BriefDemoViewController.swift

import UIKit
// Step 1: Import AVFoundation library
import AVFoundation

class AVFoundataionDemoViewController: BaseViewController {
  var avSpeechSynthesizer: AVSpeechSynthesizer!
  
  @IBAction func startSpeechAction(_ sender: Any) {
    // Step 4: Stop any existing speech, else it will not start !!!
    avSpeechSynthesizer.stopSpeaking(at: .immediate)
    avSpeechSynthesizer.speak(AVSpeechUtterance(string: "Hello world"))
  }
  
  override func viewDidLoad() {
    super.viewDidLoad()
    // Step 2: Init AVSpeechSynthesizer, which is the controller of what to speak and the status of speech.
    avSpeechSynthesizer = AVSpeechSynthesizer()
    
    // Step 3: Assign AVSpeechSynthesizerDelegate
    avSpeechSynthesizer.delegate = self
  }
  
  override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    print("viewWillDisappear")
    
    // Step 5: stop speaking to prevent blocking of deinit
    avSpeechSynthesizer.stopSpeaking(at: .immediate)
    
    // Step 5 (alternative): stop speaking to prevent blocking of deinit
    avSpeechSynthesizer.delegate = nil
  }
  
  override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    print("viewDidDisappear")
  }
  
  deinit {
    print("AVFoundationDemoViewController is deinit.")
  }
}

extension AVFoundataionDemoViewController: AVSpeechSynthesizerDelegate {
}