blocks|key|2958535|text|据我所知，就我的运行iOS+5和iOS+4.3的iPhone/iPod而言，这都是自动的。我从4.0开始的一个应用程序，已经“更新”到使用iOS+5.0的Xcode，它从来不会抛出任何关于释放和保留的警告，即使它在每次释放时都会抛出，等等。然而，我插入(复制文件)到用Xcode为iOS+5创建的的新项目中的一些代码有很多很多警告。所以看起来你不必删除所有这些调用，而且不，它以某种方式自动调整它以适应旧版本。分析我的iPod，我没有看到内存泄漏或其他失败的交易/释放的迹象。这有帮助吗？|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2958536|entityMap^0|3P|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

As far as I understand and as far as my iPhone/iPod running iOS 5 and iOS 4.3 respectively work, it's all quite automatic. An app I started for 4.0 and have "updated" to work with Xcode for iOS 5.0 never throws any sort of warning my way about releasing and retaining, even though it's all over every dealloc, etc. However, some of the same code I inserted (copied the file) into a new project created with Xcode for iOS 5 has many, many warnings. So it appears you don't have to remove all those calls, and no, it somehow adapts it automatically for older versions. Profiling my iPod, I see no memory leaks or other signs of failing deallocs/releasing. Does this help?

blocks|key|2958558|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2958559|+如果我决定升级到iOS+5，是否需要从代码中删除所有myObject+retain和myObject+release语句？|blockquote|offset|length|style|BOLD|2958560|2958561|2958562|是的，但是XCode+4.2包含了一个新的“迁移到Objective-C+ARC”工具(在编辑->重构菜单中)，它可以帮你做到这一点。调用dealloc则是另一回事。正如在注释中提到的clang引用，您应该保留dealloc方法：|2958563|理论基础:即使ARC自动销毁实例变量，仍然有合法的理由编写dealloc方法，例如释放不可保留的资源。在这样的方法中调用失败几乎总是一个bug。|2958564|2958565|您可以使用新的-fobjc-编译器标志启用ARC。MacOSXv10.6和v10.7+(64位应用程序)以及iOS+4和iOS+5的Xcode4.2中支持ARC。(MacOSXv10.6和iOS+4中不支持弱引用)。在Xcode+4.1中没有ARC支持。|2958566|2958567|-|2958568|2958569|+如果我使用ARC为iOS+5开发一个新的应用程序，我需要执行某种“追溯兼容性”检查吗？即:我是否需要检查iOS的版本并相应地调用retain和release？那么，基本上，ARC是适用于所有iOS版本，还是只适用于iOS+5?|2958570|2958571|2958572|不是，因为ARC是在编译时而不是在运行时变魔术的。|2958573|2958574|不必记住何时使用保留、释放和自动释放，而是评估对象的生命周期要求，并在编译时自动为您插入适当的方法调用。编译器还会为您生成适当的dealloc方法。|2958575|2958576|2958577|欲了解更多信息，请登录：http://clang.llvm.org/docs/AutomaticReferenceCounting.html。|2958578|entityMap|0|LINK|mutability|MUTABLE|url|http://clang.llvm.org/docs/AutomaticReferenceCounting.html^0|0|1|1P|0|0|0|0|0|0|0|0|0|0|1|35|0|0|0|0|0|0|0|0|C|1M|0|0^^$0|@$1|2|3|-4|4|5|6|1F|7|@]|8|@]|9|$]]|$1|A|3|B|4|C|6|1G|7|@$D|1H|E|1I|F|G]]|8|@]|9|$]]|$1|H|3|-4|4|5|6|1J|7|@]|8|@]|9|$]]|$1|I|3|-4|4|5|6|1K|7|@]|8|@]|9|$]]|$1|J|3|K|4|5|6|1L|7|@]|8|@]|9|$]]|$1|L|3|M|4|5|6|1M|7|@]|8|@]|9|$]]|$1|N|3|-4|4|5|6|1N|7|@]|8|@]|9|$]]|$1|O|3|P|4|C|6|1O|7|@]|8|@]|9|$]]|$1|Q|3|-4|4|5|6|1P|7|@]|8|@]|9|$]]|$1|R|3|S|4|5|6|1Q|7|@]|8|@]|9|$]]|$1|T|3|-4|4|5|6|1R|7|@]|8|@]|9|$]]|$1|U|3|V|4|C|6|1S|7|@$D|1T|E|1U|F|G]]|8|@]|9|$]]|$1|W|3|-4|4|5|6|1V|7|@]|8|@]|9|$]]|$1|X|3|-4|4|5|6|1W|7|@]|8|@]|9|$]]|$1|Y|3|Z|4|5|6|1X|7|@]|8|@]|9|$]]|$1|10|3|-4|4|5|6|1Y|7|@]|8|@]|9|$]]|$1|11|3|12|4|C|6|1Z|7|@]|8|@]|9|$]]|$1|13|3|-4|4|5|6|20|7|@]|8|@]|9|$]]|$1|14|3|-4|4|5|6|21|7|@]|8|@]|9|$]]|$1|15|3|16|4|5|6|22|7|@]|8|@$D|23|E|24|1|25]]|9|$]]|$1|17|3|-4|4|5|6|26|7|@]|8|@]|9|$]]]|18|$19|$4|1A|1B|1C|9|$1D|1E]]]]

