我已经在MKMapView中实现了Web Map Service，方法是将MKTileOverlay子类化并使用MKTileOverlayRenderer进行渲染。它可以正常工作并正确显示自定义地图。

当我调用mapView.addOverlay(polyLine)之类的方法来添加Polyline或Polygon时。 WMS叠加层被替换为Apple Maps。

// Set up the overlay and adds it to MKMapView.
func setupTileRenderer() {
    let wmsURL = formTemplate?.wmsURL
    let overlay = WMSTileOverlay(urlTemplate: wmsURL)
    overlay.canreplaceMapContent = true
    mapView.addOverlay(overlay,level: .aboveLabels)
    tileRenderer = MKTileOverlayRenderer(tileOverlay: overlay)
    wmsTileOverlay = overlay
}

func mapView(_ mapView: MKMapView,rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
    if overlay is MKPolyline {
        let render = MKPolylineRenderer(overlay: overlay)
        render.lineWidth = 2
        render.strokeColor = UIColor.red
        return render
    } else if overlay is MKPolygon {
        let render = MKPolygonRenderer(overlay: overlay)
        render.lineWidth = 2
        render.strokeColor = UIColor.red
        return render
    } else if overlay is WMSTileOverlay {
        return tileRenderer!
    }
    return MKOverlayRenderer(overlay: overlay)
}

如何防止这种情况？我不希望在添加折线或多边形时替换wmsTileOverlay。