Index out of bounds error for UIView animation method

Question

I am getting an index out of bounds error, but I can't figure out why. The code compiles fine, but the error appears at the following line (animation):

import UIKit

class MenuViewController: UIViewController {

    private let contentView = UIView()
    private let logoView = UIImageView()
    private let buttonView = UIView()
    private var gameButtons = [RoundedButton]()
    private let scoreView = UIView()
    private let titleLabel = UILabel()
    private let recentScoreLabel = UILabel()
    private let highscoreLabel = UILabel()

    private let titles = [
        "Multiple Choice",
        "Image Quiz",
        "Right or wrong",
        "Emoji Riddle"

    ]

    private var recentScores = [Int]()
    private var highscores = [Int]()
    private var scoreIndex = 0
    private var timer = Timer()

    private var midXConstraints: [NSLayoutConstraint]!
    private var leftConstraints: [NSLayoutConstraint]!
    private var rightConstraints: [NSLayoutConstraint]!

    override  func viewDidLoad() {
        super.viewDidLoad()
        navigationController?.navigationBar.barStyle = .blackTranslucent
        navigationController?.navigationBar.tintColor = UIColor.white
        view.backgroundColor = UIColor(red: 41/255, green: 128/255, blue: 185/255, alpha: 1.0)
        layoutView()
    }

    override func viewWillAppear(_ animated: Bool) {
        navigationController?.navigationBar.isHidden = true
    }

    func updateScores() {
        recentScores = [
            UserDefaults.standard.integer(forKey: multipleChoiceRecentscoreIdentifier),
            UserDefaults.standard.integer(forKey: imageQuizRecentscoreIdentifier),
            UserDefaults.standard.integer(forKey: rightWrongRecentscoreIdentifier),
            UserDefaults.standard.integer(forKey: emojiRecentscoreIdentifier)
        ]

        highscores = [
            UserDefaults.standard.integer(forKey: multipleChoiceHighScoreIdentifier),
            UserDefaults.standard.integer(forKey: imageQuizHighScoreIdentifier),
            UserDefaults.standard.integer(forKey: rightWrongHighscoreIdentifier),
            UserDefaults.standard.integer(forKey: emojiHighscoreIdentifier)
        ]
    }

    func layoutView() {
        contentView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(contentView)

        logoView.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(logoView)
        logoView.image = UIImage(named: "logo")

        buttonView.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(buttonView)

        for (index,title) in titles.enumerated() {
            let button = RoundedButton()
            button.translatesAutoresizingMaskIntoConstraints = false
            buttonView.addSubview(button)
            button.backgroundColor = UIColor(red: 52/255, green: 152/255, blue: 219/255, alpha: 1.0)
            button.titleLabel?.font = UIFont.boldSystemFont(ofSize: 20)
            button.setTitle(title, for: .normal)
            button.tag = index
            gameButtons.append(button)
        }

        scoreView.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(scoreView)

        titleLabel.translatesAutoresizingMaskIntoConstraints = false
        recentScoreLabel.translatesAutoresizingMaskIntoConstraints = false
        highscoreLabel.translatesAutoresizingMaskIntoConstraints = false
        scoreView.addSubview(titleLabel)
        scoreView.addSubview(recentScoreLabel)
        scoreView.addSubview(highscoreLabel)

        titleLabel.textAlignment = .center
        titleLabel.font = UIFont.boldSystemFont(ofSize: 30)
        titleLabel.textColor = UIColor.white
        recentScoreLabel.textColor = UIColor.white
        highscoreLabel.font = UIFont.boldSystemFont(ofSize: 20)
        highscoreLabel.textColor = UIColor.white

        titleLabel.text = titles[scoreIndex]
        recentScoreLabel.text = "Recent: " + String(UserDefaults.standard.integer(forKey: multipleChoiceRecentscoreIdentifier))
        highscoreLabel.text = "Highscore: " + String(UserDefaults.standard.integer(forKey: multipleChoiceHighScoreIdentifier))

