// .h文件 #define HMSingletonH(name) + (instancetype)shared##name; // .m文件 #if __has_feature(objc_arc) #define HMSingletonM(name) static id _instace; + (id)allocWithZone:(struct _NSZone *)zone { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ _instace = [super allocWithZone:zone]; }); return _instace; } + (instancetype)shared##name { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ _instace = [[self alloc] init]; }); return _instace; } - (id)copyWithZone:(NSZone *)zone { return _instace; } #else #define HMSingletonM(name) static id _instace; + (id)allocWithZone:(struct _NSZone *)zone { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ _instace = [super allocWithZone:zone]; }); return _instace; } + (instancetype)shared##name { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ _instace = [[self alloc] init]; }); return _instace; } - (id)copyWithZone:(NSZone *)zone { return _instace; } - (oneway void)release { } - (id)retain { return self; } - (NSUInteger)retainCount { return 1;} - (id)autorelease { return self;} #endif
##可以直接连接宏中的参数
如果一条宏太长，以至于一行放不下，就需要在每行的结尾加一个‘\’，表示下一行属于这条宏，和一行中放不下一条
字符串一样
要在arc和mrc模式下都能使用，就需要用预处理宏判断一下
#if __has_feature(objc_arc)
这里放置arc模式下的单例宏
#else
这里放置非arc模式下的单例宏
原文：http://www.cnblogs.com/forflame/p/4558419.html