Question

Why will my code not remove the map annotation?

I hit the button and it gets the users location and then pins it to the map. The problem is that when the button is hit a second, third, ……. time It just keeps adding pins instead of removing the first pin (simulating replacing the pin).

I have tried adding another button (clear pins) and following this thread :http://stackoverflow.com/questions/3027392/how-to-delete-all-annotations-on-a-mkmapview but the app just crashes with no debug info.

But in theory my code should work. So what am I not understanding?

- (IBAction)getLocation:(id)sender {
    MapAnnotation *ann1 =[[[MapAnnotation alloc] init]autorelease]; 

    // remove annotation
    [mapView removeAnnotation:ann1];


    locationManager = [[CLLocationManager alloc] init];
    locationManager.distanceFilter=kCLDistanceFilterNone;
    locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;
    [locationManager startUpdatingLocation];

    [mapView setMapType:MKMapTypeStandard];
    [mapView setZoomEnabled:YES];
    [mapView setScrollEnabled:YES];
    MKCoordinateRegion region = {{0.0,0.0},{0.0,0.0}};
    region.center.latitude = locationManager.location.coordinate.latitude;
    region.center.longitude = locationManager.location.coordinate.longitude;
    region.span.longitudeDelta = 0.005f;
    region.span.latitudeDelta = 0.005f;
    [mapView setRegion:region animated:YES];
    [mapView setDelegate:sender];

    MKCoordinateRegion location1;
    location1.center.latitude =locationManager.location.coordinate.latitude;
    location1.center.longitude= locationManager.location.coordinate.longitude;
    location1.span.longitudeDelta=0.1;
    location1.span.latitudeDelta =0.1;


    // Add Annotation
    //MapAnnotation *ann1 =[[MapAnnotation alloc] init];
    ann1.title=@"You Parked Here";
    ann1.subtitle=@"";
    ann1.coordinate= location1.center;
    [mapView addAnnotation:ann1];

}

Answer 1

You’re removing an annotation that you just created, and which hasn’t been added to the map:

MapAnnotation *ann1 =[[[MapAnnotation alloc] init]autorelease];
// remove annotation
[mapView removeAnnotation:ann1];

You can either locate the annotation on the map, and then remove it, or you can take a heavy-handed approach and simply remove all the annotations in one swoop. Since I don’t know the UI interaction, I can’t really outline how to locate the annotation for you. However, here’s how to remove all:

NSMutableArray *annotations = [NSMutableArray array];
for (id annotation in [mapView annotations])
{
  [annotations addObject:annotation];
}
[mapView removeAnnotations:annotations];

HTH.