限制用户缩放地图直到街道

Question

在我的应用程序中，要求用户不能缩放地图直到街道水平。我尝试了以下代码，但无法正常工作。通过此代码在某个缩放点，用户将无法放大或缩小。

func mapView(_ mapView: MKMapView,regionDidChangeAnimated animated: Bool){
    if self.mapView.currentZoomLevel > 16 {
        self.mapView.setCenterCoordinate(self.mapView.centerCoordinate, withZoomLevel: 16, animated: false)
    }
}


extension MKMapView {
open var currentZoomLevel: Int {
    let maxZoom: Double = 24
    let zoomScale = visibleMapRect.size.width / Double(frame.size.width)
    let zoomExponent = log2(zoomScale)
    return Int(maxZoom - ceil(zoomExponent))
}

open func setCenterCoordinate(_ centerCoordinate: CLLocationCoordinate2D,
                              withZoomLevel zoomLevel: Int,
                              animated: Bool) {
    let minZoomLevel = min(zoomLevel, 28)

    let span = coordinateSpan(centerCoordinate, andZoomLevel: minZoomLevel)
    let region = MKCoordinateRegion(center: centerCoordinate, span: span)

    setRegion(region, animated: animated)
}
}