How can I make speech occur immediately for each iteration of a while loop in Swift?

Question

Here is my playground code:

import AVFoundation


var speechsynth: AVSpeechSynthesizer = AVSpeechSynthesizer()
let wordsToSpeak = ["word one","word two","word three","word four"]

let endTime = NSDate().dateByAddingTimeInterval(10)

while endTime.timeIntervalSinceNow > 0 { 

    //workaround for iOS8 Bug

    var beforeSpeechString : String = " "
    var beforeSpeech:AVSpeechUtterance = AVSpeechUtterance(string: beforeSpeechString)
    speechsynth.speakUtterance(beforeSpeech)

    //realstring to speak
    var speechString: String = wordsToSpeak[0]

    var nextSpeech:AVSpeechUtterance = AVSpeechUtterance(string: speechString)
    nextSpeech.voice = AVSpeechSynthesisVoice(language: "en-US")
    nextSpeech.rate = AVSpeechUtteranceMinimumSpeechRate
    speechsynth.speakUtterance(nextSpeech)
}

Currently, the speaking starts AFTER the while loop completes.

How can I make it speak DURING each iteration and finish speaking before moving on to the next iteration of the loop?

Answer 1

Treat each word as a task, trigger the next task in Delegate's didFinishSpeechUtterance method.

import UIKit
import AVFoundation

class ViewController: UIViewController, AVSpeechSynthesizerDelegate {

    var queue: dispatch_queue_t = dispatch_queue_create(
        "com.test.whatever.queue", DISPATCH_QUEUE_SERIAL)
    var index: Int = 0
    let words: [String] = ["word one","word two","word three","word four"]
    var speechsynth: AVSpeechSynthesizer = AVSpeechSynthesizer()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        speechsynth.delegate = self
        self.speechCurrentWord()
    }

    func speechCurrentWord(){
        dispatch_async(queue, { () -> Void in
            var beforeSpeechString : String = " "
            var beforeSpeech:AVSpeechUtterance = AVSpeechUtterance(string: beforeSpeechString)
            self.speechsynth.speakUtterance(beforeSpeech)

            var nextSpeech:AVSpeechUtterance = AVSpeechUtterance(string: self.words[self.index])
            nextSpeech.voice = AVSpeechSynthesisVoice(language: "en-US")
            nextSpeech.rate = AVSpeechUtteranceMinimumSpeechRate
            self.speechsynth.speakUtterance(nextSpeech)
        })
    }

    func speechSynthesizer(synthesizer: AVSpeechSynthesizer!, didFinishSpeechUtterance utterance: AVSpeechUtterance!) {
        index++
        if index < self.words.count {
            self.speechCurrentWord()
        }
    }
}