blocks|key|1719440|text|这取决于你所说的“私有”是什么意思。在Objective-C中，调用对象上的方法可能更好地描述为向该对象发送消息。该语言中没有任何内容禁止客户端对对象调用任何给定的方法；您所能做的最好的事情就是不在头文件中声明该方法。如果客户端仍然使用正确的签名调用"private“方法，它仍然会在运行时执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1719441|也就是说，在Objective-C中创建私有方法的最常见方法是在实现文件中创建一个Category，并在其中声明所有的“隐藏”方法。请记住，这并不能真正阻止对init的调用，但如果有人试图这样做，编译器将发出警告。|offset|length|style|CODE|1719442|MyClass.m|1719443|@interface+MyClass+(PrivateMethods)
-+(NSString*)+init;
@end

@implementation+MyClass

-+(NSString*)+init
{
++++//+code...
}

@end|code-block|syntax|javascript|1719444|在MacRumors.com上有一个关于这个话题的不错的thread。|1719445|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/Articles/chapter_4_section_1.html|1|http://forums.macrumors.com/showthread.php?t=470056^0|0|27|4|15|8|0|0|0|0|S|6|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@$D|12|E|13|F|G]]|9|@$D|14|E|15|1|16]]|A|$]]|$1|H|3|I|5|6|7|17|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|18|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|19|8|@]|9|@$D|1A|E|1B|1|1C]]|A|$]]|$1|Q|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]|Y|$5|T|U|V|A|$W|Z]]]]

That depends on what you mean by "make private". In Objective-C, calling a method on an object might better be described as sending a message to that object. There's nothing in the language that prohibits a client from calling any given method on an object; the best you can do is not declare the method in the header file. If a client nevertheless calls the "private" method with the right signature, it will still execute at runtime.

That said, the most common way to create a private method in Objective-C is to create a <a href="http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/Articles/chapter_4_section_1.html" rel="nofollow noreferrer">Category</a> in the implementation file, and declare all of the "hidden" methods in there. Remember that this won't truly prevent calls to <code>init</code> from running, but the compiler will spit out warnings if anyone tries to do this.

MyClass.m

<pre><code>@interface MyClass (PrivateMethods)
- (NSString*) init;
@end

@implementation MyClass

- (NSString*) init
{
 // code...
}

@end
</code></pre>

There's a decent <a href="http://forums.macrumors.com/showthread.php?t=470056" rel="nofollow noreferrer">thread</a> on MacRumors.com about this topic.

blocks|key|1504367|text|如果你谈论的是默认的-init方法，那么你就不能这么做，因为它是从NSObject继承的，每个类都会响应它而不会发出任何警告。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1504368|你可以创建一个新的方法，比如说-initMyClass，然后把它放在一个私有的类别中，就像马特建议的那样。然后定义默认的-init方法，要么在被调用时引发异常，要么(最好)使用一些默认值调用您的私有-initMyClass。|1504369|人们似乎想要隐藏init的一个主要原因是为了singleton+objects。如果是这种情况，那么您不需要隐藏-init，只需返回单例对象(如果它还不存在，则创建它)。|offset|length|1504370|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/chapter_3_section_10.html^0|0|0|M|H|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

If you are talking about the default -init method then you can't. It's inherited from NSObject and every class will respond to it with no warnings.

You could create a new method, say -initMyClass, and put it in a private category like Matt suggests. Then define the default -init method to either raise an exception if it's called or (better) call your private -initMyClass with some default values. 

