单例模式:
//static id _instace; // //+ (id)allocWithZone:(struct _NSZone *)zone //{ // static dispatch_once_t onceToken; // dispatch_once(&onceToken, ^{ // _instace = [super allocWithZone:zone]; // }); // return _instace; //} // // //- (id)copyWithZone:(NSZone *)zone //{ // return _instace; //} // //+ (instancetype)sharedInstance //{ // static dispatch_once_t onceToken; // dispatch_once(&onceToken, ^{ // _instace = [[self alloc] init]; // }); // return _instace; //}