Gold Challenge: Dropping Pins (simple way)

import UIKit
import MapKit
// Gold Challenge
class MapViewController: UIViewController, MKMapViewDelegate {

// MARK: - Property

var mapView: MKMapView!

var index: Int!                                                                       // my add for the Gold Challenge

var coordinate1, coordinate2, coordinate3: CLLocationCoordinate2D!                    // my add for the Gold Challenge

var string1 = "Alghero"                                                               // my add for the Gold Challenge
var string1s = "The town where I was born"                                            // my add for the Gold Challenge
var string2 = "M√ľnchen"                                                               // my add for the Gold Challenge
var string2s = "The town where I live now"                                            // my add for the Gold Challenge
var string3 = "Moraine Lake"                                                          // my add for the Gold Challenge
var string3s = "The place where I would like to live"                                 // my add for the Gold Challenge

// MARK: - UIViewController Method

override func loadView() {
    mapView = MKMapView()
    view = mapView
    mapView.delegate = self                                                           // my add for the Gold Challenge
    
    coordinate1 = CLLocationCoordinate2D(latitude: 40.579693, longitude: 8.318887)    // my add for the Gold Challenge
    coordinate2 = CLLocationCoordinate2D(latitude: 48.1367, longitude: 11.58862)      // my add for the Gold Challenge
    coordinate3 = CLLocationCoordinate2D(latitude: 51.327847, longitude: -116.182474) // my add for the Gold Challenge
    
    let segmentedControl = UISegmentedControl(items: ["Standard", "Hybrid", "Satellite"])
    segmentedControl.backgroundColor = UIColor.white.withAlphaComponent(0.5)
    segmentedControl.selectedSegmentIndex = 0
    
    segmentedControl.addTarget(self, action: #selector(MapViewController.mapTypeChanged(_:)), for: .valueChanged)
    
    segmentedControl.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(segmentedControl)
    
    let topConstraint = segmentedControl.topAnchor.constraint(equalTo: topLayoutGuide.bottomAnchor, constant: 8)
    let margins = view.layoutMarginsGuide
    let leadingConstraint = segmentedControl.leadingAnchor.constraint(equalTo: margins.leadingAnchor)
    let trailingConstraint = segmentedControl.trailingAnchor.constraint(equalTo: margins.trailingAnchor)

    topConstraint.isActive = true
    leadingConstraint.isActive = true
    trailingConstraint.isActive = true
    
    /* ---------------------- my add for the Gold Challenge: create a button programmatically --------------------- */
    
    let button   = UIButton(type: UIButtonType.system)
    button.backgroundColor = UIColor.white.withAlphaComponent(0.0)
    button.setTitle("Pin Location", for: .normal)
    button.setTitleColor(UIColor.blue, for: .normal)
    button.layer.cornerRadius = 5
    
    button.addTarget(self, action: #selector(MapViewController.buttonAction(sender:)), for: .touchUpInside)
    
    button.translatesAutoresizingMaskIntoConstraints = false
    
    view.addSubview(button)
    
    let bottomConstraintBtn = button.bottomAnchor.constraint(equalTo: bottomLayoutGuide.topAnchor, constant: -10)
    let marginsBtn = view.layoutMarginsGuide
    let leadingConstraintBtn = button.leadingAnchor.constraint(equalTo: marginsBtn.leadingAnchor)
    let trailingConstraintBtn = button.trailingAnchor.constraint(equalTo: marginsBtn.trailingAnchor)
    
    bottomConstraintBtn.isActive = true
    leadingConstraintBtn.isActive = true
    trailingConstraintBtn.isActive = true
    
    /* ------------------------------------------------------------------------------------------------------------ */
}

override func viewDidLoad() {
    super.viewDidLoad()
    print("MapViewController loaded its view.")
}

// MARK: - Helper Methods

func mapTypeChanged(_ segControl: UISegmentedControl) {
    switch segControl.selectedSegmentIndex {
    case 0:
        mapView.mapType = .standard
    case 1:
        mapView.mapType = .hybrid
    case 2:
        mapView.mapType = .satellite
    default:
        break }
}

// my add for the Gold Challenge
func buttonAction(sender: UIButton!) {
    switch index {
    case nil, 2:
        index = 0
        point(title: string1, subTitle: string1s, coordinate: coordinate1)
    case 0:
        index = 1
        point(title: string2, subTitle: string2s, coordinate: coordinate2)
    case 1:
        index = 2
        point(title: string3, subTitle: string3s, coordinate: coordinate3)
    default:
        break
    }
}

// my add for the Gold Challenge
private func point(title: String!, subTitle: String!, coordinate: CLLocationCoordinate2D) {
    let region = MKCoordinateRegionMakeWithDistance(coordinate, 700, 700)
    mapView.setRegion(region, animated: true)
    
    let point = MKPointAnnotation()
    point.coordinate = coordinate
    point.title = title
    point.subtitle = subTitle
    mapView.addAnnotation(point)
}

// MARK: - MKMapViewDelegate Method

// my add for the Gold Challenge
func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView?  {
    var pinView = mapView.dequeueReusableAnnotationView(withIdentifier: "Test") as? MKPinAnnotationView
    if pinView == nil {
        pinView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: "Test")
        pinView!.canShowCallout = true
        pinView!.animatesDrop = true
        pinView!.pinTintColor = MKPinAnnotationView.purplePinColor()   // or: "pinView!.pinTintColor = UIColor.purple"
    }
    else {
        pinView!.annotation = annotation
    }
    return pinView                                                                                       // return nil
}

}