blocks|key|3251331|text|如果您使用的是现代Objective-C运行时(即iOS+3.x或更高版本，或者64位雪豹或更高版本)，那么在这种情况下，您不需要为您的属性定义ivar。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3251332|当您@synthesize属性时，ivar实际上也将为您合成。这就绕过了"fragile-ivar“场景。你可以在Cocoa+with+Love上阅读更多关于它的内容|offset|length|style|CODE|3251333|entityMap|0|LINK|mutability|MUTABLE|url|http://cocoawithlove.com/2010/03/dynamic-ivars-solving-fragile-base.html^0|0|2|B|1L|F|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@$D|R|E|S|F|G]]|9|@$D|T|E|U|1|V]]|A|$]]|$1|H|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

If you are using the Modern Objective-C Runtime (that's either iOS 3.x or greater, or 64-bit Snow Leopard or greater) then you do not need to define ivars for your properties in cases like this.

When you <code>@synthesize</code> the property, the ivar will in effect be synthesized also for you. This gets around the "fragile-ivar" scenario. You can read more about it on <a href="http://cocoawithlove.com/2010/03/dynamic-ivars-solving-fragile-base.html" rel="noreferrer">Cocoa with Love</a>

blocks|key|3037170|text|在您的接口中，您可以在大括号之间正式声明实例变量，或者通过大括号外的@property声明实例变量，或者两者兼而有之。无论哪种方式，它们都会成为类的属性。不同之处在于，如果您声明@property，那么您可以使用@synthesize实现，它会自动为您编写getter/setter代码。例如，自动编码器设置器初始化整数并将浮点数设置为零。如果您声明了一个实例变量，但没有指定相应的@property，那么您就不能使用@synthesize，而必须编写您自己的getter/setter。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|3037171|您总是可以通过指定自己的getter/setter来覆盖自动编码的getter/setter。这通常是使用延迟加载的managedObjectContext属性完成的。因此，您需要将managedObjectContext声明为一个属性，然后还要编写一个-(NSManagedObjectContext+*)managedObjectContext方法。回想一下，与实例变量/属性同名的方法是"getter“方法。|3037172|@property声明方法还允许您使用其他选项，如retain和readonly，而实例变量声明方法不支持这些选项。基本上，ivar是旧的方式，@property对其进行了扩展，并使其更花哨/更容易。你可以使用self来引用这两种方法。前缀或非前缀，只要名称对于该类是唯一的就无关紧要了。否则，如果您的超类具有与您相同的属性名称，那么您必须说like+self.name或super.name，以便指定您正在讨论的名称。|3037173|因此，您将看到越来越少的人在大括号之间声明ivar，而是转向只指定@property，然后执行@synthesize。如果没有相应的@property，就不能在实现中执行@synthesize。合成器只从@property规范中知道它是什么类型的属性。synthesize语句还允许您重命名属性，以便您可以在代码中使用一个名称(速记)来引用属性，而在.h文件中使用全名。然而，有了XCode现在拥有的非常酷的自动补全功能，这并不是一个优势，但它仍然存在。|3037174|希望这有助于澄清所有的困惑和错误的信息，到处都是。|3037175|entityMap^0|Y|9|2H|9|2Y|B|5B|9|5T|B|66|2|0|1M|K|2J|K|3J|1B|0|0|9|P|6|W|8|1Q|4|20|9|0|L|4|X|9|1B|B|1U|9|2D|B|2U|9|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]]|E|@]|F|$]]|$1|I|3|J|5|6|7|1A|8|@$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]]|E|@]|F|$]]|$1|K|3|L|5|6|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]|$9|1S|A|1T|B|C]|$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]]|E|@]|F|$]]|$1|M|3|N|5|6|7|1Y|8|@]|E|@]|F|$]]|$1|O|3|-4|5|6|7|1Z|8|@]|E|@]|F|$]]]|P|$]]

In your interface, you can formally declare an instance variable between the braces, or via <code>@property</code> outside the braces, or both. Either way, they become attributes of the class. The difference is that if you declare <code>@property</code>, then you can implement using <code>@synthesize</code>, which auto-codes your getter/setter for you. The auto-coder setter initializes integers and floats to zero, for example. IF you declare an instance variable, and DO NOT specify a corresponding <code>@property</code>, then you cannot use <code>@synthesize</code> and must write your own getter/setter. 

