Geocode + MKPointAnnotation not playing nicely

Question

I'm having the weirdest issue, and it's doing my head in. A global variable which I've set up within a Singleton is reporting correctly from within the function it's set in, then as NULL from within the very next function (which is where I need to access it), but as correct from another View! So the variable is correctly set, but it's not behaving within a certain function. There is also a weird error warning being generated by the offending line (which I've marked between *).

The warning is:

Property access result unused - getters should not be used for side effects.

Apologies for the very spotty code. I'm prototyping and learning as I go, so it's a mishmash of things I've cobbled from the net. What the code does is recognise a long tap on a mapview, and then places a pin at the location (while recording the location), and I'm trying to use Geocode to show the address at the pin position.

The first function is as follows:

- (void)handleLongPress:(UIGestureRecognizer *)gestureRecognizer
{
if (gestureRecognizer.state != UIGestureRecognizerStateBegan)
    return;

CGPoint touchPoint = [gestureRecognizer locationInView:self.fullMapView];
CLLocationCoordinate2D touchMapCoordinate =
[self.fullMapView convertPoint:touchPoint toCoordinateFromView:self.fullMapView];

//save new birthplace in global variable        
globalsSingle.gblBirthplace = touchMapCoordinate;

//place user location and record it
MKUserLocation *location = fullMapView.userLocation;
globalsSingle.gblCurrentLocation = location.coordinate;

//first remove any previous birthplace pin
[self removeAllPinsButUserLocation];

[self reverseGeocode];

//place new birthplace pin
MKPointAnnotation *birthPlacePin = [[MKPointAnnotation alloc] init];
birthPlacePin.coordinate = touchMapCoordinate;
birthPlacePin.title = @"My Birthplace";
**** birthPlacePin.subtitle = @"%@", globalsSingle.gblAddress; ****
[self.fullMapView addAnnotation:birthPlacePin];

NSLog(@"gblAddress = %@", globalsSingle.gblAddress);

}

The above function calls the next:

-(void)reverseGeocode {

CLGeocoder *ceo = [[CLGeocoder alloc]init];
CLLocation *loc = [[CLLocation alloc]initWithLatitude:globalsSingle.gblBirthplace.latitude     longitude:globalsSingle.gblBirthplace.longitude]; //insert your coordinates

[ceo reverseGeocodeLocation: loc completionHandler:
 ^(NSArray *placemarks, NSError *error) {
     CLPlacemark *placemark = [placemarks objectAtIndex:0];
     //String to hold address
     NSString *locatedAt = [[placemark.addressDictionary  valueForKey:@"FormattedAddressLines"] componentsJoinedByString:@", "];

     // save the address text
     globalsSingle.gblAddress = locatedAt;

    NSLog(@"addressDictionary %@", placemark.addressDictionary);
    NSLog(@"placemark %@",placemark.region);
    NSLog(@"placemark %@",placemark.country);  // Give Country Name
    NSLog(@"placemark %@",placemark.locality); // Extract the city name
    NSLog(@"location %@",placemark.name);
    NSLog(@"location %@",placemark.ocean);
    NSLog(@"location %@",placemark.postalCode);
    NSLog(@"location %@",placemark.subLocality);
    NSLog(@"location %@",placemark.location);
   //Print the location to console
     NSLog(@"I am currently at %@",locatedAt);
     NSLog(@"gblAddress from reverse Geocode = %@", globalsSingle.gblAddress);

    }
 ];
}

What's even weirder (to me) is that the NSLog's from within reverseGeocode are all printing correctly, but the NSLog from the first function is reporting NULL, and is printing before the one from reverseGeocode even though it's (I assume) being executed second! For example, a debug output is:

2013-05-21 23:41:04.662 Project Name[5659:c07] gblAddress = (null)
2013-05-21 23:41:04.808 Project Name[5659:c07] gblAddress from reverse Geocode = Januária - MG, Brazil

Any help anyone could be bothered to offer I'd appreciate, as I'm bamboozled :)

Answer 1

When you are calling [self reverseGeocode]; the rest of handleLongPress will continue to run without waiting for reverseGeocode to finish. This is why you are seeing the print functions being called in an order you weren't expecting.

    [self performSelectorOnMainThread:@selector(reverseGeocode) withObject:nil waitUntilDone:YES];

If handleLongPress is running on the main thread, the above line can replace [self reverseGeocode] and should produce the expected results.

Answer 2

The method reverseGeocodeLocation:completionHandler: is executed asynchronously, which means that it will move on to the next lines before it finishes.

Asynchronous vs synchronous execution, what does it really mean?

It is called asynchronously because the method reverseGeocodeLocation:completionHandler: might need some time to do it, and when it is finished, the completion block is called.

You should place the new birthplace pin only after the completion block of the reverseGeocodeLocation is called, for example inside the completion block, to ensure you have got the placemark data first before placing the pin. Or you can just update the subtitle of the newly added pin inside the completion block.

[ceo reverseGeocodeLocation: loc completionHandler:
 ^(NSArray *placemarks, NSError *error) {
     CLPlacemark *placemark = [placemarks objectAtIndex:0];
     //String to hold address
     NSString *locatedAt = [[placemark.addressDictionary  valueForKey:@"FormattedAddressLines"] componentsJoinedByString:@", "];

     // save the address text
     globalsSingle.gblAddress = locatedAt;

     //place new birthplace pin
     MKPointAnnotation *birthPlacePin = [[MKPointAnnotation alloc] init];
     birthPlacePin.coordinate = globalsSingle.gblBirthplace;
     birthPlacePin.title = @"My Birthplace";
     birthPlacePin.subtitle = globalsSingle.gblAddress;
     [self.fullMapView addAnnotation:birthPlacePin];
    }
 ];
}