PreferencesViewController.swift

import UIKit

class PreferencesViewController: UIViewController {
  
  @IBOutlet var usernameLabel: UILabel!
  @IBOutlet var profilePic: UIImageView!
  @IBOutlet var profileBox: UIView!
  @IBOutlet var signOutButton: UIButton!
  @IBOutlet var learningLanguageTextField: UITextField!
  @IBOutlet var translationTextField: UITextField!
  
  var lastClickedTextField: UITextField?
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    createLocalePicker()
    createToolbarForLocalePicker()
  }
  
  func createLocalePicker() {
    
    let localePickerView = UIPickerView()
    localePickerView.delegate = self
    
    // add a one picker view to the both of locale text fields
    learningLanguageTextField.inputView = localePickerView
    translationTextField.inputView = localePickerView
  }
  
  func createToolbarForLocalePicker() {
    let toolBar = UIToolbar()
    toolBar.sizeToFit()
    
    let doneButton = UIBarButtonItem(title: "Done", style: .done, target: self, action: #selector(dismissKeyboard))
    
    toolBar.setItems([doneButton], animated: false)
    toolBar.isUserInteractionEnabled = true
    
    learningLanguageTextField.inputAccessoryView = toolBar
    translationTextField.inputAccessoryView = toolBar
  }
  
  
  @objc func dismissKeyboard() {
    view.endEditing(true)
  }
  
  // Make set your list as you wish.
  var localeList = Constants.LocaleList
  
  // This Action had been connected with both of UITextFields.
  @IBAction func textFieldBeginEditing(_ sender: UITextField) {
    // Update last clicked text field.
    lastClickedTextField = sender
    print("lastClickedTextField is updated.")
  }
}

extension PreferencesViewController: UIPickerViewDelegate, UIPickerViewDataSource{
  func numberOfComponents(in pickerView: UIPickerView) -> Int {
    return 1
  }
  
  func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
    return localeList.count
  }
  
  func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
    return localeList[row]
  }
    
  func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
    // upload selected item into the last clicked text field.
    lastClickedTextField?.text = localeList[row]
  }
  
  func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
    var label: UILabel
    
    if let view = view as? UILabel {
      label = view
    } else {
      label = UILabel()
    }
    label.textAlignment = .center
    label.text = localeList[row] 
    return label
  }
}