You can always override the auto-coded getter/setter by specifying your own. This is commonly done with the <code>managedObjectContext</code> property which is lazily loaded. Thus, you declare your <code>managedObjectContext</code> as a property, but then also write a <code>-(NSManagedObjectContext *)managedObjectContext</code> method. Recall that a method, which has the same name as an instance variable/property is the "getter" method. 

The <code>@property</code> declaration method also allows you other options, such as <code>retain</code> and <code>readonly</code>, which the instance variable declaration method does not. Basically, <code>ivar</code> is the old way, and <code>@property</code> extends it and makes it fancier/easier. You can refer to either using the self. prefix, or not, it doesn't matter as long as the name is unique to that class. Otherwise, if your superclass has the same name of a property as you, then you have to say either like self.name or super.name in order to specify which name you are talking about. 

Thus, you will see fewer and fewer people declare <code>ivar</code>s between the braces, and instead shift toward just specifying <code>@property</code>, and then doing <code>@synthesize</code>. You cannot do <code>@synthesize</code> in your implementation without a corresponding <code>@property</code>. The Synthesizer only knows what type of attribute it is from the <code>@property</code> specification. The synthesize statement also allows you to rename properties, so that you can refer to a property by one name (shorthand) inside your code, but outside in the .h file use the full name. However, with the really cool autocomplete that XCode now has, this is less of an advantage, but is still there. 

Hope this helps clear up all the confusion and misinformation that is floating around out there.

blocks|key|3037264|text|从文档中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3037265|一般来说，属性的行为在现代运行时和传统运行时都是相同的(请参阅Objective-C运行时编程指南中的“运行时版本和平台”)。有一个关键的区别:现代运行时支持实例变量合成，而传统运行时不支持。|3037266|要使@synthesize在遗留运行时中工作，您必须提供一个与该属性具有相同名称和兼容类型的实例变量，或者在@synthesize语句中指定另一个现有的实例变量。在现代运行库中，如果不提供实例变量，编译器会为您添加一个。|3037267|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

From the documentation: 

In general the behavior of properties is identical on both modern and legacy runtimes (see “Runtime Versions and Platforms” in Objective-C Runtime Programming Guide). There is one key difference: the modern runtime supports instance variable synthesis whereas the legacy runtime does not.

For @synthesize to work in the legacy runtime, you must either provide an instance variable with the same name and compatible type of the property or specify another existing instance variable in the @synthesize statement. With the modern runtime, if you do not provide an instance variable, the compiler adds one for you.

blocks|key|3037286|text|这两种方法都有效，但是如果不在花括号中声明它们，就不会在xcode的调试器中看到它们的值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3037287|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|$]]

it works both ways but if you don't declare them in the curly braces, you won't see their values in the debugger in xcode.

blocks|key|304416|text|The+Objective-C+Programming+Language:+Property+Implementation+Directives|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|304417|304418|根据运行时的不同，访问器合成的行为也会有所不同(另请参阅“运行时差异”)：|blockquote|304419|304420|304421|对于传统运行时，实例变量必须已在当前类的@|304422|块中声明。如果存在与属性同名的实例变量，并且其类型与属性的类型兼容，则会使用该变量，否则会出现编译器错误。|unordered-list-item|304423|
|304424|对于现代运行时(请参阅Objective-C运行时编程指南中的“运行时版本和平台”)，会根据需要合成实例变量。如果已存在同名的实例变量，则使用该变量。|304425|304426|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocProperties.html^0|0|20|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|D|3|-4|5|6|7|15|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|16|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|17|8|@]|9|@]|C|$]]|$1|I|3|-4|5|6|7|18|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|19|8|@]|9|@]|C|$]]|$1|L|3|M|5|N|7|1A|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|1B|8|@]|9|@]|C|$]]|$1|Q|3|R|5|N|7|1C|8|@]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1D|8|@]|9|@]|C|$]]|$1|T|3|-4|5|6|7|1E|8|@]|9|@]|C|$]]]|U|$V|$5|W|X|Y|C|$Z|10]]]]

