blocks|key|21762|text|将此行static+BOOL+initialized+=+NO；放在此行static+MySingleton+*sharedSingleton；下面，如下所示|type|unstyled|depth|inlineStyleRanges|entityRanges|data|21763|static+MySingleton+*sharedSingleton;
static+BOOL+initialized+=+NO;
%2B+(void)initialize
{
++if(!initialized)
++{
+++++initialized+=+YES;
+++++sharedSingleton+=+[[MySingleton+alloc]+init];
++}
}|code-block|syntax|javascript|21764|希望这能有所帮助！|21765|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|$]]

put this line static BOOL initialized = NO; below this line static MySingleton *sharedSingleton; like this

<pre><code>static MySingleton *sharedSingleton;
static BOOL initialized = NO;
+ (void)initialize
{
 if(!initialized)
 {
 initialized = YES;
 sharedSingleton = [[MySingleton alloc] init];
 }
}
</code></pre>

hope that helps!

blocks|key|21782|text|通常的模式是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|21783|static+MySuperclass+*singleton+=+nil;
%2B+(void)initialize+{
++++if+(self+==+[MySuperclass+class])+{
++++++++singleton+=+[[MySubclassProbabl+alloc]+init];
++++}
}|code-block|syntax|javascript|21784|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|$]]

The usual pattern for this is:

<pre><code>static MySuperclass *singleton = nil;
+ (void)initialize {
 if (self == [MySuperclass class]) {
 singleton = [[MySubclassProbabl alloc] init];
 }
}
</code></pre>

blocks|key|3852822|text|更安全的线程选项应该是这样的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3852823|%2B(MySingleton+*)singleton+{
++++static+dispatch_once_t+pred;
++++static+MySingleton+*shared+=+nil;

++++dispatch_once(&pred,+%5E{
++++++++shared+=+[[MySingleton+alloc]+init];
++++});
++++return+shared;
}|code-block|syntax|javascript|3852824|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|$]]

A more thread safe option would be something like:

<pre><code>+(MySingleton *)singleton {
 static dispatch_once_t pred;
 static MySingleton *shared = nil;

 dispatch_once(&amp;pred, ^{
 shared = [[MySingleton alloc] init];
 });
 return shared;
}
</code></pre>

blocks|key|3369776|text|与其他答案略有不同，这是创建单例的现代方法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3369777|static+MySingleton+*+volatile+sharedInstance+=+nil;

%2B(MySingleton*)+sharedInstance+{
++++static+dispatch_once_t+onceToken;
++++dispatch_once(&onceToken,+%5E{
++++++++sharedInstance+=+[[MySingleton+alloc]+init];
++++});

++++return+sharedInstance;
}|code-block|syntax|javascript|3369778|此外，根据您问题的措辞和单例(具有父/子关系)的预期用途，我想说您必须重新考虑您的体系结构。|3369779|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|$]]

A bit different from the other answers, this is the modern way to create a singleton

<pre><code>static MySingleton * volatile sharedInstance = nil;

+(MySingleton*) sharedInstance {
 static dispatch_once_t onceToken;
 dispatch_once(&amp;onceToken, ^{
 sharedInstance = [[MySingleton alloc] init];
 });

 return sharedInstance;
}
</code></pre>

Also, by the wording of your questions and intended use of singletons (with parent/child relationship), I'd say that you have to rethink your architecture.

blocks|key|3369837|text|如果我没理解错的话，你的要求是没有意义的，你似乎混淆了继承的关系。如果您有：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3369838|@interface+Parent+:+NSObject+...
@interface+Child+:+Parent|code-block|syntax|javascript|3369839|那么你创建的每个Child也是一个Parent，是它自身不可分的一部分，没有办法将Parent从Child中分离出来--你只有一个对象。使用继承不会为您提供具有单个共享父项的多个子项。|offset|length|style|CODE|3369840|如果您希望多个子类共享一个父类，那么您的Child类就需要有一个Parent。例如：|3369841|@interface+Parent+:+NSObject+...

@interface+Child+:+NSObject

@property+(readonly)+Parent+*myParent;

-+(id)+initAsChildOf:(Parent+*)parent;

...

