一句话实现OC单例模式

首先新建一个头文件,定义如下宏:

// .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 _instace = nil; \
+ (id)allocWithZone:(struct _NSZone *)zone \
{ \
if (_instace == nil) { \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instace = [super allocWithZone:zone]; \
}); \
} \
return _instace; \
} \
\
- (id)init \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instace = [super init]; \
}); \
return _instace; \
} \
\
+ (instancetype)shared##methodName \
{ \
return [[self alloc] init]; \
} \
+ (id)copyWithZone:(struct _NSZone *)zone \
{ \
return _instace; \
} \
\
+ (id)mutableCopyWithZone:(struct _NSZone *)zone \
{ \
return _instace; \
}

#else // 不是ARC

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

#endif

然后在你定义单例类的

.h 文件 写 SingletonH(MyMethodName) 

.m 文件写 SingletonM(MyMethodName)

搞定!