Cocoa Custom Notification Example

Question

Can someone please show me an example of a Cocoa Obj-C object, with a custom notification, how to fire it, subscribe to it, and handle it?

Vague question. Try asking a more specific question, or search Apple's documentation. — danielpunkass, May 10 '09 at 04:52
I wouldn't normally comment on a question like this, but seeing as how you received a "con" then mine can be a "pro". This question allows for a *concise* answer dealing strictly with the topic. I merely want to find out one simple thing - not *scour* apple's documentation (which would most likely be worth-while anyway). So thanks for asking this question. I see your +15 atm on the question being congruent with my sentiment. — Jacksonkr, Mar 26 '12 at 18:58
Here is a app that i wrote, it might help you https://github.com/kylelk/Notification-example/tree/master — kyle k, Nov 03 '13 at 02:14

score 82 · Accepted Answer · answered May 09 '09 at 05:25

82

@implementation MyObject

// Posts a MyNotification message whenever called
- (void)notify {
  [[NSNotificationCenter defaultCenter] postNotificationName:@"MyNotification" object:self];
}

// Prints a message whenever a MyNotification is received
- (void)handleNotification:(NSNotification*)note {
  NSLog(@"Got notified: %@", note);
}

@end

// somewhere else
MyObject *object = [[MyObject alloc] init];
// receive MyNotification events from any object
[[NSNotificationCenter defaultCenter] addObserver:object selector:@selector(handleNotification:) name:@"MyNotification" object:nil];
// create a notification
[object notify];

For more information, see the documentation for NSNotificationCenter.

answered May 09 '09 at 05:25

Jason Coco

77,985
20
184
180

What's the point of using notification then? Why not just call [object handleNotification] straight? – user4951 May 28 '12 at 15:44
3

Loose coupling. Note the "// somewhere else" comment... The notification is a kind of broadcast message. Any object instance can listen to a notification and doesn't need to conform to any particular delegate protocol or similar. There may be many instances listening to a single message. The sender doesn't need to have pointers to the object instance(s) it wishes to notify. – Andrew Hodgkinson Jul 07 '12 at 08:22

score 45 · Answer 2 · edited Jun 22 '10 at 13:34

Step 1:

//register to listen for event    
[[NSNotificationCenter defaultCenter]
  addObserver:self
  selector:@selector(eventHandler:)
  name:@"eventType"
  object:nil ];

//event handler when event occurs
-(void)eventHandler: (NSNotification *) notification
{
    NSLog(@"event triggered");
}

Step 2:

//trigger event
[[NSNotificationCenter defaultCenter]
    postNotificationName:@"eventType"
    object:nil ];

score 6 · Answer 3 · answered Dec 10 '12 at 16:18

Make sure to unregister notification (observer) when your object is deallocated. Apple documentation states: "Before an object that is observing notifications is deallocated, it must tell the notification center to stop sending it notifications".

For Local Notifications the next code is applicable:

[[NSNotificationCenter defaultCenter] removeObserver:self];

And for observers of distributed notifications:

[[NSDistributedNotificationCenter defaultCenter] removeObserver:self];

Cocoa Custom Notification Example

3 Answers3

Linked