Question

In my viewcontroller I use Maps and I load a list of pins.
When I move the map or zoom in or out it, my app crashes and displays this error:

[GMMGeoTileImageData isEqualToString:]: unrecognized selector sent to instance 0x862d3b0

This is my code of the view controller:

    - (void)viewDidLoad
    {

        statoAnn = [[NSMutableString alloc] initWithFormat:@"false"];

        //bottone annulla per tornare indietro
        UIBarButtonItem *annullaButton = [[[UIBarButtonItem alloc] initWithTitle:@"Annulla" style:UIBarButtonItemStylePlain target:self action:@selector(backView)] autorelease];
        self.navigationItem.leftBarButtonItem = annullaButton;


        //inizializzo la mappa
        mapView = [[MKMapView alloc] initWithFrame:CGRectMake(0, 0, 320, 416)];
        mapView.delegate = self;
        mapView.mapType = MKMapTypeStandard;
        [self.view addSubview:mapView];

        [self setGmaps:arrData];

        [super viewDidLoad];
    }


/** inizializzo l'annotation del poi mappa **/
- (void) setGmaps:(NSMutableArray*)inputData { 

    // setto la lat e lng 
    CLLocationDegrees latitude;
    CLLocationDegrees longitude;
    CLLocationCoordinate2D poiLocation;
    arrAnn = [[NSMutableArray alloc] init];

    for(int i=0; i<[inputData count]; i++) {

        //ricavo la lat e lng del pin
        latitude  = [[[inputData objectAtIndex:i] objectForKey:@"latitude"]  doubleValue];
        longitude = [[[inputData objectAtIndex:i] objectForKey:@"longitude"] doubleValue];

        // setto la location del poi
        poiLocation.latitude = latitude;
        poiLocation.longitude = longitude;
        //[[[CLLocation alloc] initWithLatitude:latitude longitude:longitude] autorelease];

        //setto il pin
        Annotation *ann = [[Annotation alloc] initWithCoordinate:poiLocation];
        ann.title = [[inputData objectAtIndex:i] objectForKey:@"label"];
        [arrAnn addObject:ann];
        [ann release]; 

    }


    if (nil != self.arrAnn) {

        [self.mapView addAnnotations:arrAnn];
        //self.ann = nil;
        self.arrAnn = nil;
    }

}

/** setto il pin nella mappa ***/
- (void)setCurrentLocation:(CLLocation *)location {

    MKCoordinateRegion region = {{0.0f, 0.0f}, {0.0f, 0.0f}};

    region.center = location.coordinate;

    region.span.longitudeDelta = 0.1f;
    region.span.latitudeDelta  = 0.1f;

    [self.mapView setRegion:region animated:YES];
    [self.mapView regionThatFits:region];
}


- (MKAnnotationView *)mapView:(MKMapView *)mapViewTemp viewForAnnotation:(id <MKAnnotation>)annotation {

    MKPinAnnotationView *view = nil; // return nil for the current user location

        view = (MKPinAnnotationView *)[mapView dequeueReusableAnnotationViewWithIdentifier:@"identifier"];

        if (nil == view) {
            view = [[[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"identifier"] autorelease];
            view.rightCalloutAccessoryView = [UIButton buttonWithType:UIButtonTypeDetailDisclosure];
        }

        [view setPinColor:MKPinAnnotationColorPurple];
        [view setCanShowCallout:YES];
        [view setAnimatesDrop:YES];

    if (![statoAnn isEqualToString:@"true"]) {
        CLLocation *location = [[CLLocation alloc] initWithLatitude:annotation.coordinate.latitude
                                                          longitude:annotation.coordinate.longitude];
        [self setCurrentLocation:location];
        statoAnn = [NSMutableString stringWithFormat:@"true"];
    } 


    return view;
}

Answer 1

In viewForAnnotation, this line:

statoAnn = [NSMutableString stringWithFormat:@"true"];

sets statoAnn to an autoreleased string.

When the method exits, release is called on statoAnn and it no longer owns the memory it was pointing to. When the method is called again when you zoom or move the map, the memory that statoAnn was pointing to is now used by something else (GMMGeoTileImageData in this case). That object is not an NSString and doesn’t have an isEqualToString: method and you get the error you are seeing.

To fix this, set statoAnn so the value is retained like you are doing in viewDidLoad. For example, you could change it to:

statoAnn = [[NSMutableString alloc] initWithFormat:@"true"];

You could also declare statoAnn as a property (@property (nonatomic, copy) NSString *statoAnn) and just set it using self.statoAnn = @"true";. The property setter will do the retaining for you.

However, you don’t need to use a string to hold a “true” and “false” value. It’s much easier and efficient to use a plain BOOL and you won’t have to worry about retain/release since it’s a primitive type and not an object.

The other thing is that viewForAnnotation is not the right place to be setting the map view’s region in the first place. You can do that in viewDidLoad after the annotations are added.

Another thing: At the top of viewForAnnotation, you have the comment “return nil for the current user location” but that code doesn’t do that. It just initializes the view to nil. To actually do what the comment says, you need this:

MKPinAnnotationView *view = nil; 

// return nil for the current user location...
if ([annotation isKindOfClass:[MKUserLocation class]])
    return nil;

Finally, if the dequeueReusableAnnotationViewWithIdentifier does return a view (if view != nil), you need to set view.annotation to the current annotation since the re-used view may have been for a different annotation.