创建单例类

.h文件

///创建单例类
+ (instancetype)sharedInstance;
+ (instancetype) alloc __attribute__((unavailable("call sharedInstance instead")));
+ (instancetype) new __attribute__((unavailable("call sharedInstance instead")));
- (instancetype) copy __attribute__((unavailable("call sharedInstance instead")));
- (instancetype) mutableCopy __attribute__((unavailable("call sharedInstance instead")));

.m文件

///单例类
+ (instancetype)sharedInstance{
    
    static POrderGoodsInfoManager *manager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        manager = [[super allocWithZone:NULL] init];
    });
    return manager;
}