Overlaying a transparent PNG on top of the current location blue dot - ios

Question

i'm just playing around with Apple's CurrentAddress sample code and I was trying to use the trueHeading property to determine the direction the user is facing. While that proved simple enough, I wanted to display a transparent PNG on top of the current location dot and I wanted to rotate it in order to simulate a compass.
Here's the very basic code I've currently got:
#implementation MapViewController
#synthesize mapView, reverseGeocoder, getAddressButton;
- (void)viewDidLoad
{
[super viewDidLoad];
mapView.showsUserLocation = YES;
}
- (IBAction)reverseGeocodeCurrentLocation
{
self.reverseGeocoder =
[[[MKReverseGeocoder alloc] initWithCoordinate:mapView.userLocation.location.coordinate] autorelease];
reverseGeocoder.delegate = self;
[reverseGeocoder start];
}
- (void)reverseGeocoder:(MKReverseGeocoder *)geocoder didFailWithError:(NSError *)error
{
NSString *errorMessage = [error localizedDescription];
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Cannot obtain address."
message:errorMessage
cancelButtonTitle:#"OK"
otherButtonTitles:nil];
[alertView show];
[alertView release];
}
- (void)reverseGeocoder:(MKReverseGeocoder *)geocoder didFindPlacemark:(MKPlacemark *)placemark
{
PlacemarkViewController *placemarkViewController =
[[PlacemarkViewController alloc] initWithNibName:#"PlacemarkViewController" bundle:nil];
placemarkViewController.placemark = placemark;
[self presentModalViewController:placemarkViewController animated:YES];
}
- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{
// we have received our current location, so enable the "Get Current Address" button
[getAddressButton setEnabled:YES];
NSString *north = [NSString stringWithFormat:#"%f", self.mapView.userLocation.heading.trueHeading];
NSLog(#"here: %#", north);
}
#end
How can I overlay the PNG to the exact position of the blue dot and keep it there (following the dot if the user moves, that is)?

Answer 1

The point is that you need to implement mapView:viewForAnnotation: delegate method and look inside it for annotation objects which are not yours. Take a look at the code snipped:
- (MKAnnotationView *)mapView:(MKMapView *)map viewForAnnotation:(id <MKAnnotation>)annotation {
NSString static *defaultID = #"defaultID";
NSString static *userLocationID = #"userLocationID";
if ([annotation isKindOfClass:[MyAnnotation class]]) {
// your code here
} else {
MKAnnotationView *annotationView = [map dequeueReusableAnnotationViewWithIdentifier:userLocationID];
if (!annotationView) {
annotationView = [[[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:userLocationID] autorelease];
annotationView.image = [UIImage imageNamed:#"UserLocationIcon.png"];
}
return annotationView;
}
}