在导航控制器上推送的viewController中实现MapKit的有效方法？

Question

I am trying to add a mapKit in a viewController in IB that I am pushing on top of my navigation controller but no matter where in the cycle I add the annotations it seems like the whole thing causes a delay and until mapKit is not rendered the scrollview that contains everything doesn't scroll easily. Is there a way to do this in iOS similar to Android in the background threads for instance?

Below is the code even without adding any annotation, rendering is still causing the delay. I'm pretty sure there's another way. Any idea?

class DetailViewController: UIViewController , MKMapViewDelegate{

    override func viewDidLoad() {
            super.viewDidLoad()
            self.mapView?.delegate = self
    }


      //changing the annotation
        func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
            if (annotation is MKUserLocation) {
                return nil
            }
            let reuseId = "detailMrker"
            var anView = mapView.dequeueReusableAnnotationView(withIdentifier: reuseId)
            if anView == nil {
                anView = MKAnnotationView(annotation: annotation, reuseIdentifier: reuseId)
                anView?.image = UIImage(named:"location.png")
                anView?.canShowCallout = true
            }
            else {
                anView?.annotation = annotation
            }
            return anView
        }

}

Answer 1

You CAN render a VC ahead of time, and present it from offscreen, with a modal presentation. If you absolutely must push from your UINavigationController, then you're stuck waiting for the VC to call the draw methods of its view, after the VC is pushed.

There are other things you can do ahead of time, however. Use something other than DetailFeedViewController as your CLLocationManagerDelegate, and MKMapDelegate. If you do so, you can get the user's location, set the map coordinates, and add you annotation, before the VC is pushed.