo: backgroundView.centerYAnchor)
            ])
    }
    @objc func recordButtonTapped() {
        if recorder == nil {
            recordNumber += 1
            let recordFileName = temporaryDirectoryToKeepRecords.appendingPathComponent("record(recordNumber).m4a")
            recordButton.setTitle("Stop", for: [])
            let settings = [AVFormatIDKey: Int(kAudioFormatMPEG4AAC), AVSampleRateKey: 44100, AVNumberOfChannelsKey: 1, AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue]
            do {
                let recorder = try AVAudioRecorder(url: recordFileName, settings: settings)
                // ❗️❗️❗️ Here's the problem. It always return false, assuming to be true.
                recorder.record()
            } catch {
                print(error)
            }
        } else {
            recordButton.setTitle("Record", for: [])
            recorder.stop()
            recorder = nil
        }
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = VolumnMeterViewController()

或者有没有办法跟踪麦克风音量，而不是通过录音，而只是实时检测，而不存储录音文件？多谢！

Answer 1

最后是 iOS Playground 的工作代码，非常感谢 AtulParmar！

import UIKit
import PlaygroundSupport
import AVFoundation
class VolumnMeterViewController : UIViewController, AVAudioRecorderDelegate {
    var recordingSession: AVAudioSession!
    let temporaryDirectoryToKeepRecords = FileManager.default.temporaryDirectory
    var recordButton = UIButton()
    let backgroundView = UIView()
    var playButton = UIButton()
    var recordNumber = 1
    var player: AVAudioPlayer!
    var recorder: AVAudioRecorder!
    override func loadView() {
        backgroundView.backgroundColor = #colorLiteral(red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0)
        recordButton.setTitle("Start Recording", for: [])
        recordButton.setTitleColor(#colorLiteral(red: 0.9254902005, green: 0.2352941185, blue: 0.1019607857, alpha: 1), for: [])
        recordButton.addTarget(self, action: #selector(recordButtonTapped), for: .touchUpInside)
        recordButton.translatesAutoresizingMaskIntoConstraints = false
        backgroundView.addSubview(recordButton)
        playButton.setTitle("Play Record", for: [])
        playButton.setTitleColor(#colorLiteral(red: 0.2196078449, green: 0.007843137719, blue: 0.8549019694, alpha: 1), for: [])
        playButton.addTarget(self, action: #selector(playButtonTapped), for: .touchUpInside)
        playButton.translatesAutoresizingMaskIntoConstraints = false
        backgroundView.addSubview(playButton)
        self.view = backgroundView
        NSLayoutConstraint.activate([
            recordButton.widthAnchor.constraint(equalToConstant: 200),
            recordButton.heightAnchor.constraint(equalToConstant: 60),
            recordButton.centerXAnchor.constraint(equalTo: backgroundView.centerXAnchor),
            recordButton.centerYAnchor.constraint(equalTo: backgroundView.centerYAnchor, constant: -50),
            playButton.widthAnchor.constraint(equalToConstant: 200),
            playButton.heightAnchor.constraint(equalToConstant: 60),
            playButton.centerXAnchor.constraint(equalTo: backgroundView.centerXAnchor),
            playButton.centerYAnchor.constraint(equalTo: backgroundView.centerYAnchor, constant: 50)
            ])
    }
    @objc func recordButtonTapped() {
        if recorder == nil {
            recordNumber += 1
            let recordFileName = temporaryDirectoryToKeepRecords.appendingPathComponent("record(recordNumber).m4a")
            recordButton.setTitle("Stop Rocording", for: [])
            let settings = [AVFormatIDKey: Int(kAudioFormatMPEG4AAC), AVSampleRateKey: 44100, AVNumberOfChannelsKey: 1, AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue]
            recordingSession = AVAudioSession.sharedInstance()
            do {
                try recordingSession.setCategory(.playAndRecord, mode: .default)
                try recordingSession.setActive(true, options: [])
                recorder = try AVAudioRecorder(url: recordFileName, settings: settings)
                recorder.record()
            } catch {
                print(error)
            }
        } else {
            recordButton.setTitle("Start Recording", for: [])
            recorder.stop()
            recorder = nil
        }
    }
    @objc func playButtonTapped() {
        if player == nil {
            let recordFileName = temporaryDirectoryToKeepRecords.appendingPathComponent("record(recordNumber).m4a")
            do {
                try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default)
                try AVAudioSession.sharedInstance().setActive(true)
                player = try AVAudioPlayer(contentsOf: recordFileName)
                player.play()
                playButton.setTitle("Stop Playing", for: [])
            } catch let error {
                print(error)
            }
        } else {
            player = nil
            playButton.setTitle("Play Record", for: [])
        }
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = VolumnMeterViewController()