Soy muy nuevo en Swift y Xcode y he creado una aplicación simple de dos guiones gráficos que tiene una pantalla de bienvenida y un botón que activa una secuencia para el segundo guión gráfico (para el cual he creado su propia clase basada en UIVIewController). tiene un par de objetos UIPickerView ay un par de objetos UIDatePickerView y un botón. Tengo algunas acciones básicas bajo la función didSelectRow. Sin embargo, cuando construyo y ejecuto la aplicación, obtengo un comportamiento extraño y aparentemente aleatorio donde selecciono algo en el primer selector la vista me lleva de vuelta a la pantalla de bienvenida (¿una secuencia de desconexión?). ¡No he introducido ningún código para hacerlo! ¿Alguna idea?

import UIKit
class SecondViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource {
    @IBOutlet weak var cityPicker: UIPickerView!
    @IBOutlet weak var fromDatePicker: UIDatePicker!
    @IBOutlet weak var toDatePicker: UIDatePicker!
    @IBOutlet weak var nextThirdViewButton: UIButton!
    // temporay array for tsting - Populate with sqlite db extract
    var cityData = ["Please select city", "Beijing", "Calcutta", "Detroit", "Edinburgh", "Glasgow", "London", "Manchester", "New  York", "Rio de Janerio", "Washington"]
    // key variables and flags
    var cityPicked = false
    var fromTimePicked = false
    var toTimePicked = false
    var citySelected: String?
    var fromDate: Date?
    var toDate: Date?
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        fromDatePicker.minimumDate = Date()
        toDatePicker.minimumDate = Date()
        fromDate = Date()
        nextThirdViewButton.layer.cornerRadius = 15
        nextThirdViewButton.layer.masksToBounds = true
        cityPicker.delegate = self
        cityPicker.dataSource = self
    }
    //PickerView functions
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return cityData.count
    }
    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return cityData[row]
    }
    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        //check user has selcted a city from pickerview and set flags accordingly
        if self.cityData[row] != "Please select city" {
            self.citySelected = self.cityData[row]
            self.cityPicked = true
        } else {
            self.citySelected = "Please select city"
            self.cityPicked = false
        }
    }
    @IBAction func fromDatePicked(_ sender: Any) {
        fromDate = fromDatePicker.date
        if toTimePicked == true {
            checkDates(fromDate: fromDate!, toDate: toDate!)
        }
        fromTimePicked = true
    }
    @IBAction func toDatePicked(_ sender: Any) {
        toDate = toDatePicker.date
        checkDates(fromDate: fromDate!, toDate: toDate!)
    }
    //Function to check if 'to date' is earlier than 'from date' and issue alert
    func checkDates (fromDate: Date, toDate: Date) {
        switch toDate.compare(fromDate) {
        case .orderedDescending:
            toTimePicked = true
        case .orderedAscending:
            presentAlert(title: "Date Alert", message: "You can't travel back in time!")
            toTimePicked = false
        default: return
        }
    }
    // Function to move to third storyboard
    @IBAction func nextThirdViewButton(_ sender: Any) {
        if !(cityPicked && fromTimePicked && toTimePicked) {
            presentAlert(title: "You're not ready yet", message: "Please complete choices")
        } else {
            performSegue(withIdentifier: "thirdViewSeque", sender: nil)
        }
    }
    //reusable alert function
    func presentAlert(title: String, message: String) {
        let presentAlert = UIAlertController(title: title, message: message, preferredStyle: .alert)
        let dismissButton = UIAlertAction (title: "Dismiss", style: .cancel, handler: {
            (dateAlert: UIAlertAction) -> Void in
        })
        presentAlert.addAction(dismissButton)
        self.present(presentAlert, animated: true, completion: nil)
    }
}