这几年似乎发生了一些变化，现在苹果建议一般使用strong。在他们的WWDC会议的证据是在会议407 -实现UI设计的界面生成器，并开始于32:30。我从他的话中摘录(如果不是完全引用的话，也几乎是引用了他的话):

Outlet连接通常应该是强的，特别是当我们连接的子视图或约束并不总是由 视图层次 在创建自定义视图时，可能需要弱出口连接，因为自定义视图引用了视图层次结构中的备份内容 一般来说不建议这样做

在其他方面，它应该总是强的只要我们的一些自定义视图没有与视图层次结构中的一些视图创建一个保留循环

编辑:

有些人可能会问这个问题。用强引用保存它是否不会创建一个保留循环作为根视图控制器而所属视图保留对它的引用?或者为什么会发生这种变化? 我想答案在这个演讲的前面，当他们描述如何从xib创建nib时。为VC和视图创建了一个单独的nib。我认为这可能是他们改变建议的原因。不过，如果能从苹果那里得到更深入的解释就好了。

出于性能考虑，IBOutlet应该是强大的。参见iOS 9中的故事板参考，Strong IBOutlet, Scene Dock

As explained in this paragraph, the outlets to subviews of the view controller’s view can be weak, because these subviews are already owned by the top-level object of the nib file. However, when an Outlet is defined as a weak pointer and the pointer is set, ARC calls the runtime function: id objc_storeWeak(id *object, id value); This adds the pointer (object) to a table using the object value as a key. This table is referred to as the weak table. ARC uses this table to store all the weak pointers of your application. Now, when the object value is deallocated, ARC will iterate over the weak table and set the weak reference to nil. Alternatively, ARC can call: void objc_destroyWeak(id * object) Then, the object is unregistered and objc_destroyWeak calls again: objc_storeWeak(id *object, nil) This book-keeping associated with a weak reference can take 2–3 times longer over the release of a strong reference. So, a weak reference introduces an overhead for the runtime that you can avoid by simply defining outlets as strong.

在Xcode 7中，它是强的

如果你观看了WWDC 2015会议407在界面生成器中实现UI设计，它建议(来自http://asciiwwdc.com/2015/sessions/407)

And the last option I want to point out is the storage type, which can either be strong or weak. In general you should make your outlet strong, especially if you are connecting an outlet to a sub view or to a constraint that's not always going to be retained by the view hierarchy. The only time you really need to make an outlet weak is if you have a custom view that references something back up the view hierarchy and in general that's not recommended. So I'm going to choose strong and I will click connect which will generate my outlet.

我认为最重要的信息是: xib中的元素自动位于view的子视图中。Subviews是NSArray。NSArray拥有它的元素。等等都有强指针。所以在大多数情况下你不需要创建另一个强指针(IBOutlet)

使用ARC，你不需要在viewDidUnload中做任何事情

目前苹果推荐的最佳实践是iboutlet是强的，除非特别需要弱的以避免保留循环。就像Johannes上面提到的，在2015年WWDC的“在界面生成器中实现UI设计”会议上，一位苹果工程师说:

我想指出的最后一个选项是存储类型，它可以 要么坚强，要么软弱。一般来说，你应该做出口 强，特别是当你连接一个输出到子视图或 约束并不总是会被视图保留 层次结构。唯一真正需要使outlet弱的时候是if 您有一个自定义视图，它引用视图中的备份内容 等级制度，一般来说不建议这样做。

我在Twitter上向IB团队的一位工程师询问了这个问题，他确认strong应该是默认的，并且开发人员文档正在更新。

https://twitter.com/_danielhall/status/620716996326350848 https://twitter.com/_danielhall/status/620717252216623104

警告，过时的答案:根据WWDC 2015，这个答案不是最新的，正确答案参考上面的公认答案(丹尼尔·霍尔)。这个答案将被记录下来。

从开发人员库总结:

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;

注意，IBOutletCollection应该是@property(强，非原子)。