One of the main reasons people seem to want to hide init is for <a href="http://developer.apple.com/documentation/Cocoa/Conceptual/CocoaFundamentals/CocoaObjects/chapter_3_section_10.html" rel="nofollow noreferrer">singleton objects</a>. If that's the case then you don't need to hide -init, just return the singleton object instead (or create it if it doesn't exist yet).

blocks|key|1719579|text|Objective-C和Smalltalk一样，没有“私有”和“公共”方法的概念。任何消息都可以在任何时间发送到任何对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1719580|如果您的-init方法被调用，您可以做的是抛出一个NSInternalInconsistencyException：|offset|length|style|CODE|1719581|-+(id)init+{
++++[self+release];
++++@throw+[NSException+exceptionWithName:NSInternalInconsistencyException
+++++++++++++++++++++++++++++++++++reason:@"-init+is+not+a+valid+initializer+for+the+class+Foo"
+++++++++++++++++++++++++++++++++userInfo:nil];
++++return+nil;
}|code-block|syntax|javascript|1719582|另一种选择-在实践中可能要好得多-是如果可能的话，让-init为您的类做一些明智的事情。|1719583|如果您尝试这样做是因为您试图“确保”使用单例对象，那么请不要费心。具体地说，不要为创建单例的“覆盖%2BallocWithZone:，-init，-retain，-release”方法而烦恼。它实际上总是不必要的，只是增加了复杂性，没有真正的显着优势。|1719584|相反，只需编写代码，使您的%2BsharedWhatever方法就是您访问单例的方式，并将其作为在头中获取单例实例的方式进行记录。在绝大多数情况下，这应该就是您所需要的全部。|1719585|entityMap^0|0|4|5|P|W|0|0|Q|5|0|1D|F|1T|5|1Z|7|27|8|0|D|F|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@$D|W|E|X|F|G]|$D|Y|E|Z|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|11|8|@$D|12|E|13|F|G]]|9|@]|A|$]]|$1|O|3|P|5|6|7|14|8|@$D|15|E|16|F|G]|$D|17|E|18|F|G]|$D|19|E|1A|F|G]|$D|1B|E|1C|F|G]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1D|8|@$D|1E|E|1F|F|G]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|T|$]]

Objective-C, like Smalltalk, has no concept of "private" versus "public" methods. Any message can be sent to any object at any time.

What you can do is throw an <code>NSInternalInconsistencyException</code> if your <code>-init</code> method is invoked:

<pre><code>- (id)init {
 [self release];
 @throw [NSException exceptionWithName:NSInternalInconsistencyException
 reason:@"-init is not a valid initializer for the class Foo"
 userInfo:nil];
 return nil;
}
</code></pre>

The other alternative — which is probably far better in practice — is to make <code>-init</code> do something sensible for your class if at all possible.

If you're trying to do this because you're trying to "ensure" a singleton object is used, don't bother. Specifically, don't bother with the "override <code>+allocWithZone:</code>, <code>-init</code>, <code>-retain</code>, <code>-release</code>" method of creating singletons. It's virtually always unnecessary and is just adding complication for no real significant advantage.

Instead, just write your code such that your <code>+sharedWhatever</code> method is how you access a singleton, and document that as the way to get the singleton instance in your header. That should be all you need in the vast majority of cases.

blocks|key|1504613|text|你不能让它成为“私有/不可见”的问题是因为初始化方法被发送给id+(因为alloc返回一个id)，而不是YourClass|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1504614|请注意，从编译器(检查器)的角度来看，id可以潜在地响应任何键入的内容(它不能在运行时检查id中真正包含的内容)，所以只有当没有任何地方(publicly+=+in+header)使用init方法时，您才可以隐藏init，而不是编译器知道，id没有办法响应init，因为到处都没有init+(在您的源代码中，所有的库等等……)|1504615|因此，您不能禁止用户传递init并被编译器破坏...但是，您可以做的是防止用户通过调用init来获取真实的实例|1504616|简单地实现init，它返回nil并有一个(私有的/不可见的)初始化器，这个初始化器的名字是其他人不会得到的(比如initOnce，initWithSpecial+...)|1504617|static+SomeClass+*+SInstance+=+nil;

-+(id)init
{
++++//+possibly+throw+smth.+here
++++return+nil;
}

-+(id)initOnce
{
++++self+=+[super+init];
++++if+(self)+{
++++++++return+self;
++++}
++++return+nil;
}

