MKMapView的一个用于计算缩放比例的扩展

import Foundation
import MapKit

extension MKMapView {
    //缩放级别
    var zoomLevel: Double {
        //获取缩放级别
        get {
            return Double(log2(360 * (Double(self.frame.size.width/256)
                / self.region.span.longitudeDelta)) )
        }
        //设置缩放级别
        set (newZoomLevel){
            setCenterCoordinate(coordinate: self.centerCoordinate, zoomLevel: newZoomLevel,
                                animated: false)
        }
    }
    
    //根据区域范围、中心设置缩放比例
    public func setZoomLevel(geofenceCenter:CLLocationCoordinate2D,range:Double)  {
        
        let region = MKCoordinateRegionMakeWithDistance(geofenceCenter, range  ,range)
        let zoomLevel = Double(log2(360 * Double(self.frame.size.width/256)
            / region.span.longitudeDelta) )
        self.zoomLevel = zoomLevel
        
    }


    //设置缩放级别时调用
    private func setCenterCoordinate(coordinate: CLLocationCoordinate2D, zoomLevel: Double,
                                     animated: Bool){
        let span = MKCoordinateSpanMake(0,
                                        360 / pow(2, Double(zoomLevel)) * Double(self.frame.size.width) / 256)
        setRegion(MKCoordinateRegionMake(centerCoordinate, span), animated: animated)
    }
    
 
}