Can't add user location button on an iOS 6 map - iphone

Question

I'm developing an application that uses an iOS 6 MKMap view and I would like to enable the "user location button" (the one that you see at the bottom-left of the screen when you are using the Maps application).
I didn't find anything that could help me so I've tried to make this button myself with this code:
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
CLLocationCoordinate2D currentCoordinates;
currentCoordinates.latitude = newLocation.coordinate.latitude;
currentCoordinates.longitude = newLocation.coordinate.longitude;
MKCoordinateRegion viewRegion = MKCoordinateRegionMake(currentCoordinates, _mapView.region.span);
[_mapView setRegion:viewRegion animated:YES];
[locationManager stopUpdatingLocation];
}
- (IBAction)moveToCurrentLocation:(id)sender {
[locationManager startUpdatingLocation];
}
So when I press the button the locationManager updates user's current location and the map changes it's region with a new one centered on user's current location and with the same span.
Now I have another problem: when I press the button the maps moves to the right coordinates but it also zooms out (in other words the span increases) even if I crete a new region with the old span.
I can't understand this behavior, I would like to preserve the old span as the Map app does.

Answer 1

That button on maps is toggling the userTrackingMode property on the mapView, so set it to one of these:
MKUserTrackingModeNone //nothing, normal map view
MKUserTrackingModeFollow //user is highlighted and stays centered on map when you move
MKUserTrackingModeFollowWithHeading //you get the heading as well, so your direction is up on the map

Answer 2

If you want to use the official iOS button for that, this code will add it to your UIToolbar and connect it to your mapview
UIBarButtonItem *trackingButton = [[MKUserTrackingBarButtonItem alloc] initWithMapView:self.mapView];
NSMutableArray *items = [[NSMutableArray alloc] initWithArray:self.toolbar.items];
[items addObject:trackingButton];
[self.toolbar setItems:items];