Programming iOS 6, 3rd Edition

Geocoding

The term geocoding refers to the translation of an address to a coordinate and vice versa. Geocoding functionality is encapsulated in the CLGeocoder class; to use it, you’ll need to link to CoreLocation.framework. Geocoding takes time and might not succeed at all, as it depends upon network and server availability; moreover, results may be more or less uncertain. Therefore, all geocoding methods take a completion handler which will eventually be called with two arguments:

NSArray* placemark

An NSArray of CLPlacemark objects. If things went really well, the array will contain exactly one CLPlacemark; if there are multiple placemark objects, the first one is the best guess. If nil, something went wrong.

NSError* error

If the placemark array was nil, this argument reports the reason things went wrong.

A CLPlacemark can be used to initialize an MKPlacemark, a CLPlacemark subclass that adopts the MKAnnotation protocol, and is therefore suitable to be handed directly over to an MKMapView for display. Here is an (unbelievably simple-minded) example that allows the user to enter an address in a UISearchBar (Chapter 25) to be displayed in an MKMapView:

-(void)searchBarSearchButtonClicked:(UISearchBar *)searchBar { NSString* s = searchBar.text; [searchBar resignFirstResponder]; CLGeocoder* geo = [CLGeocoder new]; [geo geocodeAddressString:s completionHandler:^(NSArray *placemarks, NSError *error) { if (nil == placemarks) { NSLog(@"%@", error.localizedDescription); return; } CLPlacemark* ...