blocks|key|251490|text|Short+answer：不，您不必在ARC下的dealloc中将属性设为空。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|251491|Long+answer：dealloc中的属性永远不应该为空，即使是在手动内存管理中也是如此。|251492|在MRR中，你应该释放你的ivars。code属性意味着调用setter，这可能会调用在dealloc中不应该触及的代码(例如，如果您的类或子类覆盖了setter)。类似地，它可能触发KVO通知。相反，释放ivar可以避免这些不受欢迎的行为。|251493|在ARC中，系统会自动为你释放任何dealloc，所以如果这就是你要做的全部事情，你甚至不需要实现ivars。但是，如果您有任何需要特殊处理的非对象dealloc+(例如，您需要对其进行free()的已分配缓冲区)，您仍然必须在ivars中处理它们。|251494|此外，如果您已经将自己设置为任何对象的代理，则应该在dealloc中取消设置该关系(这是调用[obj+setDelegate:nil]的一小部分)。关于在不是用ARC编译的类上这样做的说明是对弱属性的认可。如果该类显式地将其delegate属性标记为weak，那么您就不必这样做了，因为弱属性的性质意味着它将为您详细说明。但是，如果该属性被标记为assign，那么您应该在您的dealloc中将其置零，否则该类将留下一个悬空指针，并且如果它试图向其委托发送消息，则很可能会崩溃。请注意，这仅适用于非保留关系，如委托。|251495|entityMap^0|0|C|O|7|0|0|B|C|7|0|18|7|0|H|7|22|7|2L|6|0|Q|7|1A|L|34|8|3H|4|4T|6|58|7|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|D]]|E|@]|F|$]]|$1|I|3|J|5|6|7|10|8|@$9|11|A|12|B|D]]|E|@]|F|$]]|$1|K|3|L|5|6|7|13|8|@$9|14|A|15|B|D]|$9|16|A|17|B|D]|$9|18|A|19|B|D]]|E|@]|F|$]]|$1|M|3|N|5|6|7|1A|8|@$9|1B|A|1C|B|D]|$9|1D|A|1E|B|D]|$9|1F|A|1G|B|D]|$9|1H|A|1I|B|D]|$9|1J|A|1K|B|D]|$9|1L|A|1M|B|D]]|E|@]|F|$]]|$1|O|3|-4|5|6|7|1N|8|@]|E|@]|F|$]]]|P|$]]

Short answer: no, you do not have to nil out properties in <code>dealloc</code> under ARC.

Long answer: You should never nil out properties in <code>dealloc</code>, even in manual memory management.

In MRR, you should release your ivars. Nilling out properties means calling setters, which may invoke code that it shouldn't touch in <code>dealloc</code> (e.g. if your class, or a subclass, overrides the setter). Similarly it may trigger KVO notifications. Releasing the ivar instead avoids these undesired behaviors.

In ARC, the system automatically releases any ivars for you, so if that's all you're doing you don't even have to implement <code>dealloc</code>. However, if you have any non-object ivars that need special handling (e.g. allocated buffers that you need to <code>free()</code>) you still have to deal with those in <code>dealloc</code>.

Furthermore, if you've set yourself as the delegate of any objects, you should un-set that relationship in <code>dealloc</code> (this is the bit about calling <code>[obj setDelegate:nil]</code>). The note about doing this on classes that aren't compiled with ARC is a nod towards weak properties. If the class explicitly marks its <code>delegate</code> property as <code>weak</code> then you don't have to do this, because the nature of weak properties means it'll get nilled out for you. However if the property is marked <code>assign</code> then you should nil it out in your <code>dealloc</code>, otherwise the class is left with a dangling pointer and will likely crash if it tries to message its delegate. Note that this only applies to non-retained relationships, such as delegates.

blocks|key|251504|text|给出相反的答案..。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|251505|Short+answer：不，你不必在ARC下的dealloc中清除自动合成的属性。对于init中的设置，您不必使用设置器。|offset|length|style|BOLD|CODE|251506|Long+answer：即使在ARC下，你也不应该在dealloc中使用自定义合成的属性。对于init中的设置，您应该使用setter。|251507|关键是您的自定义合成属性应该是安全的，并且在无效方面是对称的。|251508|一个可能的定时器设置器：|251509|-(void)setTimer:(NSTimer+*)timer
{
++++if+(timer+==+_timer)
++++++++return;

++++[timer+retain];
++++[_timer+invalidate];
++++[_timer+release];
++++_timer+=+timer;
++++[_timer+fire];
}|code-block|syntax|javascript|251510|scrollview、tableview、webview、textfield等的可能设置器...：|251511|-(void)setScrollView:(UIScrollView+*)scrollView
{
++++if+(scrollView+==+_scrollView)
++++++++return;

++++[scrollView+retain];
++++[_scrollView+setDelegate:nil];
++++[_scrollView+release];
++++_scrollView+=+scrollView;
++++[_scrollView+setDelegate:self];
}|251512|KVO属性的可能setter：|251513|-(void)setButton:(UIButton+*)button
{
++++if+(button+==+_button)
++++++++return;

