NSNotification being added multiple times

Question

I have added an observer in viewDidLoad and the issues is if I pop back and come to the same class again, it adds observer multiple times.

Below is the code as how observer is being added:

- (void)viewDidLoad 
  {   
    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"PaymentRecieved" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                        selector:@selector(PaymentRecieved:)
                                            name:@"PaymentRecieved"
                                          object:nil];
  }

The notification is being posted from a different view controller after some processes. Below is the code for the same:

ViewController B:

-(void)CardAccepted  
 {
   [[NSNotificationCenter defaultCenter] postNotificationName:@"PaymentRecieved" object:self userInfo:nil];
 }

The main issue is removeObserver is not working. If I pop back 5 times and then push to same screen 5 times then the observer is added and fired all 5 times.

I have tried everything that was available on Stack Overflow but nothing seems to be working. Below are few of the things that I tried:

Trial 1:

 BOOL isPaymentObserverAdded = [DefaultsValues getBooleanValueFromUserDefaults_ForKey:@"isPaymentObserverAdded"];
 if (!isPaymentObserverAdded) {
 [[NSNotificationCenter defaultCenter] removeObserver:self name:@"PaymentRecieved" object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                        selector:@selector(PaymentRecieved:)
                                            name:@"PaymentRecieved"
                                          object:nil];
  } 

 }

 [DefaultsValues setBooleanValueToUserDefaults:YES ForKey:@"isPaymentObserverAdded"];

Trial 2:

static dispatch_once_t lock;
dispatch_once(&lock, ^{
   [[NSNotificationCenter defaultCenter] addObserver:self
                                        selector:@selector(PaymentRecieved:)
                                            name:@"PaymentRecieved"
                                          object:nil];
});

I know there are so many similar questions on SO for the exact same issue but none of them is solving my problem. Apart from this, I also have couple of other notifications set on this screen.

Can somone please help me to understand what I am doing wrong?

viewDidLoad is not called when you popBAck to the same class. — Teja Nandamuri, Oct 20 '17 at 14:51
observer is added only once. Do you mean notification is being called 5 times ? Where are you calling the CardAccepted method ? — Teja Nandamuri, Oct 20 '17 at 14:53
@TejaNandamuri yes viewDidLoad is not called during pop back but after I pop back, I have to push again to this view to continue process. CardAccepted method is in another view controller. — Milan Gupta, Oct 20 '17 at 16:30
it is fine that way , what do you mean by " fired all 5 times." ? Is it the notification ? — Teja Nandamuri, Oct 20 '17 at 17:02
I am not sure, but `PaymentRecieved ` method is called all 5 times, sometime 3 times, depends how many times I have pushed to the View COntroller. — Milan Gupta, Oct 20 '17 at 17:14
I'm not sure but it *seems* that you want to do something through pushing one ViewController, but then let it only happen once. meaning if the you push the viewController a 2nd time, you don't want it to happen again. Is that right? — mfaani, Oct 23 '17 at 11:23
For this issue I always use this way https://stackoverflow.com/a/5660130/5251783 , please check it . — Hosny, Oct 23 '17 at 13:57

score 0 · Answer 1 · answered Oct 20 '17 at 14:21

0

Instead of removing the observer in your viewDidLoad, you should add it to a dealloc method.

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

This will remove all notification observers the object has subscribed to, and is good practice when using observers with pretty much all custom objects.

answered Oct 20 '17 at 14:21

royalmurder

148
1
10

1

Deregistering in `-dealloc` has not been necessary since iOS 9. – jscs Oct 20 '17 at 14:46

score 0 · Answer 2 · answered Oct 20 '17 at 14:31

0

Try to removeObserver when the user pops from the screen. Like in your back action method.

Like This :

-(void)backAction{

[NSNotificaitonCenter defaultCenter] removeObserver:self name:@"Your Notification name" object:nil]];

}

answered Oct 20 '17 at 14:31

1

BTW why are you using notification center , you can use Custom Delegate. – Oct 20 '17 at 14:45
Thanks for suggestion. Finally I did it with Custom Delegate and it is working fine now. – Milan Gupta Oct 21 '17 at 06:59
Glad i could help you. – Oct 21 '17 at 07:12

score 0 · Answer 3 · answered Oct 23 '17 at 10:55

0

You can remove observer on back button.sure it will work.i solved this issue just a week ago by doing this

answered Oct 23 '17 at 10:55

while register notification do this. [[NSNotificationCenter defaultCenter] removeObserver:self name:@"" object:nil]; [[NSNotificationCenter defaultCenter] postNotificationName:@"" object:dict]; – Oct 24 '17 at 10:04

NSNotification being added multiple times

3 Answers3