ViewController.swift

import UIKit
import AVFoundation

// [iOS]ボイスレコーダーアプリを作る - Qiita
// https://qiita.com/army_sh/items/946aa15263a6d087a99c

class ViewController: UIViewController {

    private enum State {
        case idle
        case recording
        case playing
    }

    @IBOutlet weak var statusLabel: UILabel!
    @IBOutlet weak var recordButton: UIButton!
    @IBOutlet weak var playButton: UIButton!

    var audioRecorder: AVAudioRecorder!
    var audioPlayer: AVAudioPlayer!

    private var status: State = .idle

    @IBAction func didTapRecordButton(_ sender: Any) {
        switch status {
        case .idle:
            let session = AVAudioSession.sharedInstance()
            try! session.setCategory(.playAndRecord)
            try! session.setActive(true)

            let settings = [
                AVFormatIDKey: Int(kAudioFormatMPEG4AAC),
                AVSampleRateKey: 44100,
                AVNumberOfChannelsKey: 2,
                AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue
            ]

            audioRecorder = try! AVAudioRecorder(url: getURL(), settings: settings)
            audioRecorder.delegate = self
            audioRecorder.record()

            status = .recording
        case .recording:
            audioRecorder.stop()
            status = .idle
        case .playing:
            break
        }

        updateUI()
    }

    private func getURL() -> URL {
        let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        let docsDirect = paths[0]
        return docsDirect.appendingPathComponent("recording.m4a")
    }

    @IBAction func didTapPlayButton(_ sender: Any) {
        switch status {
        case .idle:
            audioPlayer = try! AVAudioPlayer(contentsOf: getURL())
            audioPlayer.delegate = self
            audioPlayer.play()

            status = .playing
        case .playing:
            audioPlayer.stop()
            status = .idle
        case .recording:
            break
        }

        updateUI()
    }

    private func updateUI() {
        statusLabel.text = {
            switch status {
            case .idle:
                return "待機中"
            case .recording:
                return "録音中"
            case .playing:
                return "再生中"
            }
        }()

        recordButton.setTitle(
            {
                switch status {
                case .idle, .playing:
                    return "RECORD"
                case .recording:
                    return "STOP"
                }
            }(),
            for: .normal
        )

        recordButton.isEnabled = {
            switch status {
            case .idle, .recording:
                return true
            case .playing:
                return false
            }
        }()

        playButton.setTitle(
            {
                switch status {
                case .idle, .recording:
                    return "PLAY"
                case .playing:
                    return "STOP"
                }
            }(),
            for: .normal
        )

        playButton.isEnabled = {
            switch status {
            case .idle, .playing:
                return true
            case .recording:
                return false
            }
        }()
    }
}

extension ViewController: AVAudioRecorderDelegate {

}

extension ViewController: AVAudioPlayerDelegate {

}