title: How to calculate distance from user location to annotation when user moves
body: <p>I have an user location (blue dot) and annotations on <code>mapView</code>. When annotation is selected, I setting text to <code>distLabel</code> - "Distance to point %4.0f m.". How can I update that text label when user moves?</p>
  
  <p>didSelectAnnotationView:</p>
  
  <pre><code>- (void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view
  {
  
      CLLocation *pinLocation = 
        [[CLLocation alloc] initWithLatitude:
                          [(MyAnnotation*)[view annotation] coordinate].latitude 
                                   longitude:
                          [(MyAnnotation*)[view annotation] coordinate].longitude];
      CLLocation *userLocation = 
        [[CLLocation alloc] initWithLatitude:
                            self.mapView.userLocation.coordinate.latitude             
                                   longitude:
                                   self.mapView.userLocation.coordinate.longitude];        
      CLLocationDistance distance = [pinLocation distanceFromLocation:userLocation];
  
      [distLabel setText: [NSString stringWithFormat:@"Distance to point %4.0f m.",    
                                                       distance]];
  }
  </code></pre>
  
  <p>I know there is a function <code>didUpdateToLocation</code>, but how can I use it with <code>didSelectAnnotationView</code>?</p>
  
  <pre><code>- (void)locationManager:(CLLocationManager *)manager
      didUpdateToLocation:(CLLocation *)newLocation
             fromLocation:(CLLocation *)oldLocation
  {
    //Did update to location
  }
  </code></pre>