How to calculate distance from user location to annotation when user moves
The map view has a selectedAnnotations
property that you can use in the didUpdateToLocation
method to tell which annotation to get the distance from.
(By the way, if you are using the map view's userLocation
, you might want to use the map view's didUpdateUserLocation
delegate method instead of didUpdateToLocation
which is a CLLocationManager
delegate method.)
In the delegate method, you can check if there is any currently selected annotation and, if so, show the distance to that annotation (otherwise say "no annotation selected").
You might want to write a common method that can be called from both didSelectAnnotationView
and didUpdateUserLocation
to reduce code duplication.
For example:
-(void)updateDistanceToAnnotation:(id<MKAnnotation>)annotation
{
if (annotation == nil)
{
distLabel.text = @"No annotation selected";
return;
}
if (mapView.userLocation.location == nil)
{
distLabel.text = @"User location is unknown";
return;
}
CLLocation *pinLocation = [[CLLocation alloc]
initWithLatitude:annotation.coordinate.latitude
longitude:annotation.coordinate.longitude];
CLLocation *userLocation = [[CLLocation alloc]
initWithLatitude:mapView.userLocation.coordinate.latitude
longitude:mapView.userLocation.coordinate.longitude];
CLLocationDistance distance = [pinLocation distanceFromLocation:userLocation];
[distLabel setText: [NSString stringWithFormat:@"Distance to point %4.0f m.", distance]];
}
-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{
if (mapView.selectedAnnotations.count == 0)
//no annotation is currently selected
[self updateDistanceToAnnotation:nil];
else
//first object in array is currently selected annotation
[self updateDistanceToAnnotation:[mapView.selectedAnnotations objectAtIndex:0]];
}
- (void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view
{
[self updateDistanceToAnnotation:view.annotation];
}
Pavel Kaljunen
Updated on June 15, 2022Comments
-
Pavel Kaljunen almost 2 years
I have an user location (blue dot) and annotations on
mapView
. When annotation is selected, I setting text todistLabel
- "Distance to point %4.0f m.". How can I update that text label when user moves?didSelectAnnotationView:
- (void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view { CLLocation *pinLocation = [[CLLocation alloc] initWithLatitude: [(MyAnnotation*)[view annotation] coordinate].latitude longitude: [(MyAnnotation*)[view annotation] coordinate].longitude]; CLLocation *userLocation = [[CLLocation alloc] initWithLatitude: self.mapView.userLocation.coordinate.latitude longitude: self.mapView.userLocation.coordinate.longitude]; CLLocationDistance distance = [pinLocation distanceFromLocation:userLocation]; [distLabel setText: [NSString stringWithFormat:@"Distance to point %4.0f m.", distance]]; }
I know there is a function
didUpdateToLocation
, but how can I use it withdidSelectAnnotationView
?- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation { //Did update to location }
-
Pavel Kaljunen almost 12 yearsGreat answer as always from you! Thank you!