Objective-C - 优化这个单例模式？ [英] Objective-C - Optimizing this singleton pattern?

问题描述

我在网上发现了单身模式。在我看来它有很多可以优化的东西。

I've found that singleton pattern on the net. It seems to me it has many things that can be optimized.

-In sharedMySingleton 方法，无需调用保留？我不确定...

- 如果没有，为什么在中保留allocWithZone ？

-what is使用 @synchronized 。 NSAssert认为可以多次调用块，所以如果是的话，应该有更多的代码来释放先前的内存，或者在没有NSAsserting的情况下清楚地退出块，如果没有，为什么会出现这个NSAssert？

- sharedMySingleton 和 alloc 之间的链似乎很奇怪。我给自己写了类似的东西：

-In sharedMySingleton method, no need to call a retain ? I'm not sure...
-If not, why is there a retain in allocWithZone ?
-what is the use of @synchronized. The NSAssert make think that the block can be called many times, so if yes, there should be some more code to release previous memory, or exit the block clearly without just NSAsserting, and if no, why is there this NSAssert ?
-the chain beetween sharedMySingleton and alloc seems strange. I'd wrote myself something like :

+(MySingleton*)sharedMySingleton
{
    @synchronized([MySingleton class])
    {
        if (_sharedMySingleton == nil) _sharedMySingleton = [[self alloc] init];
        return _sharedMySingleton;
    }

    return nil;
}

+(id)alloc
{
    @synchronized([MySingleton class])
    {
        return [super alloc];
    }

    return nil;
} 

单身人士模式

#import "MySingleton.h"

@implementation MySingleton

// ##########################################################################################################
// ######################################## SINGLETON PART ##################################################
// ##########################################################################################################
static MySingleton* _sharedMySingleton = nil;

// =================================================================================================
+(MySingleton*)sharedMySingleton
// =================================================================================================
{
    @synchronized([MySingleton class])
    {
        if (_sharedMySingleton == nil) [[self alloc] init];
        return _sharedMySingleton;
    }

    return nil;
}

// =================================================================================================
+(id)alloc
// =================================================================================================
{
    @synchronized([MySingleton class])
    {
        NSAssert(_sharedMySingleton == nil, @"Attempted to allocate a second instance of a singleton.");
        _sharedMySingleton = [super alloc];
        return _sharedMySingleton;
    }

    return nil;
} 

+ (id)allocWithZone:(NSZone *)zone  { return [[self sharedMySingleton] retain]; }
- (id)copyWithZone:(NSZone *)zone   { return self; }
- (id)retain                        { return self; }
- (NSUInteger)retainCount           { return NSUIntegerMax;  /* denotes an object that cannot be released */}
- (oneway void)release              { /* do nothing */ }
- (id)autorelease                   { return self; }

// ##########################################################################################################
// ##########################################################################################################
// ##########################################################################################################

// =================================================================================================
-(id)init 
// =================================================================================================
{   
    if (!(self = [super init])) return nil;

    return self;
}

// =================================================================================================
-(void) dealloc
// =================================================================================================
{
    [super dealloc];
}

// =================================================================================================
-(void)test 
// =================================================================================================
{
    NSLog(@"Hello World!");
}

@end

推荐答案

你根本不应该使用这种模式（这是一个非常特殊的Singleton案例，你几乎不需要，甚至在这种情况下你通常也不应该使用它。）

You shouldn't use this pattern at all (it's for a very special case of Singleton that you almost never need, and even in that case you generally shouldn't use it).

讨论了很多好的模式我的Objective-C单身看起来像？，但是自GCD发布以来，其中大多数已经过时了。在现代版本的Mac和iOS中，您应该使用以下模式，由Colin Barrett在链接问题中给出：

There are many good patterns discussed at What should my Objective-C singleton look like?, but most of them are outdated since the release of GCD. In modern versions of Mac and iOS, you should use the following pattern, given by Colin Barrett in the linked question:

+ (MyFoo *)sharedFoo
{
    static dispatch_once_t once;
    static MyFoo *sharedFoo;
    dispatch_once(&once, ^{ sharedFoo = [[self alloc] init]; });
    return sharedFoo;
}

我只在这里复制而不是将问题标记为重复，因为旧问题最高 - 答案已过时。

I only copy it here rather than marking the question duplicate because the old question's highest-rated answers are out-dated.

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