Should IBOutlets be strong or weak under ARC?

被采用的答案

答案仅是摘自官方文档的一个片段：

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;

大意是说，在 ARC 中,一般IBOutlet属性都推荐使用 weak,应该使用 strong 的 IBOutlet 是 File’s Owner连接到 nib 的顶层对象。
什么是 File’s Owner连接到 nib 的顶层对象呢？说白话一点，就是自定义的view，不是直接作为main view里面一个sub view直接显示出来，而是需要通过实例化创建出来的。你自己实例化，当然需要strong了，不然谁还替你保留对象所有权呢？

举例来说，UIViewController的view属性是strong，因为controller要直接拥有view。而添加到view上的subviews，作为IBOutlet只需要设置为weak就可以了，因为他们不是controller直接拥有的。直接拥有subviews的是controller的view，ARC会帮助管理内存。