IBOutlets强或弱 - 它是否真的对内存管理产生影响？ （弧）

Question

I've been reading a lot recently on here and other sites about whether IBOutlets should be strong or weak. The official verdict is that they should be weak, except for when they reference top level xib objects.

This is fine.

However what I don't yet have a clear understanding of is why setting them to strong or weak actually would make a difference in terms of the app's memory management. In particular it seems since iOS6, viewDidUnload is not called on receiving a memory warning anymore, so in this sense the choice of weak or strong for IBOutlets would make no difference.

Am I right in thinking though that for view controllers no longer on the navigation stack (ie after they have been loaded then popped), that any IBOutlets declared as weak would then be released ?

Thanks for any insights !

Answer 1

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).

more

Answer 2

IBOutlets can declared weak because they will be created during XIB parsing and added to the UIView stack...so you don't need a strong reference to the object.

When you declare an IBOutlet weak you ensure that when the main UIView of UIViewcontroller disappear every subview will be deleted without any memory leak.