using CLLocation objects as keys in dictionary

Question

Is it possible to use CLLocation objects as keys in a dictionary? When I try this, the [dictionary objectForKey: clLocationObj] always returns nil even when there are CLLocation keys already inserted with exactly the same latitude and longitude. What could I be doing wrong?

       for (Location *location in someArray) {
               CLLocation *locationKey = [[CLLocation alloc] initWithLatitude:[location.latitude doubleValue] longitude:[location.longtitude doubleValue]];
               LocationAnnotation *annotationAtLocation = [self.uniqueLocations objectForKey:locationKey];
               if (annotationAtLocation == nil)
                    NSLog(@"this is always nil");
       }

I know from my debugging that there are multiple objects of Location with the same latitude and longitude in someArray.

Answer 1

CLLocation does not seem to override isEqual to perform actual content comparison, instead it compares the equality based on object identity. Therefore it is not wise to use it as a key in a dictionary, unless you are always accessing it using the exact same object.

The solution you have described in a comment is quite good workaround for many situations:

I ended up converting the CLLocationCoordinate2D object into an NSValue and used that as the key to the dictionary.

Answer 2

There is NSValueMapKitGeometryExtensions category on NSValue in MapKit framework

//to set
NSValue *locationValue = [NSValue valueWithMKCoordinate:location.coordinate];
[dictionary setObject:object forKey:locationValue];

//to get
NSValue *coordinateValue = dictionary[locationValue];
CLLocationCoordinate2D coordinate = [coordinateValue MKCoordinateValue];