++++[button+retain];
++++[_button+removeObserver:self+forKeyPath:@"tintColor"];
++++[_button+release];
++++_button+=+button;
++++[_button+addObserver:self+forKeyPath:@"tintColor"+options:(NSKeyValueObservingOptions)0+context:NULL];
}|251514|这样你就不需要为dealloc，didReceiveMemoryWarning，viewDidUnload，...你的财产就可以安全地公之于众。如果您担心dealloc中的nil+out属性，那么可能是时候再次检查setter了。|251515|entityMap^0|0|0|C|O|7|18|4|0|0|B|Q|7|1B|4|0|0|0|0|0|0|0|0|8|7|G|N|14|D|25|7|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|16|8|@$D|17|E|18|F|G]|$D|19|E|1A|F|H]|$D|1B|E|1C|F|H]]|9|@]|A|$]]|$1|I|3|J|5|6|7|1D|8|@$D|1E|E|1F|F|G]|$D|1G|E|1H|F|H]|$D|1I|E|1J|F|H]]|9|@]|A|$]]|$1|K|3|L|5|6|7|1K|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1L|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|1M|8|@]|9|@]|A|$R|S]]|$1|T|3|U|5|6|7|1N|8|@]|9|@]|A|$]]|$1|V|3|W|5|Q|7|1O|8|@]|9|@]|A|$R|S]]|$1|X|3|Y|5|6|7|1P|8|@]|9|@]|A|$]]|$1|Z|3|10|5|Q|7|1Q|8|@]|9|@]|A|$R|S]]|$1|11|3|12|5|6|7|1R|8|@$D|1S|E|1T|F|H]|$D|1U|E|1V|F|H]|$D|1W|E|1X|F|H]|$D|1Y|E|1Z|F|H]]|9|@]|A|$]]|$1|13|3|-4|5|6|7|20|8|@]|9|@]|A|$]]]|14|$]]

Just to give the opposite answer...

Short answer: no, you don't have to nil out auto-synthesized properties in <code>dealloc</code> under ARC. And you don't have to use the setter for those in <code>init</code>.

Long answer: You should nil out custom-synthesized properties in <code>dealloc</code>, even under ARC. And you should use the setter for those in <code>init</code>.

The point is your custom-synthesized properties should be safe and symmetrical regarding nullification.

A possible setter for a timer:

<pre><code>-(void)setTimer:(NSTimer *)timer
{
 if (timer == _timer)
 return;

 [timer retain];
 [_timer invalidate];
 [_timer release];
 _timer = timer;
 [_timer fire];
}
</code></pre>

A possible setter for a scrollview, tableview, webview, textfield, ...:

<pre><code>-(void)setScrollView:(UIScrollView *)scrollView
{
 if (scrollView == _scrollView)
 return;

 [scrollView retain];
 [_scrollView setDelegate:nil];
 [_scrollView release];
 _scrollView = scrollView;
 [_scrollView setDelegate:self];
}
</code></pre>

A possible setter for a KVO property:

<pre><code>-(void)setButton:(UIButton *)button
{
 if (button == _button)
 return;

 [button retain];
 [_button removeObserver:self forKeyPath:@"tintColor"];
 [_button release];
 _button = button;
 [_button addObserver:self forKeyPath:@"tintColor" options:(NSKeyValueObservingOptions)0 context:NULL];
}
</code></pre>

Then you don't have to duplicate any code for <code>dealloc</code>, <code>didReceiveMemoryWarning</code>, <code>viewDidUnload</code>, ... and your property can safely be made public. If you were worried about nil out properties in <code>dealloc</code>, then it might be time you check again your setters.

I am trying to learn Automatic Reference Counting in iOS 5. Now the first part of this question should be easy:

<ol>
<li>Is it correct that I do NOT need to write explicit
release-property statements in my dealloc when using ARC? In other
words, is it true that the following does NOT need a explicit
dealloc?

<pre><code>@interface MyClass : NSObject
@property (strong, nonatomic) NSObject* myProperty;
@end

@implementation MyClass
@synthesize myProperty;
@end
</code></pre></li>
<li>My next and more important question comes from a line in the <a href="http://developer.apple.com/library/mac/#releasenotes/ObjectiveC/RN-TransitioningToARC/_index.html" rel="noreferrer">Transitioning to ARC Release Notes</a> document:

<blockquote>
 You do not have to (indeed cannot) release instance variables, but you may need to invoke [self setDelegate:nil] on system classes and other code that isn’t compiled using ARC.
</blockquote>

This begs the question: how do I know which system classes are not compiled with ARC? When should I be creating my own dealloc and explicitly setting strongly retaining properties to nil? Should I assume all NS and UI framework classes used in properties require explicit deallocs?</li>
</ol>

There is a wealth of information on SO and elsewhere on the practices of releasing a property's backing ivar when using manual reference tracking, but relatively little about this when using ARC.

Do I set properties to nil in dealloc when using ARC?

内存管理

我正在尝试学习iOS 5中的自动引用计数。现在这个问题的第一部分应该很简单：当使用ARC时，我不需要在我的dealloc中编写显式的release-property语句，这对吗？换句话说，下面这句话是真的吗？不需要显式的dealloc吗？@接口MyClass : NSObject @property (强，非原子) N...

问当使用ARC时，我是否在dealloc中将属性设置为nil？
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问当使用ARC时，我是否在dealloc中将属性设置为nil？
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