iOS Mapkit Annotation is not getting draggable

I am new to iOS development and I need to implement a draggable annotation in iOS maps. my code is given below.whater ever I do I can't get a draggable annotation can anyone help with the annotations after that I need to get address of the location where the pin is pointing

RegistrationViewController.swift

class RegistrationViewController: UIViewController,UIPickerViewDelegate,UIPickerViewDataSource,MKMapViewDelegate{
    @IBOutlet weak var mapView: MKMapView!

    override func viewDidLoad() {
        super.viewDidLoad()
        var centerLocation = CLLocationCoordinate2DMake(12.964370125970357, 77.59643554937497)
        var mapspan = MKCoordinateSpanMake(0.01, 0.01)
        var mapregion = MKCoordinateRegionMake(centerLocation, mapspan)
        self.mapView.setRegion(mapregion, animated: true)

        let pin = pinAnnotation(title:"hello",subtitle:"how are you",coordinate:centerLocation)
        mapView.addAnnotation(pin)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    func mapView(mapView: MKMapView!, viewForAnnotation annotation: MKAnnotation!) -> MKAnnotationView! {
        if annotation is MKPointAnnotation {
            let pinAnnotationView = MKPinAnnotationView(annotation: annotation, reuseIdentifier: "myPin")
            pinAnnotationView.pinColor = .purple
            pinAnnotationView.isDraggable = true
            pinAnnotationView.canShowCallout = true
            pinAnnotationView.animatesDrop = true

            return pinAnnotationView
        }

        return nil
    }

    func mapView(_ mapView: MKMapView, annotationView view: MKAnnotationView, didChange newState: MKAnnotationViewDragState, fromOldState oldState: MKAnnotationViewDragState) {
        switch newState {
        case .starting:
            view.dragState = .dragging
        case .ending, .canceling:
            view.dragState = .none
        default: break
        }
    }

pinAnnotation.swift

import MapKit

class pinAnnotation:NSObject,MKAnnotation {
    var title:String?
    var subtitle: String?
    var coordinate: CLLocationCoordinate2D
    init(title:String,subtitle:String,coordinate:CLLocationCoordinate2D) {
        self.title = title
        self.subtitle = subtitle
        self.coordinate = coordinate
    }
}