You might have noticed that when you insert an IBOutlet directly from Interface Builder you can select whether to have it as a weak or strong property. After a little search in the Apple developer’s library I have found when you should use one or the other:
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 should therefore typically be weak, because:
- Outlets that you create to subviews of a view controller’s view or a window controller’s window, for example, 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).
You can read more about it here.