@end|3369842|用作：|3369843|Parent+*theParent+=+[Parent+new];
Child+*firstChild+=+[[Child+alloc]+initAsChildOf:theParent];
Child+*secondChild+=+[[Child+alloc]+initAsChildOf:theParent];|3369844|如果你愿意，你可以让Parent成为一个单独的类(只能有一个实例)，或者是一个共享的实例类(一个共享的实例，其他可能的实例)。|3369845|对于继承，而不是关系，很难(但不是不可能;-))从真正的单例类派生，如果这样做，派生类本身就是单例类。|3369846|您可以从共享实例类派生；您可以编写类(再次硬写)，以便您可以拥有且仅有一个实例，该实例不是派生类的实例的一部分。|3369847|注意:到目前为止，其他答案都提供了生成共享实例类的代码，真正的单例类稍微复杂一些(您可以在Apple的文档中找到代码)，通常共享实例类就足够了。|3369848|HTH和我还没有完全误解你的问题！|3369849|entityMap^0|0|0|8|5|H|6|15|6|1C|5|0|K|5|W|6|0|0|0|0|A|6|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|18|8|@$I|19|J|1A|K|L]|$I|1B|J|1C|K|L]|$I|1D|J|1E|K|L]|$I|1F|J|1G|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|1H|8|@$I|1I|J|1J|K|L]|$I|1K|J|1L|K|L]]|9|@]|A|$]]|$1|O|3|P|5|D|7|1M|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|1N|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|1O|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|1P|8|@$I|1Q|J|1R|K|L]]|9|@]|A|$]]|$1|W|3|X|5|6|7|1S|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1T|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1U|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|1V|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|1W|8|@]|9|@]|A|$]]]|15|$]]

If I understand you correctly what you are asking doesn't make sense, you seem to be confusing relationship with inheritance. If you have:

<pre><code>@interface Parent : NSObject ...
@interface Child : Parent
</code></pre>

Then every <code>Child</code> you create is a <code>Parent</code> as well, indivisibly part of itself, there is no way to split the <code>Parent</code> from the <code>Child</code> - you have a single object. Using inheritance does not give you multiple children with a single shared parent.

If you want many children to share a single parent then you need your <code>Child</code> class to have a <code>Parent</code>. For example:

<pre><code>@interface Parent : NSObject ...

@interface Child : NSObject

@property (readonly) Parent *myParent;

- (id) initAsChildOf:(Parent *)parent;

...

@end
</code></pre>

used as:

<pre><code>Parent *theParent = [Parent new];
Child *firstChild = [[Child alloc] initAsChildOf:theParent];
Child *secondChild = [[Child alloc] initAsChildOf:theParent];
</code></pre>

If you wish you can make <code>Parent</code> a singleton class (only one instance possible), or a shared instance class (one shared instance, other instances possible).

With inheritance, as opposed to a relationship, it is hard (but not impossible ;-)) to derive from a true singleton class and if you do so the derived class is itself a singleton. 

You can derive from a shared instance class; and you could write the class (hard again) so that you can have one and only one instance which is not indivisibly part of a instance of a derived class.

Note: the other answers so far have all provided you with code to produce a shared instance class, a true singleton class is a little more involved (you can find the code in Apple's documentation) and often a shared instance class is sufficient.

HTH and I've haven't misunderstood your question completely!

I have a class Parent and a class Child. Child derives from Parent. I only instantiate the Child class, the parent gets never initialized directly, only by the child.
I need at least Parent to be a singleton. If that does not work, Child being a singleton is okay too.
I tried the following but that didn't change it to a singleton:

<pre><code>static MySingleton *sharedSingleton;

+ (void)initialize
{
 static BOOL initialized = NO;
 if(!initialized)
 {
 initialized = YES;
 sharedSingleton = [[MySingleton alloc] init];
 }
}
</code></pre>

The Child class calls [super init] to instantiate the Parent. Can you help me here?

EDIT: I add some background information for my solution (architecture): I have a web service client which has a connection to a web service. I have a base class (Parent) which has information about the connection (authenticated, how to connect etc) and I have different child classes which derive from this base class. The need for different child classes is that one child is responsible for a set of web service logic and another child is responsible for another set of web service logic. The problem is, I want the connection information to be singleton (because they all use only ONE connection, not many).

Objective C Singleton with class hierarchies

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个类Parent和一个类Child。子代派生自父代。我只实例化了child类，父类从不直接初始化，只由子类初始化。我至少需要父母都是独生子女。如果这不起作用，那么Child是一个独生子女也没问题。我尝试了以下方法，但没有将其更改为单例：static MySingleton *sharedSingleton;+ (...

问具有类层次的Objective C Singleton
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