如何在MapKit中绘制带有外框的覆盖图？

import MapKit

class CustomPolygon: MKPolygon {
    override func renderer(for overlay: MKOverlay) -> MKOverlayRenderer {
        if overlay is CustomPolygon {
            let renderer = CustomPolygonRenderer(overlay: overlay)
            return renderer
        }
        return MKOverlayRenderer(overlay: overlay)
    }
}

class CustomPolygonRenderer: MKPolygonRenderer {
    override func draw(_ mapRect: MKMapRect, zoomScale: MKZoomScale, in context: CGContext) {
        super.draw(mapRect, zoomScale: zoomScale, in: context)
        
        // 绘制外框
        let path = UIBezierPath(cgPath: self.path)
        path.lineWidth = 2.0
        UIColor.red.setStroke()
        path.stroke()
        
        // 填充内部区域
        UIColor.blue.withAlphaComponent(0.3).setFill()
        path.fill()
    }
}

// 在使用时，创建自定义的覆盖物对象，并将其添加到地图上
let polygon = CustomPolygon(coordinates: &coordinates, count: coordinates.count)
mapView.addOverlay(polygon)