ios - 如何在 Swift 中的 while 循环的每次迭代中立即进行语音？

Question

这是我的游乐场代码：

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)
}

目前，演讲在 while 循环完成后开始。

我怎样才能让它在每次迭代期间说话并在继续循环的下一次迭代之前完成说话？

Answer 1

将每个单词视为一个任务，在 Delegate 的 didFinishSpeechUtterance 方法中触发下一个任务。

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()
        }
    }
}