MKAnnotation 图像与自定义引脚图像的偏移

在iOS开发中，我们经常需要在地图上标记特定的位置。使用MKAnnotation可以轻松实现这个功能。MKAnnotation是一个协议，用于定义地图上的标注点。通过实现MKAnnotation协议，我们可以自定义标注点的样式、标题和副标题等信息。

swift
import MapKit
class CustomAnnotation: NSObject, MKAnnotation {
    var coordinate: CLLocationCoordinate2D
    var title: String?
    var subtitle: String?
    var image: UIImage?
    var centerOffset: CGPoint
    
    init(coordinate: CLLocationCoordinate2D, title: String?, subtitle: String?, image: UIImage?, centerOffset: CGPoint) {
        self.coordinate = coordinate
        self.title = title
        self.subtitle = subtitle
        self.image = image
        self.centerOffset = centerOffset
    }
}
class ViewController: UIViewController, MKMapViewDelegate {
    @IBOutlet weak var mapView: MKMapView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        mapView.delegate = self
        
        let coordinate = CLLocationCoordinate2D(latitude: 37.331705, longitude: -122.030237)
        let annotation = CustomAnnotation(coordinate: coordinate, title: "Apple Park", subtitle: "Cupertino, CA", image: UIImage(named: "custom_pin"), centerOffset: CGPoint(x: 0, y: -20))
        
        mapView.addAnnotation(annotation)
    }
    
    func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
        if annotation is CustomAnnotation {
            let reuseIdentifier = "CustomAnnotation"
            var annotationView = mapView.dequeueReusableAnnotationView(withIdentifier: reuseIdentifier)
            
            if annotationView == nil {
                annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: reuseIdentifier)
            } else {
                annotationView?.annotation = annotation
            }
            
            if let customAnnotation = annotation as? CustomAnnotation {
                annotationView?.image = customAnnotation.image
                annotationView?.centerOffset = customAnnotation.centerOffset
            }
            
            return annotationView
        }
        
        return nil
    }
}