地图视图上的倒圆叠加(MapKit、MKOverlay、Swift)

import MapKit

class CircleOverlay: NSObject, MKOverlay {
    var coordinate: CLLocationCoordinate2D
    var radius: CLLocationDistance
    
    init(coordinate: CLLocationCoordinate2D, radius: CLLocationDistance) {
        self.coordinate = coordinate
        self.radius = radius
    }
}

class CircleOverlayRenderer: MKOverlayRenderer {
    override func draw(_ mapRect: MKMapRect, zoomScale: MKZoomScale, in context: CGContext) {
        guard let circleOverlay = overlay as? CircleOverlay else {
            return
        }
        
        let circleRect = self.rect(for: circleOverlay.boundingMapRect)
        let circlePath = UIBezierPath(ovalIn: circleRect)
        
        context.setFillColor(UIColor.red.cgColor)
        context.addPath(circlePath.cgPath)
        context.fillPath()
    }
}

class ViewController: UIViewController, MKMapViewDelegate {
    @IBOutlet weak var mapView: MKMapView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 设置地图视图的代理
        mapView.delegate = self
        
        // 创建倒圆叠加层
        let coordinate = CLLocationCoordinate2D(latitude: 37.331705, longitude: -122.030237)
        let radius: CLLocationDistance = 1000
        let circleOverlay = CircleOverlay(coordinate: coordinate, radius: radius)
        
        // 添加叠加层到地图视图
        mapView.addOverlay(circleOverlay)
        
        // 设置地图视图的显示区域
        let region = MKCoordinateRegion(center: coordinate, latitudinalMeters: radius * 2, longitudinalMeters: radius * 2)
        mapView.setRegion(region, animated: true)
    }
    
    // 地图视图的代理方法，返回叠加层的渲染器
    func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
        if overlay is CircleOverlay {
            return CircleOverlayRenderer(overlay: overlay)
        }
        return MKOverlayRenderer(overlay: overlay)
    }
}