Drawing a polyline based on previous locations, to track a users path - ios

Question

I've used the following code in Xcode to display a poly line of my past locations. But it does not seem to appear. Any help will be appreciated.
Im not sure if my method to store the locations in an array is wrong or my code to display the poly line is wrong.
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation])
{
theLabel.text = "\(locations[0])"
storedLocations.append(locations[0] as CLLocation)
let location = locations[0]
let span:MKCoordinateSpan = MKCoordinateSpanMake(0.01, 0.01)
let myLocation:CLLocationCoordinate2D = CLLocationCoordinate2DMake(location.coordinate.latitude, location.coordinate.longitude)
let region:MKCoordinateRegion = MKCoordinateRegionMake(myLocation, span)
mapKitView.setRegion(region, animated:true)
print (location.speed)
print (location.altitude)
print (location.coordinate)
print (location.course) //Direction you are heading in NSEW
altitude.text = String(location.altitude)
mgrs.text = String(location.coordinate.latitude)
if (storedLocations.count > 1)
{
let sourceIndex = storedLocations.count - 1
let destinationIndex = storedLocations.count - 2
let c1 = storedLocations[sourceIndex].coordinate
let c2 = storedLocations[destinationIndex].coordinate
var a = [c1, c2]
let polyline = MKPolyline(coordinates: &a, count: a.count)
mapKitView.add(polyline)
print("running")
}
self.mapKitView.showsUserLocation = true
}
func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
let renderer = MKPolylineRenderer(overlay: overlay)
renderer.strokeColor = UIColor.blue
renderer.lineWidth = 5.0
return renderer
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}