在哪里放置倒数计时器代码？

Question

我正在开发一个 iOS 测验应用程序，每次提出问题时，我都希望启动一个 15 秒的倒数计时器。如果用户在计数器达到零时没有回答问题，则认为答案是错误的。我的问题是我应该在哪里放置倒数计时器代码以确保每次提出问题时它都会给用户 15 秒的时间来回答？我还希望每次提出新问题时都重置此时间。

我的代码：

class ViewController: UIViewController {
    //countdown timer
    @IBOutlet weak var questionTimer: UILabel!

    func randomQuestion() {
        //random question
        if questionList.isEmpty {
            questionList = Array(QADictionary.keys)
        }

        let rand = Int(arc4random_uniform(UInt32(questionList.count)))
        questionLabel.text = questionList[rand]

        //matching answer values to go with question keys
        var choices = QADictionary[questionList[rand]]!

        questionList.remove(at: rand)

        //create button
        var button:UIButton = UIButton()

        //variables
        var x = 1
        rightAnswerBox = arc4random_uniform(4)+1

        for index in 1...4
        {
            button = view.viewWithTag(index) as! UIButton

            if (index == Int(rightAnswerBox))
            {
                button.setTitle(choices[0], for: .normal)
            }
            else {
                button.setTitle(choices[x], for: .normal)
                x += 1
            }

            randomImage()

        }
    }

    let QADictionary = ["Who is Thor's brother?" : ["Atum", "Loki", "Red Norvell", "Kevin Masterson"], "What is the name of Thor's hammer?" : ["Mjolinr", "Uru", "Stormbreaker", "Thundara"], "Who is the father of Thor?" : ["Odin", "Sif", "Heimdall", "Balder"]]

    //wrong view segue
    func wrongSeg() {
       performSegue(withIdentifier: "wrongViewSegue", sender: self)
    }

    //proceed screen
    func rightSeg() {
        performSegue(withIdentifier: "rightSeg", sender: self)
    }

    //variables
    var rightAnswerBox:UInt32 = 0
    var index = 0

    //Question Label
    @IBOutlet weak var questionLabel: UILabel!

    //Answer Button
    @IBAction func buttonAction(_ sender: AnyObject) {
        if (sender.tag == Int(rightAnswerBox))
        {
            print ("Correct!")
        }
        else if (sender.tag != Int(rightAnswerBox)) {
            wrongSeg()
            print ("Wrong!")
            questionList = []
        }

        randomQuestion()
    }

    override func viewDidAppear(_ animated: Bool)
    {
        randomQuestion()
    }

    //variables
    var seconds = 15
    var timer = Timer()

    override func viewDidLoad() {
        super.viewDidLoad()
    }

Answer 1

这应该为您提供一些基本的构建块来构建您的解决方案。

// Timer property
var timer: Timer?


// Call this when a new question is loaded
func startTimer() {

    self.timer?.invalidate()

    self.timer = Timer.scheduledTimer(withTimeInterval: 15.0,
                                      repeats: false,
                                      block: { timer in

                                        // Put whatever code should happen if the user does not answer the question in time. 

    })
    RunLoop.main.add(timer,
                     forMode: .commonModes)

}

// Call this when a question has been answered
func questionAnswered() {

    self.timer?.invalidate()

    // Put whatever should happen if a question was answered in time here

}