Question

In my application I have a MKMapView where several annotations are shown. The map rotates based on the heading of the device. To rotate the map the following statement is performed (called by the method locationManager: didUpdateHeading:)

self.navigationMapView.mapView.transform = CGAffineTransformMakeRotation(-heading);

where the heading (magnetic) is expressed in radians. What I noticed it’s that even the annotations in the map rotate and I don’t want it. I tried to fix it in the following method:

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

    static NSString *identifier = @"AnnotationViewIdentifier";

    MKAnnotationView *av = [mapView dequeueReusableAnnotationViewWithIdentifier:identifier];

    if (av == nil) {
        av = [[[MKPinAnnotationView alloc]initWithAnnotation:annotation reuseIdentifier:identifier] autorelease];
    }
    else{
        av.annotation = annotation;
    }

    av.transform = CGAffineTransformMakeRotation(degreesToRadians(self.arController.currentHeading.magneticHeading)); 

    av.canShowCallout = YES;
    return av;

} 

and I want to call this method from “didUpdateHeading:” but I really don’t know how to do it. The TableView class has the reloadData function that calls the delegate method but here the things seem different. Any suggestions?!

Another question, my annotations on the map show the distance from the user, I would like to update them (distance label) as soon as the user change location. Any suggestions?!

Answer 1

So with a MKMapView having that be called properly is a little bit annoying. Essentially you have one of two options. Option 1: Create an array of the annotation on the screen and remove that from the map_view and then re-add them to the map_view. Essentially creating your own reload data function. Option 2: Do something simple such as

CGLocationCoordinate2D coordinate = map_view.center;
 map_view.center = coordinate;

— Essentially the point is to reset a property of the map causing it to redraw. However this option is not always going to work. Option 1 has a higher chance of working however that one can also fail, so if simply taking the annotations off and re-adding them causes nothing to happen then simply decreate the map and then recreate the map at the end of your map refresh function something like.

[my_map_view removeFromSuperView];
[my_map_view release];
my_map_view = nil;
my_map_view = [[MKMapView alloc] initWithFrame:CGRectMake(0,0,320,480)];

one of these options should work. I had to do option one for my solution however I know some people are lucky and option 2 works just as well.