Question

I’m developing an iOS 4 application using latest SDK and XCode 4.2.

I have enabled ARC on my project, and I’m trying to migrate a previous project to a new one that uses this feature (ARC).

The problem comes from an setter implementation. Here is my class (old version):

@interface RouteView : MKAnnotationView
{
    /**
     */
    MKMapView* _mapView;

    ...
}

@property (nonatomic, retain) MKMapView* mapView;

And its implementation:

@implementation RouteView

@synthesize mapView = _mapView;

-(void) setMapView:(MKMapView*) mapView
{
    [_mapView release];
    _mapView = [mapView retain];

    [self regionChanged];
}

I get two compiler errors in the two first line on setMapView: method.

How can I do a custom setter method with ARC enabled?

Answer 1

With ARC, you no longer need to release/retain objects, as it has automatic reference counting that puts retain and release calls in at compile time.

As a quick fix when merging an old program, you can comment out any lines that have:

• [myObject retain]
• [myObject release]

Just make sure that you don’t remove any functionality when you remove that part. In your application, you would need to replace [mapView retain] with mapView, as you still need to set the object, just without retaining it.

So your setMapView method would look something like this:

-(void) setMapView:(MKMapView*) mapView
{
    //[_mapView release];          //Don't need this line anymore.
    //_mapView = [mapView retain]; //Don't need this line either.

    _mapView = mapView //You still want to set the mapView, just not retain it.

    [self regionChanged];
}