为什么添加注释时地图视图会放大？

Question

I have a MKMapView that I configure with:

static let STARTING_MAP_RANGE: Double = 1000  // meters
. . .
let region: MKCoordinateRegion = MKCoordinateRegionMakeWithDistance(location,
                                                                    MapViewController.STARTING_MAP_RANGE,
                                                                    MapViewController.STARTING_MAP_RANGE)

mapView.setRegion(region, animated: true)

I add an annotation for the current location and it all looks fine. When I add an annotation for other points in the visible region, the MKMapView zooms in to the minimum area needed to show all the annotations.

The weird thing is that I tried to figure out where this was happening by printing out the bottom left and top right latitude and longitude like this:

private func printMapRegion(caller: String)
{
    let mapRect = mapView.visibleMapRect;
    let bottomLeft = MKCoordinateForMapPoint(MKMapPointMake(mapRect.origin.x, MKMapRectGetMaxY(mapRect)))
    let topRight = MKCoordinateForMapPoint(MKMapPointMake(MKMapRectGetMaxX(mapRect), mapRect.origin.y))

    print("\(caller):  (\(bottomLeft.latitude),\(bottomLeft.longitude)) -- (\(topRight.latitude),\(topRight.longitude))")
}

When I run this before and after setting the annotations, I get identical values, despite seeing the map zoom on the screen (both in the simulator and my iPhone).

I added a refresh button to reset the map. It works as far as zooming the map out, but it also reports that the bottom left and top right coordinates are the same before and after zooming.

Is there something wrong with my understanding of visibleMapRect?

Answer 1

I found that the reason for the zooming is that I was adding the annotations like this:

    mapView.removeAnnotations(mapView.annotations)
    mapView.addAnnotations(annotations)
    mapView.showAnnotations(mapView.annotations, animated: true)

Removing the call to showAnnotations eliminated the problem. I'm still curious as to why visibleMapRect is reporting the same bounding coordinates after the visible zoom.