iOS MapKit开发时，  往地图上添加自定义MKAnnotation图钉时， 经常会遇到图钉偏移的问题。

       // カスタムMKAnnotation作成
        func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
            guard annotation is MKPointAnnotation else { return nil }

            let identifier = "Annotation" + String(arc4random())
            var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: identifier)
            if annotationView == nil {
                annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: identifier)
                annotationView!.canShowCallout = true
                let btn = UIButton(type: .detailDisclosure)
                annotationView!.rightCalloutAccessoryView = btn
            } else {
                annotationView!.annotation = annotation
            

            let image = UIImage(named: annotationName)!.scaleImage(scaleSize: 0.8)
            // 重要通过设定annotationView的offset可以解决偏移的问题
            let offset = CGPoint(x: 0, y: -(image.size.height / 2))
            annotationView!.image = UIImage(named: annotationName)!.scaleImage(scaleSize: 0.8)
            annotationView!.centerOffset = offset
            annotationView!.displayPriority = .required
            
            formatAnnotation(pinView: annotationView!, forMapView: mapView)

            return annotationView
        }