MKMapView: annotation's callout not shown when setting region - ios

Question

I show several custom annotation views on an MKMapView, and when user taps one of them, I change the region to be centered on it:
- (void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view
{
if ([view.annotation isKindOfClass:[CustomAnnotation class]]) {
double miles = 2.5;
double scalingFactor = ABS(cos(2 * M_PI * lat / 360.0));
MKCoordinateSpan span;
span.latitudeDelta = miles/69.0;
span.longitudeDelta = miles/(scalingFactor * 69.0);
MKCoordinateRegion region;
region.span = span;
region.center = self.coordinates;
[self.mapView setRegion:region animated:YES];
}
}
I see that, when the annotation already was shown, more or less, in the center of the map, the callout is displayed, but it is not when I tap an annotation closer to the map's border and the region has to "move more". I tried to select the annotation after the region setting animation ends:
- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated
{
for (id annotation in self.mapView.annotations) {
if ([annotation isKindOfClass:[CustomAnnotation class]]) {
if (((CustomAnnotation *)annotation).id == self.selectedAnnotation.id) {
[self.mapView selectAnnotation:annotation animated:YES];
}
}
}
}
But the callout is neither shown. If I don't change programmatically the region when tapping, all callouts are shown. How could I solve this?
Thanks