Objective-C ARC:强 vs 保留和弱 vs 分配 [英] Objective-C ARC: strong vs retain and weak vs assign

问题描述

ARC 引入的属性有两个新的内存管理属性，strong 和 weak.

There are two new memory management attributes for properties introduced by ARC, strong and weak.

除了copy，这显然是完全不同的东西，strong vs retain 和 有什么区别吗?弱 vs assign?

Apart from copy, which is obviously something completely different, are there any differences between strong vs retain and weak vs assign?

根据我的理解，这里唯一的区别是 weak 会将 nil 分配给指针，而 assign 不会，这意味着一旦指针被释放，当我向指针发送消息时，程序就会崩溃.但是如果我使用 weak，这将永远不会发生，因为发送到 nil 的消息不会做任何事情.

From my understanding, the only difference here is that weak will assign nil to the pointer, while assign won't, which means the program will crash when I send a message to the pointer once it's been released. But if I use weak, this won't ever happen, because message send to nil won't do anything.

我不知道 strong 和 retain 之间有什么区别.

I don't know about any differences between strong and retain.

有什么理由让我在新项目中使用 assign 和 retain 或者是被弃用的那种?

Is there any reason why should I use assign and retain in new projects, or are the kind of being deprecated?

推荐答案

来自 过渡到 ARC 发行说明(属性属性部分中的示例).

From the Transitioning to ARC Release Notes (the example in the section on property attributes).

// The following declaration is a synonym for: @property(retain) MyClass *myObject;

@property(strong) MyClass *myObject;

所以 strong 与属性声明中的 retain 相同.

So strong is the same as retain in a property declaration.

对于 ARC 项目，我将使用 strong 而不是 retain，我将使用 assign 用于 C 原始属性和 weak 用于对 Objective-C 对象的弱引用.

For ARC projects I would use strong instead of retain, I would use assign for C primitive properties and weak for weak references to Objective-C objects.

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