%2B+(SomeClass+*)+shared+
{
++++if+(nil+==+SInstance)+{
++++++++SInstance+=+[[SomeClass+alloc]+initOnce];
++++}
++++return+SInstance;
}|code-block|syntax|javascript|1504618|注意:有人可以做到这一点|1504619|SomeClass+*+c+=+[[SomeClass+alloc]+initOnce];|1504620|它实际上会返回一个新的实例，但如果initOnce在我们的项目中没有公开声明(在标题中)，它将生成一个警告(id可能不会响应...)无论如何，使用它的人需要确切地知道真正的初始化器是initOnce|1504621|我们可以进一步防止这种情况，但没有必要|1504622|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|12|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

well the problem why you can't make it "private/invisible" is cause the init method gets send to id (as alloc returns an id) not to YourClass 

Note that from the point of the compiler (checker) an id could potencialy respond to anything ever typed (it can't check what really goes into the id at runtime), so you could hide init only when nothing nowhere would (publicly = in header) use a method init, than the compile would know, that there is no way for id to respond to init, since there is no init anywhere (in your source, all libs etc...)

so you cannot forbid the user to pass init and get smashed by the compiler... but what you can do, is to prevent the user from getting a real instance by calling a init

simply by implementing init, which returns nil and have an (private / invisible) initializer which name somebody else won't get (like initOnce, initWithSpecial ...)

<pre><code>static SomeClass * SInstance = nil;

- (id)init
{
 // possibly throw smth. here
 return nil;
}

- (id)initOnce
{
 self = [super init];
 if (self) {
 return self;
 }
 return nil;
}

+ (SomeClass *) shared 
{
 if (nil == SInstance) {
 SInstance = [[SomeClass alloc] initOnce];
 }
 return SInstance;
}
</code></pre>

Note : that somebody could do this

<pre><code>SomeClass * c = [[SomeClass alloc] initOnce];
</code></pre>

and it would in fact return a new instance, but if the initOnce would nowhere in our project be publicly (in header) declared, it would generate a warning (id might not respond ...) and anyway the person using this, would need to know exactly that the real initializer is the initOnce

we could prevent this even further, but there is no need

blocks|key|1719809|text|我不得不提到，在子类中放置断言和引发异常来隐藏方法对于好心的人来说是一个令人讨厌的陷阱。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1719810|我推荐使用__unavailable作为Jano+explained+for+his+first+example。|offset|length|style|CODE|1719811|方法可以在子类中被覆盖。这意味着如果超类中的方法使用的方法只是在子类中引发异常，那么它可能不会按预期工作。换句话说，你刚刚打破了过去有效的东西。初始化方法也是如此。下面是这种相当常见的实现的一个示例：|1719812|-+(SuperClass+*)initWithParameters:(Type1+*)arg1+optional:(Type2+*)arg2
{
++++...bla+bla...
++++return+self;
}

-+(SuperClass+*)initWithLessParameters:(Type1+*)arg1
{
++++self+=+[self+initWithParameters:arg1+optional:DEFAULT_ARG2];
++++return+self;
}|code-block|syntax|javascript|1719813|想象一下，如果我在子类中这样做，-initWithLessParameters会发生什么：|1719814|-+(SubClass+*)initWithParameters:(Type1+*)arg1+optional:(Type2+*)arg2
{
++++[self+release];
++++[super+doesNotRecognizeSelector:_cmd];
++++return+nil;
}|1719815|这意味着您应该倾向于使用私有(隐藏)方法，特别是在初始化方法中，除非您计划重写这些方法。但是，这是另一个话题，因为您并不总是完全控制超类的实现。(这让我质疑__attribute((objc_designated_initializer))的使用是不好的实践，尽管我没有深入使用它。)|1719816|它还意味着您可以在必须在子类中重写的方法中使用断言和异常。(+Creating+an+abstract+class+in+Objective-C中的“抽象”方法)|1719817|还有，不要忘了%2Bnew类方法。|1719818|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/5772821/2400328|1|https://stackoverflow.com/questions/1034373/creating-an-abstract-class-in-objective-c^0|0|5|D|K|10|0|0|0|0|0|0|0|V|15|1|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@$D|1A|E|1B|F|G]]|9|@$D|1C|E|1D|1|1E]]|A|$]]|$1|H|3|I|5|6|7|1F|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|1G|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|1H|8|@]|9|@]|A|$]]|$1|Q|3|R|5|L|7|1I|8|@]|9|@]|A|$M|N]]|$1|S|3|T|5|6|7|1J|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1K|8|@]|9|@$D|1L|E|1M|1|1N]]|A|$]]|$1|W|3|X|5|6|7|1O|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]|16|$5|11|12|13|A|$14|17]]]]

