MapKit and Text Input - iOS Programming: The Big Nerd Ranch Guide - page 168

MKCoordinateRegionMakeWithDistance , allows you to specify a region with a
CLLocationCoordinate2D and the north-south and east-west limits of the zoom in
meters. For the limits, we'll use 250 by 250 meters. For the coordinate, we need the user's
location. Where can we get that?
How about the MKUserLocation object that the MKMapView sends its delegate in the
mapView:didUpdateUserLocation: message? Search the documentation for
MKUserLocation , and you'll find it has a property called location that holds the
current location of the device. Keep drilling down, and you'll find that location points
to a CLLocation object, which has a coordinate property of type CLLoca-
tionCoordinate2D . Success! We can use information in the MKUserLocation to
prepare an MKCoordinateRegion , which we then can use to set the region property
of the map view.
From what we know now, getting the information from the MKUserLocation takes two
steps: we would send MKUserLocation the message location and then send the re-
turned CLLocation object the message coordinate . The data returned from co-
ordinate then would become the MKCoordinateRegion 's center .
But nosing around the API Reference has its rewards. Before we add this code to
WhereamiViewController.m , take another look at the MKUserLocation refer-
ence. At the top, it tells us that MKUserLocation conforms to the protocol MKAn-
notation . Click on the link for that protocol, and you'll see that classes conforming to
it are required to have a property named coordinate of type CLLoca-
tionCoordinate2D . So we can simplify the process and send the message co-
ordinate directly to the MKUserLocation .
In WhereamiViewController.m , add the new code to
mapView:didUpdateUserLocation: .
- (void)mapView:(MKMapView *)mapView
didUpdateUserLocation:(MKUserLocation *)userLocation
{
CLLocationCoordinate2D loc = [userLocation coordinate];
MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(loc, 250, 250);
[worldView setRegion:region animated:YES];
}
Notice that the MKMapView is sent the message setRegion:animated: instead of
simply setRegion: . What's the difference? Check the documentation.