Question

I am looking at a project which was provided me by my organization, for study.

The problem is that in this project I found some code which I never saw before.

Please tell me why the following code is written.

-(void)notifications
{
   [[NSNotificationCenter defaultCenter] addObserver: self selector: 
    @selector(hideViews) name: @"Hide" object:nil]; 
}

This problem arose because this project has only some code for designing.

Sorry if this is a silly question…

Answer 1

You should read up on how notifications work in Cocoa. Consult Apple’s documentation for more information: http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSNotificationCenter_Class/Reference/Reference.html

Basically, NSNotificationCenter is a class that broadcasts NSNotifications from one object to potentially many observing objects. One object can post a notification

[[NSNotificationCenter defaultCenter] postNotificationName:@"NotificationName" object:self];

and other objects can listen for this notification.

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(notificationHandler:) object:theObjectThatPostedTheNotification];

Then, when the first object posts the notification, NSNotificationCenter will notify the other observing object, and notificationHandler: gets called.