堆栈视图的子视图未正确更新

Question

我正在开发一个测验应用程序，并具有一个由一系列非按钮组成的stackview。数组中按钮的数量取决于从函数Int产生的presentQuestion值，该值由与一个问题相关的答案选择的数量决定（例如：一个问题可以有3个可能的选择，另外2或5，依此类推）。

最初将QuizController加载到视图层次结构中时，显示的按钮数量正确。但是，一旦用户选择了正确的按钮，就会显示另一个视图控制器，然后用户将回到QuizController，并且再次加载视图时，将显示错误数量的按钮。

这是初始QuizController的样子（显示正确的按钮数量）：

下面是出现第二个问题后QuizController的外观（显示额外的按钮，并显示上一个问题的答案选项）：

这是QuizController的代码：

class QuizController: UIViewController {

    var questionChoices = [UIButton]()

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        choicesView.addSubview(buttonStack)

        // Function call that presents question
        let answer = questionData.presentQuestion(view: choicesView, label: questionLabel, buttons: questionChoices)

        var correctAnswer = answer.answerNum
        var answerChoices = answer.options
        var bCount = answer.buttonCount

        // Int variables for customizing buttons
        var x = 0
        var y = 1
        var z = 1

        for _ in (1...bCount) {

            questionChoices.append(UIButton())
            questionChoices[x].translatesAutoresizingMaskIntoConstraints = false
            questionChoices[x].layer.cornerRadius = 17.5
            questionChoices[x].titleLabel?.font = UIFont(name: "AvenirNext-Bold", size: 18)
            questionChoices[x].tag = y

            if questionChoices[x].tag == correctAnswer {
                questionChoices[x].setTitle(answerChoices[0], for: .normal)
                print("The right answer is \(questionChoices[x].titleLabel?.text) | button: \(questionChoices[x].tag)")
            }

            else {
                questionChoices[x].setTitle(answerChoices[z], for: .normal)
                z += 1
            }

            print((questionChoices[x].titleLabel?.text)!)

            x += 1
            y += 1
        }

        for choice in questionChoices {

            buttonStack.addArrangedSubview(choice)
            choice.translatesAutoresizingMaskIntoConstraints = false
            choice.backgroundColor = UIColor.orange
            choice.heightAnchor.constraint(equalTo: self.choicesView.heightAnchor, multiplier: 0.1275).isActive = true
            choice.addTarget(self, action: #selector(checkAnswer), for: .touchUpInside)

        }

    }
}