Check whether zoom level changed

Question

I'm using MapKit on iPhone. How can I know when the user changes the zoom level (zoom in\out the map)?

I've tried to use mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated; but that's called even when the map is only dragged. Unfortunately, when the map is dragged the mapView.region.span changes as well...

Help?

10x

Answer 1

It is pretty simple to calculate the zoom level. See the snippet below. You can get the mRect parameter from the visibleMapRect property on your MKMapView instance.

+ (NSUInteger)zoomLevelForMapRect:(MKMapRect)mRect withMapViewSizeInPixels:(CGSize)viewSizeInPixels
{
    NSUInteger zoomLevel = MAXIMUM_ZOOM; // MAXIMUM_ZOOM is 20 with MapKit
    MKZoomScale zoomScale = mRect.size.width / viewSizeInPixels.width; //MKZoomScale is just a CGFloat typedef
    double zoomExponent = log2(zoomScale);
    zoomLevel = (NSUInteger)(MAXIMUM_ZOOM - ceil(zoomExponent));
    return zoomLevel;
}

You could probably just stop at the step for calculating the zoomScale as that will tell you if the zoom has changed at all.

I figured this stuff out from reading Troy Brants excellent blog posts on the topic:

http://troybrant.net/blog/2010/01/mkmapview-and-zoom-levels-a-visual-guide/

Swift 3

extension MKMapView {

    var zoomLevel: Int {
        let maxZoom: Double = 20
        let zoomScale = self.visibleMapRect.size.width / Double(self.frame.size.width)
        let zoomExponent = log2(zoomScale)
        return Int(maxZoom - ceil(zoomExponent))
    }

}