addObserver:selector:name:object: Adds an entry to the receiver’s dispatch table with an observer, a notification selector and optional criteria: notification name and sender.

• (void)addObserver:(id)notificationObserver selector:(SEL)notificationSelector name:(NSString *)notificationName object:(id)notificationSender Parameters 。。。。 。。。。 notificationSender The object whose notifications the observer wants to receive; that is, only notifications sent by this sender are delivered to the observer.

If you pass nil, the notification center doesn’t use a notification’s sender to decide whether to deliver it to the observer.

很明显，此object 是用于过滤Notication的，只接收指定Sender所发的Notification

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(finishReadNFC:) name:@"NotificationFinishReadNFC" object:self];

发送notification端：

[[NSNotificationCenter defaultCenter]   postNotificationName:@"NotificationFinishReadNFC" object:self userInfo:[NSDictionary dictionaryWithObject:item forKey:NotificationKeySaveItem]];

参数放在userinfo里传送，而不是object

Resource Reference

• http://blog.csdn.net/ljuncong/article/details/8059717