blocks|key|1284283|text|您可以释放您持有的任何子视图，例如，您在loadView方法中保留的UIImageView，或者更好的是该UIImageView上的图像。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1284284|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|$]]

You can release any subviews you hold on to, for example that UIImageView you retained in your loadView method, or better yet the image that was on that UIImageView.

blocks|key|1499182|text|除了已经指出的内容之外，我还想更详细地阐述-viewDidUnload背后的逻辑。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1499183|实现它的一个最重要的原因是，UIViewController子类通常还包含对视图层次结构中各种子视图的引用。例如，这些属性可以在从nib加载时通过IBOutlets设置，或者在-loadView中以编程方式设置。|1499184|UIViewController对子视图的额外所有权意味着，即使将其视图从视图层次结构中移除并释放以节省内存，实际上也不会释放子视图，因为UIViewController本身仍然包含对这些对象的未完成保留引用。释放这些对象的UIViewController额外所有权可确保它们也将被释放以释放内存。|1499185|当UIViewController视图为re-loaded时，您在这里释放的对象通常会重新创建并重新设置，无论是从Nib还是通过-loadView的实现。|1499186|另请注意，在调用此方法时，UIViewController+view属性为nil。|1499187|entityMap^0|L|E|0|E|G|21|9|2G|9|0|0|G|1X|G|34|G|0|1|G|K|9|1S|9|0|D|G|U|4|11|3|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|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|1D|8|@$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|O|$]]

In addition to what has already been indicated, I wanted to elaborate more about logic behind <code>-viewDidUnload</code>. 

One of the most important reasons for implementing it is that <code>UIViewController</code> subclasses commonly also contain owning references to various subviews in the view hierarchy. These properties could have been set through <code>IBOutlets</code> when loading from a nib, or programmatically inside <code>-loadView</code>, for instance.

The additional ownership of subviews by the <code>UIViewController</code> means that even when its view is removed from the view hierarchy and released to save memory, through which the subviews are also released by the view, they will not actually be deallocated because the <code>UIViewController</code> itself still contains its own outstanding retaining references to those objects as well. Releasing the <code>UIViewController</code> additional ownership of these objects ensures they will be deallocated as well to free memory.

The objects that you release here are usually recreated and set again when the <code>UIViewController</code> view is <code>re-loaded</code>, either from a Nib or through an implementation of <code>-loadView</code>.

Also note that the <code>UIViewController</code> <code>view</code> property is <code>nil</code> by the time this method is called.

blocks|key|1499233|text|这是因为您通常会将@property设置为"(nonatomic,+retain)"，因此为您创建的setter将释放当前对象，然后保留参数，即|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1499234|self.property+=+nil;|code-block|syntax|javascript|1499235|...does某物大致如下：|1499236|[property+release];
property+=+[nil+retain];|1499237|因此，您是一举两得:内存管理(释放现有对象)和将指针赋给nil+(因为向nil指针发送任何消息都将返回nil)。|1499238|希望这能有所帮助。|1499239|entityMap^0|9|9|L|L|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|13|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|T|$]]

This is because you will typically set the <code>@property</code> as <code>"(nonatomic, retain)"</code> and as such the setter that is created for you releases the current object and then retains the argument i.e.

<pre><code>self.property = nil;
</code></pre>

...does something along the lines of:

<pre><code>[property release];
property = [nil retain];
</code></pre>

Therefore you are killing two birds with one stone: memory management (releasing the existing object) and assigning the pointer to nil (since sending any message to a nil pointer will return nil).

Hope that helps.

blocks|key|1499310|text|如果视图控制器从导航控制器堆栈中弹出，并且没有保留在其他位置，它将被释放，并且将调用dealloc而不是viewDidUnload。您应该在dealloc中释放在loadView中创建的视图，但没有必要将变量设置为nil，因为在调用dealloc后不久，这些变量将不再存在。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1499311|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 the view controller is popped from the navigation controller stack and is not retained anywhere else, it will be deallocated, and dealloc will be called instead of viewDidUnload. You should release the views created in loadView in dealloc, but it is not necessary to set the variables to nil, because soon after dealloc is called the variables will no longer exist.

What is the <code>-(void)viewDidUnload</code> is good for?

Could I not just relase everything in <code>-dealloc</code>? If the view did unload, wouldn't <code>-dealloc</code> be called anyway?

When should I release objects in -(void)viewDidUnload rather than in -dealloc?

内存管理

-(void)viewDidUnload有什么好处？我能不能在-dealloc中重新发布所有的东西？如果视图确实卸载了，-dealloc不会被调用吗？

问什么时候我应该在-(空)viewDidUnload而不是-dealloc中释放对象？
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问什么时候我应该在-(空)viewDidUnload而不是-dealloc中释放对象？
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