<a href="https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocProperties.html" rel="nofollow">The Objective-C Programming Language: Property Implementation Directives</a>

<blockquote>
 There are differences in the behavior of accessor synthesis that depend on the runtime (see also “Runtime Difference”):
 
 <ul>
 <li>For the legacy runtimes, instance variables must already be declared in the @interface block of the current class. If an instance variable of the same name as the property exists, and if its type is compatible with the property’s type, it is used—otherwise, you get a compiler error.</li>
 <li>For the modern runtimes (see “Runtime Versions and Platforms” in Objective-C Runtime Programming Guide), instance variables are synthesized as needed. If an instance variable of the same name already exists, it is used.</li>
 </ul>
</blockquote>

blocks|key|3251672|text|如果您使用的是XCode+4.4或更高版本，它将为您生成实例变量合成代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3251673|您只需像下面这样声明属性；它将为您生成合成代码和实例变量声明代码。|3251674|@property+(nonatomic,+strong)+NSString+*name;|code-block|syntax|javascript|3251675|它将生成合成代码，如|3251676|@synthesize+name+=+_name;|3251677|您可以使用_name访问实例变量，它类似于声明|3251678|NSString*+_name|3251679|但如果声明为只读属性，则如下所示|3251680|@property+(nonatomic,+strong,+readonly)+NSString+*name;|3251681|它将生成代码|3251682|@synthesize+name;|3251683|或|3251684|@synthesize+name+=+name;+|3251685|所以你应该访问没有前缀"_“的即时变量名，你可以写你自己的合成代码，然后编译器会为你生成代码。你可以写|3251686|@synthesize+name+=+_name;|3251687|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1B|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1D|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1F|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|1G|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|1H|8|@]|9|@]|A|$]]|$1|W|3|X|5|F|7|1I|8|@]|9|@]|A|$G|H]]|$1|Y|3|Z|5|6|7|1J|8|@]|9|@]|A|$]]|$1|10|3|11|5|F|7|1K|8|@]|9|@]|A|$G|H]]|$1|12|3|13|5|6|7|1L|8|@]|9|@]|A|$]]|$1|14|3|15|5|F|7|1M|8|@]|9|@]|A|$G|H]]|$1|16|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|17|$]]

If you are using XCode 4.4 or later it will generate instance variable synthesizing code for you. 

You just have to declare properties like below; it will generate synthesizing code and instance variable declaring code for you.

<pre><code>@property (nonatomic, strong) NSString *name;
</code></pre>

it will generate synthesizing code as 

<pre><code>@synthesize name = _name;
</code></pre>

and you can access instance variable using _name
it is similar to declare 

<pre><code>NSString* _name
</code></pre>

but if you declare read-only property it like

<pre><code>@property (nonatomic, strong, readonly) NSString *name;
</code></pre>

it will generate code 

<pre><code>@synthesize name;
</code></pre>

or 

<pre><code>@synthesize name = name; 
</code></pre>

So you should access instant variable name with out prefix "_"
any way you can write your own synthesizing code then compiler will generate code for you.
you can write 

<pre><code>@synthesize name = _name;
</code></pre>

Do properties in Objective-C 2.0 require a corresponding instance variable to be declared? For example, I'm used to doing something like this:

MyObject.h

<pre><code>@interface MyObject : NSObject {
NSString *name;
}
@property (nonatomic, retain) NSString *name;
@end
</code></pre>

MyObject.m

<pre><code>@implementation
@synthesize name;
@end
</code></pre>

However, what if I did this instead:

MyObject.h

<pre><code>@interface MyObject : NSObject {
}
@property (nonatomic, retain) NSString *name;
@end
</code></pre>

Is this still valid? And is it in any way different to my previous example?

Do declared properties require a corresponding instance variable?

Objective-C

编译器

调试器

Objective-C2.0中的属性是否需要声明相应的实例变量？例如，我习惯于这样做：MyObject.h@interface MyObject : NSObject {NSString *name;}@property (nonatomic, retain) NSString *name;@endMyObject.m...

问声明的属性是否需要相应的实例变量？
EN

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问声明的属性是否需要相应的实例变量？
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