geocoder對象是用網絡服務把經緯度坐標和用戶熟悉的地標相互轉換.地標是一個數據集合,包括街道,城市,州/省和國家等信息.
因為地geocoder是依賴于網絡.

用CLGeocoder來獲取地標信息

使用CLGeocoder來開始反向地理編碼的請求,創建這個類的實例并調用reverseGeocodeLocation:completionHandler:方法.這個對象會開始異步的反向地理編碼請求,并且把結果在completionHandler:里返回.

@implementation MyGeocoderViewController (CustomGeocodingAdditions)
- (void)geocodeLocation:(CLLocation*)location forAnnotation:(MapLocation*)annotation
{
    if (!geocoder)
        geocoder = [[CLGeocoder alloc] init];
 
    [geocoder reverseGeocodeLocation:location completionHandler:
        ^(NSArray* placemarks, NSError* error){
            if ([placemarks count] > 0)
            {
                annotation.placemark = [placemarks objectAtIndex:0];
 
                // Add a More Info button to the annotation's view.
                MKPinAnnotationView* view = (MKPinAnnotationView*)[map viewForAnnotation:annotation];
                if (view && (view.rightCalloutAccessoryView == nil))
                {
                    view.canShowCallout = YES;
                    view.rightCalloutAccessoryView = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
                }
            }
    }];
}
@end

將地名轉換成坐標

[geocoder geocodeAddressString:@"1 Infinite Loop"
     completionHandler:^(NSArray* placemarks, NSError* error){
         for (CLPlacemark* aPlacemark in placemarks)
         {
             // Process the placemark.
         }
}];