iOS - What is best way to manage memory for IBOutlets?

Question

I've been reviewing the Apple docs and sample code to try to determine the best way to manage memory for IBOutlets. I'm a little confused, to say the least.

The CurrentAddress sample code declares IBOutlets as properties:

@interface MapViewController : UIViewController <MKMapViewDelegate, MKReverseGeocoderDelegate>

{
    MKMapView *mapView;
    UIBarButtonItem *getAddressButton;
}
@property (nonatomic, retain) IBOutlet MKMapView *mapView;
@property (nonatomic, retain) IBOutlet UIBarButtonItem *getAddressButton;

Great. And these are released in dealloc:

- (void)dealloc
{
    [mapView release];
    [getAddressButton release];
    [super dealloc];
}

Now shouldn't these properties be set to assign? Because when set to retain, the IBOutlet's retain count will be increased twice: once when the nib is loaded and another time when the property is set? And wouldn't it be better to set these properties to nil instead of releasing in dealloc?

Answer 1

Apple docs says we should retain properties for iOS.
Retained outlets should be released and nil'ed in both dealloc and viewDidUnload.

On the Mac, every outlet which is not retained by a superview is automatically retained when loading the nib. That's not the case with iOS. That's why it's theoretically valid to only retain outlets other than views in the view hierarchy.

There's a very helpful post by Jeff LaMarche regarding this topic: Outlets, Cocoa vs. Cocoa Touch.

Answer 2

Once the nib loader finishes loading everything and connecting all the IBOutlets, it autoreleases all the objects it loaded. If your IBOutlet property was declared as assign, then the object it points to would be deleted next time the autorelease pool emptied.

You can set the properties to nil in dealloc instead of directly releasing them, the result is the same. The thing to watch for is, if you've provided your own implementation of the setter, you need to keep in mind that some of the other members of your object may already have been released.