How to add annotations to MKMapView asynchronously?

Question

I have a lot of annotations to be added to a mkmapview. When i add the annotations, the app freezes for a short period of time. I have understand that the main thread is the only thread allowed to add UI to view, if this is true, how to i make this operation not freeze the app?

// in viewdidLoad
for (NSManagedObject *object in requestResults) {
     CustomAnnotation *customAnnotation = [[CustomAnnotation alloc] init];
     customAnnotation.title = object.title;
     customAnnotation.coordinate = CLLocationCoordinate2DMake([object.latitude doubleValue], [object.longitude doubleValue]);
     [_mapView addAnnotation:customAnnotation];
} 
} // end viewdidload

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id<MKAnnotation>)annotation
{
// shows the annotation with a custom image
    MKPinAnnotationView *customPinView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"mapAnnotation"];
    CustomAnnotation *customAnnotation = (id) annotation;
    customPinView.image = [UIImage imageNamed:@"green"];
    return customPinView;
}

Answer 1

You can use Grand Central Dispatch - GCD for doing this.

Try with:

- (void)viewDidLoad
{
  dispatch_async(dispatch_get_global_queue(0, 0), ^{
     for (NSManagedObject *object in requestResults)
     {
        CustomAnnotation *customAnnotation = [[CustomAnnotation alloc] init];
        customAnnotation.title = object.title;
        customAnnotation.coordinate = CLLocationCoordinate2DMake([object.latitude doubleValue], [object.longitude doubleValue]);
        dispatch_async(dispatch_get_main_queue(), ^{
           [_mapView addAnnotation:customAnnotation];
        });
     }
  });
}

This is a nice tutorial: GCD and threading