无法将类型“[String]”的值分配给类型“String？” （迅速）

Question

在用于 ios 开发的 swift (Xcode) 中，我正在尝试将 UILabel 的文本设置为数组的元素。这是一个简单的项目，当您按下按钮时：在 50 个元素的数组中，50 个元素将被随机化，然后选择 3 个，我希望这 3 个显示在 UILabel 上，但我得到了错误我无法将“[String]”类型的值分配给“String？” （迅速）。这是我的代码主要代码

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var altLabel: UILabel!
    @IBOutlet weak var asianLabel: UILabel!
    @IBOutlet weak var bluesLabel: UILabel!
    @IBOutlet weak var classicalLabel: UILabel!
    @IBOutlet weak var countryLabel: UILabel!
    @IBOutlet weak var danceLabel: UILabel!
    @IBOutlet weak var edmLabel: UILabel!
    @IBOutlet weak var emotionalLabel: UILabel!
    @IBOutlet weak var euroLabel: UILabel!
    @IBOutlet weak var indieLabel: UILabel!
    @IBOutlet weak var inspirationalLabel: UILabel!
    @IBOutlet weak var jazzLabel: UILabel!
    @IBOutlet weak var latinLabel: UILabel!
    @IBOutlet weak var newAgeLabel: UILabel!
    @IBOutlet weak var operaLabel: UILabel!
    @IBOutlet weak var popLabel: UILabel!
    @IBOutlet weak var rbLabel: UILabel!
    @IBOutlet weak var reggaeLabel: UILabel!
    @IBOutlet weak var rockLabel: UILabel!
    @IBOutlet weak var rapLabel: UILabel!

    override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    }

    override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
    }

    @IBAction func altButton(sender: UIButton) {

        let altSongs: [String] = ["Spirits by The Strumbellas", "Ride by Twenty One Pilots", "Ophelia by The Lumineers", "Dark Necessities by Red Hot Chili Peppers", "Bored to Death by Blink-182", "HandClap by Fitz And Tantrums", "Walking An A Dream by Empire Of The Sun", "Kiss This by The Struts", "Woman Woman by AWOLNATION", "First by Cold War Kids", "Way Down We Go by Kaleo", "Gone by Jr Jr", "Genghis Khan by Miike Snow", "Stressed Out by Twenty One Pilots", "Adventure Of A Lifetime by Coldplay", "2AM by Bear Hands", "Take It From Me by KONGOS", "Soundcheck by Catfish And The Bottlemen", "Brazil by Declan McKenna", "Destruction by Joywave", "Centuries by Fallout Boy", "Castle by Hasley", "First by Cold war Kids", "Unsteady (Erich Lee Gravity Remix) by X Ambadassadors", "Best Day Of My Life by American Authors", "Hymn For The Weekend by Coldplay", "Seven Nation Army by The White Stripes", "This is Gospel by Panic! At The Disco", "Riptide by Vance Joy", "Uma Thurman by Fallout Boy", "My Song Know What You Did In The Dark (Light Em Up) by Fall Out Boy", "Radioactive by Imagine Dragons", "Car Radio by Twenty One Pilots", "Walking On A Dream by Empire Of The Sun", "Viva La Vide by Coldplay", "Left Hand Free by Alt-J", "Tear in My Heart by Twenty One Pilots", "Death Of A Bachelor by Panic! At The Disco", "Demons by Imagine Dragons", "Emperor's New Clothes by Panic! At The Disco", "I Write Sins Not Tradegies by Panic! At The Disco", "Sail by AWOLNATION", "Twice by Catfish And The Bottlemen", "Colors by Hasley", "Nobody Really Cares If You Don't Go To The Party", "Courtney Barnett", "A Sky Full Of Stars", "On Top Of The World by Imagine Dragons", "Woman Woman by AWOLNATION", "Take Me T Church by Hozier"]

        var shuffled = altSongs.shuffle;
        shuffled = altSongs.choose(3)
        altLabel.text = shuffled  //(ending brackets are in place, just not shown here. **Rest of the code is just buttons structured in same format as this one**)

我只是 iOS 开发的初学者

方法代码：//（选择）和（随机播放）

import Foundation
import UIKit

extension Array {
    var shuffle: [Element] {
        var elements = self
        for index in indices.dropLast() {
            guard
            case let swapIndex = Int(arc4random_uniform(UInt32(count - index))) + index
                where swapIndex != index else {continue}
            swap(&elements[index], &elements[swapIndex])

        }
        return elements
    }
        mutating func shuffled() {
            for index in indices.dropLast() {
                guard
            case let swapIndex = Int(arc4random_uniform(UInt32(count - index))) + index
                where swapIndex != index
                    else { continue }
                swap(&self[index], &self[swapIndex])
            }
        }
        var chooseOne: Element {
            return self[Int(arc4random_uniform(UInt32(count)))]
        }
        func choose(n: Int) -> [Element] {
            return Array(shuffle.prefix(n))
        }
}

Answer 1

对于您的错误：“unexpectedly found nil while unwrapping an Optional value”，请查看我关于它们的帖子，了解“！”和 '？'对于 Swift 开发至关重要： What are '!' and '?' marks used for in Swift

此外，正如其他答案所提到的，您返回的是一个数组值，而不是您应该给出一个 String 值，然后将其分配给您的 label.text 值。为此，您可以尝试以下方法：

altLabel.text = "\(shuffled[0]), \(shuffled[1]), \(shuffled[2])"

Answer 2

var shuffled = altSongs.shuffle; // Line 1
shuffled = altSongs.choose(3)    // Line 2
altLabel.text = shuffled         // Line 3

将上面的代码替换为

let shuffled = altSongs.shuffle;
let selectedThree = shuffled.choose(3)
altLabel.text = selectedThree[0] + " " + selectedThree[1] + " " + selectedThree[2]

在这里，您将数组打乱并放入shuffled，然后在selectedThree 中选择前三个元素的数组。

selectedThree 是一个字符串数组。我们可以迭代数组以获取字符串，也可以只使用前三个元素。

Answer 3

我不知道你在哪里定义了shuffle 和choose，我认为你错误地实现了它们。

我认为您可以创建一个返回字符串数组的choose 扩展方法：

func chooseFromArray<T>(array: [T], amountToChoose: Int) -> [T] {
    var returnVal: [T] = []
    var arrayCopy = array
    for _ in 0..<amountToChoose {
        let chosen = Int(arc4random_uniform(UInt32(arrayCopy.count)))
        returnVal.append(arrayCopy[chosen])
        arrayCopy.removeAtIndex(chosen)
    }
    return returnVal
}

然后你可以这样称呼它：

var chosenSongs = chooseFromArray(altSongs, amountToChoose: 3)

你说你想在标签中显示一个数组。所以我猜你想这样做？

altLabel.text = chosenSongs.joinWithSeparator(", ")

我认为应该可以解决它。