<blockquote>
 If I decide to upgrade to iOS 5, do I
 need to remove all [myObject retain]
 and [myObject release] statements from
 my code?
</blockquote>

Yes, but XCode 4.2 includes a new "Migrate to Objective-C ARC" tool (in the Edit->Refactor menu), which does that for you. Calling dealloc is a different story. As mentioned in the comments the clang reference states that you should keep your the dealloc method:

Rationale: even though ARC destroys instance variables automatically, there are still legitimate reasons to write a dealloc method, such as freeing non-retainable resources. Failing to call [super dealloc] in such a method is nearly always a bug.

<blockquote>
 You enable ARC using a new -fobjc-arc
 compiler flag. ARC is supported in
 Xcode 4.2 for Mac OS X v10.6 and v10.7
 (64-bit applications) and for iOS 4
 and iOS 5. (Weak references are not
 supported in Mac OS X v10.6 and iOS
 4). There is no ARC support in Xcode
 4.1. 
</blockquote>

-

<blockquote>
 If I develop a new app for iOS 5 using
 ARC, will I need to implement some
 sort of "retro-compatibility" checks?
 I.e.: will I need to check the version
 of iOS and call retain and release
 accordingly? So, basically, is ARC
 available for all iOS versions or just
 for iOS 5?
</blockquote>

No, because ARC does its magic on compile time and not on run time.

<blockquote>
 Instead of you having to remember when
 to use retain, release, and
 autorelease, ARC evaluates the
 lifetime requirements of your objects
 and automatically inserts the
 appropriate method calls for you at
 compile time. The compiler also
 generates appropriate dealloc methods
 for you.
</blockquote>

Further Information on ARC: <a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html">http://clang.llvm.org/docs/AutomaticReferenceCounting.html</a>

blocks|key|267945|text|关于你问题的这部分|type|unstyled|depth|inlineStyleRanges|entityRanges|data|267946|267947|如果我使用ARC为iOS+5开发一个新的应用程序，我需要实现某种“追溯兼容性”检查吗？即:我是否需要检查iOS的版本并相应地调用retain和release？那么，从根本上说，ARC是适用于所有iOS版本还是只适用于iOS+5？|blockquote|267948|267949|267950|应该注意的是，iOS+5编译器具有“追溯兼容性”(实际上，它添加了代码来使保留/释放工作)，但如果不是针对iOS+5.0进行编译，则不能使用weak作为关键字。相反，您可以使用assign。这是不幸的：weak是一个巨大的优势(永远不会有悬空指针！)。有关weak、assign和ARC的讨论，请参阅我的问题here。|offset|length|style|CODE|267951|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/7246513/zeroing-weak-references-in-arc^0|0|0|0|0|0|1Y|4|2G|6|2T|4|3K|4|3P|6|4A|4|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|W|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|X|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|10|8|@$J|11|K|12|L|M]|$J|13|K|14|L|M]|$J|15|K|16|L|M]|$J|17|K|18|L|M]|$J|19|K|1A|L|M]]|9|@$J|1B|K|1C|1|1D]]|A|$]]|$1|N|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U]]]]

