MKCoordinateregion's center changes when span changed - iphone

I have a MKCoordinateregion called region. I want to change span of this region without changing it's center. I am using following method to change zoom.

 -(void) changeZoom
    {

     NSLog(@"before zoom span, center are   %f, %f,%f,%f", region.span.latitudeDelta, region.span.longitudeDelta, mymap.centerCoordinate.latitude, mymap.centerCoordinate.longitude);
                region.span.latitudeDelta = current_factor ;
                region.span.longitudeDelta = current_factor ;
                region.center.latitude = mymap.centerCoordinate.latitude ;
                region.center.longitude = mymap.centerCoordinate.longitude ;
                [mymap setRegion:region animated:TRUE];

                NSLog(@"after zoom span, center are   %f, %f,%f,%f", region.span.latitudeDelta, region.span.longitudeDelta, mymap.c开发者_开发问答enterCoordinate.latitude, mymap.centerCoordinate.longitude);
    }

Log shows :

before zoom span, center are   0.021950, 0.021950,19.068080,72.838111
 after zoom span, center are   0.043901, 0.043901,19.068040,72.838154

This method set's span accurately as desired.But I dont want any change in the center's coordinate, Because when I zoom out and then zoom back I end up at a location different from starting location.

Is there any method so that zoom in and out are possible without any change in center?

Thanks for any help in advance.

---

Your before and after center coordinates are almost exactly the same, so it shouldn't be a problem. If you really want the exact same center coordinates, call setCenterCoordinate:animated: right after you use setRegion:animated: and pass some saved center coordinates.

CLLocationCoordinate2D originalCenter = mymap.centerCoordinate;
// ... adjust region
[mymap setCenterCoordinate:originalCenter animated:NO];

Also, you should use YES instead of TRUE for booleans:

[mymap setRegion:region animated:YES];

---

You need to adjust the region of the map to make sure the aspect ratio fits the frame size of the map view.

Once the region with the desired center is calculated, adjust the region as,

MKCoordinateRegion adjustedRegion = [mymap regionThatFits:region];
[mymap setRegion:adjustedRegion animated:TRUE];

See docs.