直接宣告為singleton的.h

到時只要import這個.h，就可以用這個方法宣告

#define SYNTHESIZE_SINGLETON_FOR_HEADER(className) \

\

+ (className *)shared##className;

#define SYNTHESIZE_SINGLETON_FOR_CLASS(className) \

\

+ (className *)shared##className { \

static className *shared##className = nil; \

static dispatch_once_t onceToken; \

dispatch_once(&onceToken, ^{ \

shared##className = [[self alloc] init]; \

}); \

return shared##className; \

}