NSNotification not removing observers

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NSNotification not removing observers

(6 posts) (3 voices)

Started 2 years ago by javy
Latest reply from macgeo

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javy
Member
Searched and searched, but couldn't find the answer. Maybe it's related to Cocos2d? Probably not - it's likely just my bad coding skills!

I'm using NSNotificationCenter to let me know when a button is pressed in my app. Maybe not the best way to use the service, but I'm experimenting trying to get it to work.

In my Layer, I have the following code:
```
#define kLeftButtonNotify	@"Left Button"
```
And in the custom init method for the Layer:
```
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(onLeftPress:) name:kLeftButtonNotify object:sprite];
```
'sprite' is an AtlasSprite that has been sub-classed to allow it to do some extra things when it's touched. One of the things is this:
```
[[NSNotificationCenter defaultCenter] postNotificationName:notifyName object:self];
```
'notifyName' is retained in the sprite itself on creation, being passed kLeftButtonNotify.

The app works fine. Notifications are posted and received properly.

The problem comes in removing the Layer as an observer. When I change views using 'replaceScene', then return to this view using replaceScene once again, the notification is received twice, as if it was not removed as an observer.

Each time I change and return to this scene with this layer, it keeps increasing the number of notifications I get.

In the dealloc method of the Layer:
```
[[NSNotificationCenter defaultCenter] removeObserver:self];
```
I've also tried:
```
AtlasSpriteCustom *sprite = (AtlasSpriteCustom *)[self getChildByTag:kLeftButtonTag];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:kLeftButtonNotify object:sprite];
```
...but it doesn't make any difference.

Thanks for any help!
Posted 2 years ago #
crmagicxxx
Member

Hi

I'll not comment your need for notifications, and if it could be done better...

First, be sure that your dealloc method is called at all. Maybe you have some unreleased things in your layer that prevents calling dealloc. Second, it's important if you're calling [[NSNotificationCenter defaultCenter] removeObserver:self] before or after [super dealloc], because you're maybe sending message to nil. Anyway, I'd try calling removeObserver in onExit method and see if that helps... I am using NSNotificationCenter in mu custom made class for dealing with ads, and it works without problems

One more thing came up to my mind now... Try calling [[NSNotificationCenter defaultCenter] removeObserver:self] in your init method, just before you do [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(onLeftPress:) name:kLeftButtonNotify object:sprite];. That way it'll be removed from NSNotificationCenter for sure.

Though, according to your problems I am almost sure that your layer is not dealloced properly. But last method I suggested you will make your notifications working anyway

Posted 2 years ago #
javy
Member
Thanks for your help in this, I really do appreciate it.

I tried remove observer as you suggested in the init method, but the selector is still called an increasing multiple number of times whenever the scene is replaced.

I did an NSLog and the dealloc method is being called:
```
- (void) dealloc
{
	[self unschedule:@selector(tickAnimate:)];

	// release registrations for notifications
	[[NSNotificationCenter defaultCenter] removeObserver:self];

	NSLog(@"******** dealloc!!! *********");

	[super dealloc];
}
```
Perhaps I'm not releasing objects correctly as you suggested. In my Scene, I have this code as well:
```
- (void) dealloc
{
	[self removeAllChildrenWithCleanup:YES];
	[super dealloc];
}
```
I should note that the AtlasSprite sub-class (& manager) is retained somewhere else in code by another class, but I don't think this would have any bearing on the layer having itself registered as an observer. After all, the AtlasSprite only posts a message and doesn't have a direct link to the layer class itself. When the layer is deallocated, the other part of the code still has the sprite, but the layer gives up its references.

I've never used notifications before, so I admit I'm a bit puzzled this. I think I'm doing it right, but I've no idea what's wrong.

Thanks for all your help!
Posted 2 years ago #
crmagicxxx
Member

Well, I am not sure. Only thing that's logical is that "self" in [[NSNotificationCenter defaultCenter] addObserver:self ... is not the same "self" as in [[NSNotificationCenter defaultCenter] removeObserver:self]

So, try with NSLog(@"%@", self); just before you addObserver and before you removeObserver and compare it...

Hey, something more just came up to my mind. Maybe your sprite is actually the problem, sending notifications twice for some reason? So when you register your layer as observer it automatically get's two messages? Where and when in your sprite code you actually send notifications? Observer is just an observer. So it's possible that your sprite is sending more notifications than it should, and your layer is not responsible for receiving more messages than it needs. If you can't trace the send notification problem, you can always tell your Layer to receive just one message and the remove itself as observer (with simple BOOL)...

I would like to help more but without the whole code it's pretty impossible. Maybe it's some trivial mistake somewhere else that messes the whole thing.

Btw, I still don't get it why you're using notifications at all? Can't you just define simple methods that will communicate between your sprites and layer?

Posted 2 years ago #
javy
Member
'Maybe your sprite is actually the problem, sending notifications twice for some reason?'

This got me thinking. An NSLog showed the button being pressed twice (from the class itself), but the layer receiving it only once.

So maybe the sprite isn't released properly? I'm almost certain it is, but I could be wrong.

The scene that has the layer has this in dealloc:
```
[self removeAllChildrenWithCleanup:YES];
```
I'm under the impression that this will tell the sprite manager added to the layer to dealloc the sprites that were added as children, yes?

My custom sprite also uses the TargetedTouchDelegate protocol.
```
[[TouchDispatcher sharedDispatcher] addTargetedDelegate:self priority:0 swallowsTouches:NO];
```
This is how it gets the messages, and in the dealloc method:
```
[[TouchDispatcher sharedDispatcher] removeDelegate:self];
```
I will keep hunting but any further insight is welcome (if it isn't to annoying already)!

BTW - I could do away with the notifications as you suggest, but I would like to figure out what's wrong - for future knowledge.

Thanks again
Posted 2 years ago #
macgeo
Member

I fixed my version of this problem by putting [[NSNotificationCenter defaultCenter] removeObserver:self] in -(void) onExit, not in dealloc...

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

Posted 2 months ago #

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