When to link annotation property in viewForAnnotation method

Question

I came across this piece of code in Apple's Location and Maps Programming Guide:

- (MKAnnotationView *)mapView:(MKMapView *)mapView
                      viewForAnnotation:(id <MKAnnotation>)annotation
{
    // If the annotation is the user location, just return nil.
    if ([annotation isKindOfClass:[MKUserLocation class]])
        return nil;

    // Handle any custom annotations.
    if ([annotation isKindOfClass:[MyCustomAnnotation class]])
    {
        // Try to dequeue an existing pin view first.
        MKPinAnnotationView*    pinView = (MKPinAnnotationView*)[mapView
        dequeueReusableAnnotationViewWithIdentifier:@"CustomPinAnnotationView"];

        if (!pinView)
        {
            // If an existing pin view was not available, create one.
            pinView = [[MKPinAnnotationView alloc] initWithAnnotation:annotation
                       reuseIdentifier:@"CustomPinAnnotationView"];
            pinView.pinColor = MKPinAnnotationColorRed;
            pinView.animatesDrop = YES;
            pinView.canShowCallout = YES;

            // If appropriate, customize the callout by adding accessory views (code not shown).
        }
        else
            pinView.annotation = annotation;

        return pinView;
    }

    return nil;
}

I have a question regarding this part:

else
    pinView.annotation = annotation;

I saw the same code in a Stackoverflow answer:

Unrelated, but you also need to set the view's annotation property when it is being re-used (in the case when it is not nil after the dequeue). So add an else block to the if (pinAnnotation == nil):

else {
    //annotation view being re-used, set annotation to current...
    pinAnnotation.annotation = annotation;
}

Why is the annotation property set in the else block? Shouldn't the annotation be set regardless if a view was reused or not?

Answer 1

You initialise the MKPinAnnotationView with the annotation so the else is just so you won't set it twice. It is perfectly fine to set it twice but of course inefficient.