unsafe_unretain和弱，并在ARC下分配? [英] unsafe_unretained and weak and assign under ARC?

问题描述

可能重复:
强/弱/保留/unsafe_unretained/分配

Possible Duplicate:
strong / weak / retain / unsafe_unretained / assign

在ARC下，unsafe_unretained和弱和分配之间有什么区别? 非常感谢.

what's difference between unsafe_unretained and weak and assign under ARC? thanks a lot.

推荐答案

来自文档:

弱指定一个引用，该引用不能使引用的对象保持活动状态.如果没有强引用，则将弱引用设置为nil 对对象的引用.

weak specifies a reference that does not keep the referenced object alive. A weak reference is set to nil when there are no strong references to the object.

Assign与weak相同，除了它不会将释放实例的指针设置为nil，从而可能留下悬空的指针. Assign和unsafe_unretained的用法相同.

Assign is identical to weak except that it does not set pointers to deallocated instances to nil, potentially leaving dangling pointers. Assign and unsafe_unretained are identical in usage.

噢，我的天，看来我对属性属性和所有权限定词大为困惑；我最初的答案是正确的. Assign和unsafe_unretained都是属性属性，它们暗示其后备实例变量的所有权限定符__unsafe_unretained.使用unsafe_unretained与iOS 4向后兼容，否则使用assign.

Oh my, it seems I massively confused property attributes and ownership qualifiers; my original answer was the correct one. Assign and unsafe_unretained are both property attributes that imply the ownership qualifier __unsafe_unretained for their backing instance variables. Use unsafe_unretained for backwards compatibility with iOS 4 and assign otherwise.

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