iOS单例设计 MRC&ARC

单例设计思想是iOS开发中常见的设计思想之一，下面总结出MRC&ARC环境下单例代码实现：

#import<Foundation/Foundation.h>

@interfaceAccountManager :NSObject <NSCopying>

+ (instancetype)sharedAccountManager;

@end

#import"AccountManager.h"

@implementationAccountManager

staticAccountManager *instance;

#if __has_feature(objc_arc)

// MAEK:在ARC中需要重写以下方法

+ (instancetype)sharedAccountManager
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [[AccountManageralloc]init];
    });
   
    return instance;
}

+ (instancetype)allocWithZone:(struct_NSZone *)zone
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [superallocWithZone:zone];
    });
   
    return instance;
}

- (id)copyWithZone:(NSZone*)zone
{
    return instance;
}

#else

// MAEK:在MRC中除了要重写上面的方法以外还要重写以下方法

+ (instancetype)sharedAccountManager
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [[AccountManager alloc] init];
    });
   
    return instance;
}

+ (instancetype)allocWithZone:(struct_NSZone *)zone
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [superallocWithZone:zone];
    });
   
    return instance;
}

- (id)copyWithZone:(NSZone *)zone
{
    return instance;
}

- (onewayvoid)release
{
    // 什么都不做
}

- (instancetype)retain
{
    return instance;
}

- (instancetype)autorelease
{
    return instance;
}

///永远保证引用计数为1
- (NSUInteger)retainCount
{
    return 1;
}

#endif

@end