Why is MKUserLocation in my annotations?

Question

I want to calculate distance between user and all annotations.
My annotations come from a csv file which is parsed. My annotations are in a Location class. Everything works fine except the distance calculation.

To calculate the distance, I found this code:

-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)newLocation
{

    for (Location *annotation in self.mapView.annotations) {
    CLLocationCoordinate2D coord = [annotation coordinate];
    CLLocationCoordinate2D userCoordinate = [[[self.mapView userLocation] location] coordinate];
    CLLocation *myLoc = [[CLLocation alloc] initWithLatitude:coord.latitude longitude:coord.longitude];
    CLLocation *userLoc = [[CLLocation alloc] initWithLatitude:userCoordinate.latitude longitude:userCoordinate.longitude];

     annotation.distance = [myLoc distanceFromLocation:userLoc];


        NSLog(@"Distance is = %f", annotation.distance);
} // ! CRASH !

NSArray *sortedArray;
sortedArray = [self.mapView.annotations sortedArrayUsingComparator:^NSComparisonResult(id a, id b) {
    NSNumber *first = [NSNumber numberWithDouble:[(Location*)a distance]];
    NSNumber *second = [NSNumber numberWithDouble:[(Location*)b distance]];
    return [first compare:second];
}];

But my app crash before the end of the loop. I discovered, with breakpoints, that there is a strange annotation (MKUserLocation* instead of Location*); After this MKUserLocation* one, the app crashes:

Not OK (crash):

OK (no crash):

Why is there MKUserLocation in my self.mapView.annotations? How to ignore it?

Log:

2014-09-22 06:01:47.965 MyFirstGPS2[472:60b] -[MKUserLocation setDistance:]: unrecognized selector sent to instance 0x9db0bb0
2014-09-22 06:01:48.030 MyFirstGPS2[472:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MKUserLocation setDistance:]: unrecognized selector sent to instance 0x9db0bb0'
*** First throw call stack:
(
    0   CoreFoundation                      0x01d971e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x01b168e5 objc_exception_throw + 44
    2   CoreFoundation                      0x01e34243 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
    3   CoreFoundation                      0x01d8750b ___forwarding___ + 1019
    4   CoreFoundation                      0x01d870ee _CF_forwarding_prep_0 + 14
    5   MyFirstGPS2                         0x00005043 -[HPViewController mapView:didUpdateUserLocation:] + 1203
    6   MapKit                              0x006825e6 -[MKMapView(MKHeadingAdditions) _stopTrackingHeading] + 469
    7   MapKit                              0x00666a92 -[MKMapView _setUserTrackingMode:animated:fromTrackingButton:] + 301
    8   MapKit                              0x00666960 -[MKMapView setUserTrackingMode:animated:] + 56
    9   MapKit                              0x00682176 -[MKMapView(MKHeadingAdditions) disableHeadingTracking:] + 65
    10  MapKit                              0x00669524 -[MKMapView _didChangeRegionMidstream:] + 672
    11  MapKit                              0x00671fbd -[MKMapView mapLayerDidChangeVisibleRegion:] + 66
    12  VectorKit                           0x0407a15e -[VKMapView mapDidChangeVisibleRegion:] + 78
    13  VectorKit                           0x040821fe -[VKMapCanvas cameraControllerDidChangeCameraState:] + 46
    14  VectorKit                           0x0409f1f7 -[VKMapCameraController updatePanWithTranslation:] + 231
    15  VectorKit                           0x0408268f -[VKMapCanvas updatePanWithTranslation:] + 63
    16  VectorKit                           0x0407aca9 -[VKMapView updatePanWithTranslation:] + 73
    17  MapKit                              0x0069e30b -[MKMapGestureController handlePan:] + 530
    18  UIKit                               0x00b724f4 _UIGestureRecognizerSendActions + 230
    19  UIKit                               0x00b71168 -[UIGestureRecognizer _updateGestureWithEvent:buttonEvent:] + 383
    20  UIKit                               0x00b72bdd -[UIGestureRecognizer _delayedUpdateGesture] + 60
    21  UIKit                               0x00b7613d ___UIGestureRecognizerUpdate_block_invoke + 57
    22  UIKit                               0x00b760be _UIGestureRecognizerRemoveObjectsFromArrayAndApplyBlocks + 317
    23  UIKit                               0x00b6c7ac _UIGestureRecognizerUpdate + 199
    24  UIKit                               0x00817a5a -[UIWindow _sendGesturesForEvent:] + 1291
    25  UIKit                               0x00818971 -[UIWindow sendEvent:] + 1021
    26  UIKit                               0x007ea5f2 -[UIApplication sendEvent:] + 242
    27  UIKit                               0x007d4353 _UIApplicationHandleEventQueue + 11455
    28  CoreFoundation                      0x01d2077f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
    29  CoreFoundation                      0x01d2010b __CFRunLoopDoSources0 + 235
    30  CoreFoundation                      0x01d3d1ae __CFRunLoopRun + 910
    31  CoreFoundation                      0x01d3c9d3 CFRunLoopRunSpecific + 467
    32  CoreFoundation                      0x01d3c7eb CFRunLoopRunInMode + 123
    33  GraphicsServices                    0x03acf5ee GSEventRunModal + 192
    34  GraphicsServices                    0x03acf42b GSEventRun + 104
    35  UIKit                               0x007d6f9b UIApplicationMain + 1225
    36  MyFirstGPS2                         0x00013592 main + 130
    37  libdyld.dylib                       0x0258a701 start + 1
    38  ???                                 0x00000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