I have to mention that placing assertions and raising exceptions to hide methods in the subclass has a nasty trap for the well-intended.

I would recommend using <code>__unavailable</code> as <a href="https://stackoverflow.com/a/5772821/2400328">Jano explained for his first example</a>.

Methods can be overridden in subclasses. This means that if a method in the superclass uses a method that just raises an exception in the subclass, it probably won't work as intended. In other words, you've just broken what used to work. This is true with initialization methods as well. Here is an example of such rather common implementation:

<pre><code>- (SuperClass *)initWithParameters:(Type1 *)arg1 optional:(Type2 *)arg2
{
 ...bla bla...
 return self;
}

- (SuperClass *)initWithLessParameters:(Type1 *)arg1
{
 self = [self initWithParameters:arg1 optional:DEFAULT_ARG2];
 return self;
}
</code></pre>

Imagine what happens to -initWithLessParameters, if I do this in the subclass:

<pre><code>- (SubClass *)initWithParameters:(Type1 *)arg1 optional:(Type2 *)arg2
{
 [self release];
 [super doesNotRecognizeSelector:_cmd];
 return nil;
}
</code></pre>

This implies that you should tend to use private (hidden) methods, especially in initialization methods, unless you plan to have the methods overridden. But, this is another topic, since you don't always have full control in the implementation of the superclass. (This makes me question the use of __attribute((objc_designated_initializer)) as bad practice, although I haven't used it in depth.)

It also implies that you can use assertions and exceptions in methods that must be overridden in subclasses. (The "abstract" methods as in <a href="https://stackoverflow.com/questions/1034373/creating-an-abstract-class-in-objective-c">Creating an abstract class in Objective-C</a> )

And, don't forget about the +new class method.

blocks|key|1504793|text|Apple已经开始在它们的头文件中使用以下内容来禁用init构造函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1504794|-+(instancetype)init+NS_UNAVAILABLE;|code-block|syntax|javascript|1504795|这在Xcode中正确地显示为编译器错误。具体地说，这是在它们的几个HealthKit头文件(HKUnit是其中之一)中设置的。|1504796|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Apple has started using the following in their header files to disable the init constructor:

<pre><code>- (instancetype)init NS_UNAVAILABLE;
</code></pre>

This correctly displays as a compiler error in Xcode. Specifically, this is set in several of their HealthKit header files (HKUnit is one of them).

blocks|key|1504865|text|将此文件放在头文件中|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1504866|-+(id)init+UNAVAILABLE_ATTRIBUTE;|code-block|syntax|javascript|1504867|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Put this in header file

<pre><code>- (id)init UNAVAILABLE_ATTRIBUTE;
</code></pre>

I need to hide (make private) the <code>-init</code> method of my class in Objective-C.

How can I do that?

Is it possible to make the -init method private in Objective-C?

Objective-C

编译器

Xcode

我需要在Objective-C中隐藏(设置为私有)类的-init方法。我该怎么做呢？

问是否可以在Objective-C中将-init方法设为私有？
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