        let constraints = [
            contentView.topAnchor.constraint(equalTo: topLayoutGuide.bottomAnchor, constant: 8.0),
            contentView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            contentView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            contentView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            logoView.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 20.0),
            logoView.widthAnchor.constraint(equalTo: contentView.widthAnchor, multiplier: 0.6),
            logoView.centerXAnchor.constraint(equalTo: contentView.centerXAnchor),
            logoView.heightAnchor.constraint(equalTo: contentView.heightAnchor, multiplier: 0.2),
            buttonView.topAnchor.constraint(equalTo: logoView.bottomAnchor, constant: 20.0),
            buttonView.bottomAnchor.constraint(equalTo: scoreView.topAnchor, constant: -20.0),
            buttonView.widthAnchor.constraint(equalTo: contentView.widthAnchor, multiplier: 0.6),
            buttonView.centerXAnchor.constraint(equalTo: contentView.centerXAnchor),
            gameButtons[0].topAnchor.constraint(equalTo: buttonView.topAnchor, constant: 8.0),
            gameButtons[0].bottomAnchor.constraint(equalTo: gameButtons[1].topAnchor, constant: -8.0),
            gameButtons[0].leadingAnchor.constraint(equalTo: buttonView.leadingAnchor),
            gameButtons[0].trailingAnchor.constraint(equalTo: buttonView.trailingAnchor),
            gameButtons[1].bottomAnchor.constraint(equalTo: gameButtons[2].topAnchor, constant: -8.0),
            gameButtons[1].leadingAnchor.constraint(equalTo: buttonView.leadingAnchor),
            gameButtons[1].trailingAnchor.constraint(equalTo: buttonView.trailingAnchor),
            gameButtons[2].bottomAnchor.constraint(equalTo: gameButtons[3].topAnchor, constant: -8.0),
            gameButtons[2].leadingAnchor.constraint(equalTo: buttonView.leadingAnchor),
            gameButtons[2].trailingAnchor.constraint(equalTo: buttonView.trailingAnchor),
            gameButtons[3].bottomAnchor.constraint(equalTo: buttonView.bottomAnchor, constant: -8.0),
            gameButtons[3].leadingAnchor.constraint(equalTo: buttonView.leadingAnchor),
            gameButtons[3].trailingAnchor.constraint(equalTo: buttonView.trailingAnchor),
            gameButtons[0].heightAnchor.constraint(equalTo: gameButtons[1].heightAnchor),
            gameButtons[1].heightAnchor.constraint(equalTo: gameButtons[2].heightAnchor),
            gameButtons[2].heightAnchor.constraint(equalTo: gameButtons[3].heightAnchor),
            scoreView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -40.0),
            scoreView.widthAnchor.constraint(equalTo: contentView.widthAnchor, multiplier: 0.6),
            scoreView.heightAnchor.constraint(equalTo: contentView.heightAnchor, multiplier: 0.3),
            titleLabel.topAnchor.constraint(equalTo: scoreView.topAnchor, constant: 8.0),
            titleLabel.leadingAnchor.constraint(equalTo: scoreView.leadingAnchor),
            titleLabel.trailingAnchor.constraint(equalTo: scoreView.trailingAnchor),
            titleLabel.bottomAnchor.constraint(equalTo: recentScoreLabel.topAnchor, constant: -8.0),
            recentScoreLabel.leadingAnchor.constraint(equalTo: scoreView.leadingAnchor),
            recentScoreLabel.trailingAnchor.constraint(equalTo: scoreView.trailingAnchor),
            recentScoreLabel.bottomAnchor.constraint(equalTo: highscoreLabel.topAnchor, constant: -8.0),
            highscoreLabel.leadingAnchor.constraint(equalTo: scoreView.leadingAnchor),
            highscoreLabel.trailingAnchor.constraint(equalTo: scoreView.trailingAnchor),
            highscoreLabel.bottomAnchor.constraint(equalTo: scoreView.bottomAnchor, constant: -8.0),
            titleLabel.heightAnchor.constraint(equalTo: recentScoreLabel.heightAnchor),
            recentScoreLabel.heightAnchor.constraint(equalTo: highscoreLabel.heightAnchor)
        ]

        midXConstraints = [scoreView.centerXAnchor.constraint(equalTo: contentView.centerXAnchor)]
        leftConstraints = [scoreView.trailingAnchor.constraint(equalTo: contentView.leadingAnchor)]
        rightConstraints = [scoreView.leadingAnchor.constraint(equalTo: contentView.trailingAnchor)]

        NSLayoutConstraint.activate(constraints)
        NSLayoutConstraint.activate(midXConstraints)

        timer = Timer.scheduledTimer(timeInterval: 3.0, target: self, selector: #selector(nextScores), userInfo: nil, repeats: true)
    }

    func nextScores() {
        scoreIndex = scoreIndex < (recentScores.count - 1) ? scoreIndex + 1 : 0
        UIView.animate(withDuration: 1.0, animations: {
            NSLayoutConstraint.deactivate(self.midXConstraints)
            NSLayoutConstraint.activate(self.leftConstraints)
            self.view.layoutIfNeeded()
        }) {(completion: Bool) in
            self.titleLabel.text = self.titles[self.scoreIndex]
            self.recentScoreLabel.text  = "Recent: " + String(self.recentScores[self.scoreIndex]) //Index out of bounds error appears here
            self.highscoreLabel.text = "Highscore: " + String(self.highscores[self.scoreIndex])
            NSLayoutConstraint.deactivate(self.leftConstraints)
            NSLayoutConstraint.activate(self.rightConstraints)
            self.view.layoutIfNeeded()
            UIView.animate(withDuration: 1.0, animations: {
                NSLayoutConstraint.deactivate(self.rightConstraints)
                NSLayoutConstraint.activate(self.midXConstraints)
                self.view.layoutIfNeeded()
            })
        }
    }



}

Answer 1

Please try this :

self.recentScores count is 0 and you are trying to access self.recentScores[0]

if self.recentScores.count > 0 {
    self.recentScoreLabel.text  = "Recent: " + String(self.recentScores[self.scoreIndex]) //Index out of bounds error appears here
}
if self.highscores.count > 0 {
    self.highscoreLabel.text = "Highscore: " + String(self.highscores[self.scoreIndex])
}

Answer 2

The recentScores is an empty array, i.e. it has 0 elements, and you are trying to access its first element. You don't append any element to this array. That's why you get "index out of bounds" error.