Note: I'm using the code in this page to parse the csv file, I don't think that's the problem: http://blog.smartfrog.fr/post/32123941502/tutorial-ios-mapkit

Answer 1

The MKUserLocation is not a "strange" annotation.

It is the documented class of the user location (blue dot) annotation added by the map view when you set showsUserLocation to YES.

The map view's annotations array includes all annotations added to the map -- whether by you or by the map view (also note these will not be in any particular order).

To make sure you only process annotations of type Location, you can check the class of the annotation object before processing it using the isKindOfClass method.

If the annotation is not of that class, skip it (continue the loop).

You'll have a similar problem with the code that sorts the array since it will try to access the distance property on the MKUserLocation annotation.

Instead of trying to create a sorted array from the map view's annotations array, I suggest creating a separate array of just Location annotations in the for-loop (at the same time that you set distance) and then sort that array.

Example of using isKindOfClass in the for-loop and the sorting change:

-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)newLocation
{
    if (newLocation == nil) {
        //can happen if still waiting for user permission
        return;
    }
    if (!CLLocationCoordinate2DIsValid(newLocation.coordinate)) {
        //can happen if just resumed from some time in the background
        return;
    }

    //Declare and set user location variables outside the for-loop
    //since they won't be changing during the loop...
    CLLocationCoordinate2D userCoordinate = [[[self.mapView userLocation] location] coordinate];
    CLLocation *userLoc = [[CLLocation alloc] initWithLatitude:userCoordinate.latitude longitude:userCoordinate.longitude];

    //declare array in which you will put your Location annotations for sorting later...
    NSMutableArray *locAnnArray = [NSMutableArray array];

    //Declare the loop variable as a generic id<MKAnnotation>   
    for (id<MKAnnotation> annotation in self.mapView.annotations) {
        //Before processing the annotation, check it it's of type Location...
        if (! [annotation isKindOfClass:[Location class]]) {
            continue;
        }

        //Cast annotation to Location so we can see the distance property...
        Location *locAnn = (Location *)annotation;

        CLLocationCoordinate2D coord = [locAnn coordinate];
        CLLocation *myLoc = [[CLLocation alloc] initWithLatitude:coord.latitude longitude:coord.longitude];

        locAnn.distance = [myLoc distanceFromLocation:userLoc];

        NSLog(@"Distance is = %f", locAnn.distance);

        //Add Location annotation to local array for later sorting...   
        [locAnnArray addObject:locAnn];
    }

    //Sort our array of Location annotations...
    [locAnnArray sortUsingComparator:^NSComparisonResult(id a, id b) {
        NSNumber *first = [NSNumber numberWithDouble:[(Location*)a distance]];
        NSNumber *second = [NSNumber numberWithDouble:[(Location*)b distance]];
        return [first compare:second];
    }];

    //do something with the sorted array...
    //...
}