Regarding this part of your question

<blockquote>
 If I develop a new app for iOS 5 using ARC, will I need to implement
 some sort of "retro-compatibility" checks? I.e.: will I need to check
 the version of iOS and call retain and release accordingly? So,
 basically, is ARC available for all iOS versions or just for iOS 5?
</blockquote>

It should be be noted that the iOS 5 compiler takes of the "retro-compatibility" (it actually ADDS the code to make retain/release work, essentially), but if you are not compiling for iOS 5.0, you cannot use <code>weak</code> as a keyword. Instead you use <code>assign</code>. This is unfortunate: <code>weak</code> is a huge advantage (no dangling pointers, ever!). See my question <a href="https://stackoverflow.com/questions/7246513/zeroing-weak-references-in-arc">here</a> for a discussion of <code>weak</code>, <code>assign</code> and ARC.

blocks|key|266317|text|如果您可以通过不使用new+-fobjc-arc编译器标志来禁用ARC，那么您就不会被迫重写向前移动的代码-我猜(?)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|266318|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If you can disable ARC by not using the new -fobjc-arc compiler flag, then you are not forced to re-write code moving forward - I guess (?)

blocks|key|3172598|text|Q1:不，如果你有一个现有的代码，你可以继续使用它和-fno-objc-一样，你可以有选择地在任何文件上禁用ARC。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|3172599|如果你想在多个文件上禁用ARC：|3172600|在Xcode|3172601|PRESS+ENTER中，|unordered-list-item|3172602|在目标/构建阶段/编译源文件中选择所需的文件。(双击仅选择一个文件)键入-fno-objc-arc|ordered-list-item|3172603|Press+|3172604|或|3172605|3172606|3172607|Q2:不能，目标可以低至iOS+4.0|3172608|entityMap^0|Q|A|0|5|2|0|0|0|B|0|10|D|0|0|0|1|0|0|0|0|J|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|15|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|16|8|@$9|17|A|18|B|C]]|D|@]|E|$]]|$1|M|3|N|5|O|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|O|7|1C|8|@]|D|@]|E|$]]|$1|R|3|S|5|O|7|1D|8|@$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]|$1|V|3|W|5|6|7|1I|8|@$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|X|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|Y|$]]

Q1: NO, If you have an existing code, you can keep using it as is with the -fno-objc-arc you can selectively disable ARC on any file. 

If you want to disable ARC on MULTIPLE files:

<ol>
<li>Select desired files at Target/Build Phases/Compile Sources in Xcode</li>
<li>PRESS ENTER. (double click selects only one file)</li>
<li>Type -fno-objc-arc</li>
<li>Press Enter or Done</li>
</ol>

Q2: NO, target can be as low as iOS 4.0

I'm currently developing an app for iPad. The development started for iOS 4.2 and is now continuing (and I think will be completed) for iOS 4.3.
I just read about ARC in iOS 5, and basically I understood that we will never need to release and retain objects anymore. My questions are:

<ol>
<li>If I decide to upgrade to iOS 5, do I need to remove all <code>[myObject retain]</code> and <code>[myObject release]</code> statements from my code?</li>
<li>If I develop a new app for iOS 5 using ARC, will I need to implement some sort of "retro-compatibility" checks? i.e.: will I need to check the version of iOS and call retain and release accordingly? So, basically, is ARC available for all iOS versions or just for iOS 5?</li>
</ol>

Some questions about Automatic Reference Counting in iOS5 SDK

Objective-C

编译器

Xcode

我目前正在为iPad开发一个应用程序。开发开始于iOS 4.2，现在正在继续(我认为将完成) iOS 4.3。我刚刚读到了iOS 5中的ARC，基本上我明白我们再也不需要释放和保留对象了。我的问题是：如果我决定升级到iOS 5，我是否需要从代码中删除所有[myObject retain]和[myObject relea...

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