What is parameter `object` in NSNotification addObserver:?

Question

One of my class named Message.m is posting a notification with an object sentObject as below

NSDictionary *sentObject = [NSDictionary dictionary         


        

Answer 1

That "object" parameter to "addObserver" is an optional filter. Upon posting a notification you can set an object to the sender of the notification, and will then only be notified of that sender's events. If set to "nil" you will get all notification of this type (regardless who sent them).