ios - 使用 arc4random_uniform() 的简单测验

Question

我正在创建一个简单的测验应用程序。有四种选择，选择的位置是随机生成的。设置了四个 UILabel 以显示选项。

我写了下面的代码，它通常运行良好，但有时会显示相同的选项。

例)2017 2015 2015 1700

错误应该是 for 循环，但我想不通。

let questions = ["What year is now?"]
let answers = [["2017", "2015", "1000", "1700"]]
var rightAnswerPlacement:UInt32 = 0
var currentQuestion = 0

//Function that displays new question
func newQuestion()
{
    lbl.text = questions[currentQuestion]        
    rightAnswerPlacement = arc4random_uniform(4)+1        
    // Create a button
    var button:UIButton = UIButton()
    var x = 1        
    for i in 1...4
    {
        //Create a button
        button = view.viewWithTag(i) as! UIButton
        if (i == Int(rightAnswerPlacement))
        {
            button.setTitle(answers[currentQuestion][0], for: .normal)
        }
        else
        {
            button.setTitle(answers[currentQuestion][x], for: .normal)
            x = 2
        }
    }
    button.setTitle(answers[currentQuestion][3], for: .normal)
    currentQuestion += 1
}

Answer 1

一个非常的常用方法是“随机”答案。那么你不必做任何ifs:

let questions = [
    "What year is now?",
    "What is your favorite color?"
]

let answers = [
    ["2017", "2015", "1000", "1700"],
    ["Blue", "Red", "Yellow", "Green"]
]

var currentQuestion = 0

//Function that displays new question
func newQuestion()
{
    // get the current question text
    let thisQuestion = questions[currentQuestion]

    // get a "shuffled" array of the current answers
    let theseAnswers = answers[currentQuestion].shuffled()

    lbl.text = thisQuestion

    // loop through the shuffled answers, setting the button titles
    for (i, answer) in theseAnswers.enumerated() {
        if let button = view.viewWithTag(i) as? UIButton {
            button.setTitle(answer, for: .normal)
        }
    }

}

现在，每次调用 newQuestion() 时，答案都会随机排列。

---

有很多数组改组的例子 - 这是一个很好的例子(来自“Nate Cook”这里... How do I shuffle an array in Swift?):

extension MutableCollection where Indices.Iterator.Element == Index {
    /// Shuffles the contents of this collection.
    mutating func shuffle() {
        let c = count
        guard c > 1 else { return }

        for (firstUnshuffled , unshuffledCount) in zip(indices, stride(from: c, to: 1, by: -1)) {
            let d: IndexDistance = numericCast(arc4random_uniform(numericCast(unshuffledCount)))
            guard d != 0 else { continue }
            let i = index(firstUnshuffled, offsetBy: d)
            swap(&self[firstUnshuffled], &self[i])
        }
    }
}

extension Sequence {
    /// Returns an array with the contents of this sequence, shuffled.
    func shuffled() -> [Iterator.Element] {
        var result = Array(self)
        result.shuffle()
        return result
    }
}