NSNotification not being sent when postNotificationName: called
Solution 1
All my code makes use of NSNotifications
like so:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateView) name:@"ScanCompleted" object:nil];
[[NSNotificationCenter defaultCenter] postNotificationName:@"ScanCompleted" object:nil];
The first one is registering the notification and the second posting of the notification.
Solution 2
Basically it's all to do with the order of execution. If you've executed postNotificationName before addObserver, then this is an easy problem to have. Use breakpoints and step through the code :)
Your first breakpoint should stop here:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateView:) name:@"ScanCompleted" object:nil];
Then here:
[[NSNotificationCenter defaultCenter]postNotificationName:@"ScanCompleted" object:self];
Also, make sure the selector has a colon on. Because it's method signature will be:
- (void)updateView:(NSNotification *)notification;
Solution 3
I had the same problem. The reason is that I called removeObserver method at
- (void)viewDidDisappear:(BOOL)animated{
NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
[notificationCenter removeObserver:self];
}
So check whether if you had called removeObserver before postNotification.
Tips: You can search the keyword "removeObserver" to find if you had called this function.
Solution 4
Change this:
[[NSNotificationCenter defaultCenter]postNotificationName:@"Event" object:self];
to this:
[[NSNotificationCenter defaultCenter]postNotificationName:@"Event" object:nil];
If your first notification is registered properly, newEventLoaded should be called.
Solution 5
I had a similar issue and my problem was due to the notification being called on another thread. This solved my problem.
dispatch_async(dispatch_get_main_queue(),^{
[[NSNotificationCenter defaultCenter]postNotificationName:@"Event" object:self];
});
Affian
Updated on February 05, 2020Comments
-
Affian over 4 years
I'm trying to get one instance of using
NSNotificationCenter
withaddObserver
andpostNotificationName
but I can't work out why it won't work.I have 2 lines to code to add the observer and send the message in 2 different classes
[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(newEventLoaded:) name:@"Event" object:nil];
and
[[NSNotificationCenter defaultCenter]postNotificationName:@"Event" object:self];
If I set the name to
nil
it works fine becuase it's just a broadcast, when i try and define a notification name the messages never get through.