Should IBOutlets be strong or weak under ARC?

Question

I am developing exclusively for iOS 5 using ARC. Should IBOutlets to UIViews (and subclasses) be strong or weak?

The following:

@property (nonatomic, weak) IBOutlet UIButton *button;

Would get rid of all of this:

- (void)viewDidUnload
{
    // ...
    self.button = nil;
    // ...
}

Are there any problems doing this? The templates are using strong as are the automatically generated properties created when connecting directly to the header from the 'Interface Builder' editor, but why? The UIViewController already has a strong reference to its view which retains its subviews.

Answer 1

WARNING, OUTDATED ANSWER: this answer is not up to date as per WWDC 2015, for the correct answer refer to the accepted answer (Daniel Hall) above. This answer will stay for record.

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Summarized from the developer library:

From a practical perspective, in iOS and OS X outlets should be defined as declared properties. Outlets should generally be weak, except for those from File’s Owner to top-level objects in a nib file (or, in iOS, a storyboard scene) which should be strong. Outlets that you create will therefore typically be weak by default, because:

• Outlets that you create to, for example, subviews of a view controller’s view or a window controller’s window, are arbitrary references between objects that do not imply ownership.

• The strong outlets are frequently specified by framework classes (for example, UIViewController’s view outlet, or NSWindowController’s window outlet).

  @property (weak) IBOutlet MyView *viewContainerSubview;
  @property (strong) IBOutlet MyOtherClass *topLevelObject;