blocks|key|2307566|text|要针对旧操作系统，您可以在属性声明中使用unsafe_unretained而不是weak，并且它的工作方式应该大致相同。当目标消失时，weak引用本身为零，但unsafe_unretained留下了一个可能性，即当您正在链接的对象被释放时，它可能会变成一个悬空指针。后者的行为与您在手动内存管理中使用assign作为属性声明的行为相同。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2307567|这样做是为了避免保留周期，我在回答here时提到了这一点。您不希望有一个强指针指向可能有强指针返回到原始对象的东西。那么什么都不会得到适当的释放。|2307568|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/6260256/what-kind-of-leaks-does-objective-cs-automatic-reference-counting-in-xcode-4-2/6388601#6388601^0|K|H|14|4|1V|4|27|H|46|6|0|H|4|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@$9|11|A|12|1|13]]|E|$]]|$1|H|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

To target the older OS, you can use <code>unsafe_unretained</code> instead of <code>weak</code> in your property declaration, and it should mostly work the same way. <code>weak</code> references nil themselves when their target goes away, but <code>unsafe_unretained</code> leaves open the possibility that the object you're linking to could turn into a dangling pointer when it is deallocated. The latter is the same behavior as if you had used <code>assign</code> as a property declaration in manual memory management.

You do this to avoid retain cycles, which I mention in my answer <a href="https://stackoverflow.com/questions/6260256/what-kind-of-leaks-does-objective-cs-automatic-reference-counting-in-xcode-4-2/6388601#6388601">here</a>. You don't want to have a strong pointer to something that might have a strong pointer back to the original object. Then nothing would get released properly.

blocks|key|2307576|text|如果只使用弱引用来增加安全性，那么如果新的运行时函数可用，就手动调用它们，如果没有，则手动调用__unsafe_unretained变量的简单赋值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2307577|ZWRCompatibility.h将在一定程度上简化这一点。|2307578|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/rpetrich/ZWRCompatibility^0|1B|J|0|0|I|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@]|D|@$9|T|A|U|1|V]]|E|$]]|$1|H|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

If only using weak references for additional safety, manually call the new runtime functions if they're available and fallback to simple assignment on <code>__unsafe_unretained</code> variables if not.

<a href="https://github.com/rpetrich/ZWRCompatibility">ZWRCompatibility.h</a> will simplify this somewhat.

blocks|key|2288051|text|感谢Mike的兼容性库PLWeakCompatibilty，您现在也可以在iOS+4.x上使用__weak。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2288052|它非常容易配置，并且不需要在5.x上进行额外的考虑或工作。|2288053|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/plausiblelabs/PLWeakCompatibility^0|B|I|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

Thanks to Mike Ash's compatibility library <a href="https://github.com/plausiblelabs/PLWeakCompatibility">PLWeakCompatibilty</a>, you can now simply use __weak on iOS 4.x, as well.

It's incredibly easy to configure and requires no additional consideration or effort over 5.x.

I've begun developing my first iOS app with Xcode 4.2, and was targeting iOS 5.0 with a "utility application" template (the one that comes with a FlipsideViewController). 

I read that since ARC is a compile-time feature, it should be compatible with iOS 4 as well, so I attempted to target my app to 4.3, and try compiling it. When I do so, I get this error:

FlipsideViewController.m: error: Automatic Reference Counting Issue: The current deployment target does not support automated __weak references

It is referencing this line:

<pre><code>@synthesize delegate = _delegate;
</code></pre>

That variable is declared as:

<pre><code>@property (weak, nonatomic) IBOutlet id &lt;FlipsideViewControllerDelegate&gt; delegate;
</code></pre>

I understand that "weak references" are not supported in iOS 4, but I don't really understand why I would want to use a weak reference to begin with, nor can I figure out how I would rewrite things to avoid using it, while still taking advantage of ARC (after all, it's supposed to work with iOS 4 AND 5 right?)

How do I replace weak references when using ARC and targeting iOS 4.0?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我已经开始用Xcode 4.2开发我的第一个iOS应用程序，并使用一个“实用程序”模板(随FlipsideViewController附带的模板)将iOS 5.0作为目标。我读到，由于ARC是一个编译时特性，它也应该与iOS 4兼容，所以我尝试将我的应用程序定位为4.3，并尝试编译它。当我这样做时，我会得到以下错误： ...

问如何在使用ARC和以iOS 4.0为目标时替换弱引用？
EN

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问如何在使用ARC和以iOS 4.0为目标时替换弱引用？EN