singleton

    //单例化一个类 instanceMothed:单例的方法名称
#define instance_interface(className, instanceMothed)   \
\
+(instancetype)instanceMothed;

    //实现方法
#define instance_implementation(className, instanceMothed)   \
\
static className *_instance;\
\
+(instancetype)instanceMothed\
{   static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [[self alloc]init];\
});\
return _instance;\
}\
\
+(id)allocWithZone:(struct _NSZone *)zone{\
static dispatch_once_t onceToken;\
dispatch_once(&onceToken, ^{\
_instance = [super allocWithZone:zone];\
});\
return _instance;\
}\
\
-(id)copyWithZone:(NSZone *)zone{\
return _instance;\
}