学习笔记 - 两行代码创建单例

利用两行代码创建单例

// 帮助实现单例设计模式

// .h文件的实现
#define SingletonH(methodName) + (instancetype)shared##methodName;

// .m文件的实现
#if __has_feature(objc_arc) // 是ARC
#define SingletonM(methodName) \
static id _instance = nil; \
+ (id)allocWithZone:(struct _NSZone *)zone \
{ \
if (_instance == nil) { \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [super allocWithZone:zone]; \
}); \
} \
return _instance; \
} \
\
- (id)init \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [super init]; \
}); \
return _instance; \
} \
\
+ (instancetype)shared##methodName \
{ \
return [[self alloc] init]; \
} \
+ (id)copyWithZone:(struct _NSZone *)zone \
{ \
return _instance; \
} \
\
+ (id)mutableCopyWithZone:(struct _NSZone *)zone \
{ \
return _instance; \
}

#else // 不是ARC

#define SingletonM(methodName) \
static id _instance = nil; \
+ (id)allocWithZone:(struct _NSZone *)zone \
{ \
if (_instance == nil) { \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [super allocWithZone:zone]; \
}); \
} \
return _instance; \
} \
\
- (id)init \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [super init]; \
}); \
return _instance; \
} \
\
+ (instancetype)shared##methodName \
{ \
return [[self alloc] init]; \
} \
\
- (oneway void)release \
{ \
\
} \
\
- (id)retain \
{ \
return self; \
} \
\
- (NSUInteger)retainCount \
{ \
return 1; \
} \
+ (id)copyWithZone:(struct _NSZone *)zone \
{ \
    return _instance; \
} \
 \
+ (id)mutableCopyWithZone:(struct _NSZone *)zone \
{ \
    return _instance; \
}

#endif