为了拥有ARC的强大性能，是否需要self.iVar? [英] Is self.iVar necessary for strong properties with ARC?
问题描述
-
如果我声明一个强属性，就像这样:
If I declare a property strong, like so:
@property (strong, nonatomic) UIView *iVar;
设置时，是否执行iVar = ...或self.iVar = ...无关紧要?似乎使用ARC，他们可以做同样的事情.
When I'm setting it, does it matter if I do iVar = ... or self.iVar = ...? It seems that with ARC, they do the same thing.
如果我仅声明实例变量(而不是@property)，例如BOOL selected，是否表示它被推断为__unsafe_unretained(因为没有属性将其指定为强)，或者必须我明确指定了吗?
If I only declare the instance variable (not the @property), e.g., BOOL selected, does that mean it's inferred to be __unsafe_unretained (since there's no property specifying it to be strong), or must I explicitly specify that?
似乎我在回答 ARC:如何释放静态变量?，但是我对上述问题仍然感到困惑.
It seems like I may have answered my own questions above in answering ARC: How to release static variable?, but I'm still slightly confused on the above questions.
推荐答案
从内存管理的角度，使用ivar = ...或self.property = ...(注意:没有 这样的东西self.ivar)是相同的.但是，使用ivar = ...不会调用setter，而使用self.property = ...则会调用setter.这有3个重要的分支，没有特定的顺序:
From a memory management perspective, using ivar = ... or self.property = ... (note: there's no such thing as self.ivar) are the same. However, using ivar = ... doesn't invoke the setter while self.property = ... does. This has 3 important ramifications, in no particular order:
- 如果该属性未标记为
nonatomic，则对基础ivar的访问将不会获得锁定，并且您将破坏原子性的含义. - 如果您或子类重写了该属性，则不会调用该重写的setter.
- 将不会发送KVO通知.
- If the property is not marked
nonatomic, then access to the underlying ivar will not take the lock and you will be breaking the atomicity implications. - If the property is overridden, either by you or by a subclass, the overridden setter will not be invoked.
- KVO notifications will not be sent.
至于仅声明ivar，它具有与声明局部变量相同的内存管理语义. Objective-C自动参考计数文档的第4.4节中对此进行了记录，但基本上，如果它是一个对象，将被推断为__strong.
As for only declaring the ivar, it has the same memory management semantics as declaring a local variable. This is documented in section 4.4 of the Objective-C Automatic Reference Counting document, but basically, if it's an object, it will be inferred to be __strong.
这篇关于为了拥有ARC的强大性能，是否需要self.iVar?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
