无法将类型“ [String]”的值分配给类型“ String？” （迅速）

Question

in swift (Xcode) for ios development, I'm trying to set my UILabel's text to the elements of an array. This is for a simple project where when you press a button: out of a array for 50 elements, the 50 elements will be randomized and then 3 will be chosen and i want those 3 to be displayed on the UILabel, but I get the error that I cannot assign value of type '[String]' to type 'String?' (Swift). Here is my code main code

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**)

I'm only a beginner at iOS developing

Code for the methods : //(choose) and (shuffle)

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

For your error: " unexpectedly found nil while unwrapping an Optional value ", have a look at my post about them, understanding '!' and '?' is crucial for Swift development: What are '!' and '?' marks used for in Swift

Also, as other answers mentioned also, you are returning an array value instead you should give a String value and then assign it to your label.text value. For this, you can try below:

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

Replace the above code with

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

Here you shuffle the array and put it in shuffled then pick array of first three elements in selectedThree .

selectedThree is an array of strings. We can either iterate the array to get the string or just use the first three elements.

Answer 3

I don't know where did you define shuffle and choose and I think you implemented them incorrectly.

I think you can just create a choose extension method that returns an array of strings:

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
}

And then you can just call it like this:

var chosenSongs = chooseFromArray(altSongs, amountToChoose: 3)

You said you want to display an array in a label. So I guess you want to do it like this?

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

I think that should fix it.