Post of NSNotificationCenter causing "EXC_BAD_ACCESS" exception

Question

A UIViewController adds itself to the default center:

[[NSNotificationCenter defaultCenter]
 addObserver:self
 selector:@selector(editFood)
 name:@"editFood"
 object:nil];

Then a UITableView delegate NSObject posts a NSNotification:

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

During run time it get a EXC_BAD_ACCESS exception.

Is the defaultCenter getting released somewhere? The same concept works when I post a notification to a UIViewController from a UIViewController, but that shouldn't matter, right?

adding `[[NSNotificationCenter defaultCenter] removeObserver:self]` to `-(void)dealloc{}` method in your Scene will probably solve this problem for you. It worked for me; I was having the same problem you were. Good luck! — nodebase, Sep 22 '14 at 02:05

score 131 · Answer 1 · answered Apr 14 '11 at 19:44

131

One of your subscribers has been deallocated. Make sure to call [[NSNotificationCenter defaultCenter] removeObserver:self] in your dealloc (if not sooner).

answered Apr 14 '11 at 19:44

Ben Scheirman

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3

Thanks, I just realized my mistake (After looking at this and researching for four hours). The object I was attempting to reference after the call had been released. The debugger just made it look like that's where the EXC_BAD_ACCESS exception was being thrown. – Paul Jordan Apr 14 '11 at 19:51
4

@Paul: The Zombies instrument is really helpful in debugging this kind of problem. – Sven Apr 14 '11 at 19:59
@Sven Thanks, I appreciate it. I actually tried using that once, and couldn't figure out how. I added an environment variable in the project plist, but that wouldn't work. – Paul Jordan Apr 14 '11 at 20:44
i'm releasing that object after notification called i got EXC_BAD_ACCESS how can i solve that? – jpd Mar 06 '13 at 05:39
3

EXC_BAD_ACCESS is not an exception, it's invalid memory access – junglecat Oct 21 '13 at 09:16

score 11 · Answer 2 · answered Oct 13 '14 at 06:10

EXC_BAD_ACCESS can happen even after verifying dealloc exists like so:

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

The above will solve the problem most of the time, but apparently my cause was that I was indirectly adding the observer with a selector: set to nil as follows:

[NSNotificationCenter.defaultCenter addObserver:self
                                         selector:nil
                                             name:notificationName
                                           object:nil];

...so when I posted something with that notificationName, EXC_BAD_ACCESS occurred.

The solution was to send a selector that actually points to something.

Yup, just found this myself, I had put `NULL` as the selector intending it to be temporary, like oh let me go create that method, then I forgot to go update the selector param later (DOH) and yep, EXC_BAD_ACCESS result. — Billy Gray, Oct 20 '14 at 14:52

score 1 · Answer 3 · answered Oct 13 '20 at 16:34

1

I had the same issue in Swift. The problem was the function target had a closure parameter with default value:

@objc func performFoo(completion: (() -> Void)? = nil) {
   ...
}

After I replace the closure parameter with a Notification parameter, it worked:

@objc func performFoo(notification: Notification) {
    ...
}

I had to make some refactor to make it works in a right way.

answered Oct 13 '20 at 16:34

pableiros

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Yes, the documentation for `NotificationCenter addObserver(_:selector:name:object:)` does state: *"The method that aSelector specifies must have one and only one argument (an instance of NSNotification)."*. – HangarRash Aug 28 '23 at 06:25

score 0 · Answer 4 · answered Apr 20 '23 at 18:02

0

For anyone getting this error and using async/await, be sure to check if this other issue might not be the cause https://stackoverflow.com/a/76066999/2828729

tl;dr: at the time of writing @objc selectors and async methods don't go well together

answered Apr 20 '23 at 18:02

aclima

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score 0 · Answer 5 · answered Jun 29 '23 at 04:49

0

With the introduction of async/await, be also careful for your selectors to not have the async keyword.

answered Jun 29 '23 at 04:49

Vladimir

521
5
16

arc4randall · Answer 6 · 2023-08-28T20:00:11.683

0

This error can also occur with the wrong method header. I just got the error by not accepting an object when the notification was sending an object.

NotificationCenter.default.post(name: MyNotification.name, object: self)

Will work with:

@objc func myFunction(_ sender: AnyObject) {}

But not with

@objc func myFunction() {}

NOTE: This was edited to have the functions not be "async throws" which will cause a sporadic crash.

edited Aug 28 '23 at 20:00

answered Aug 28 '23 at 01:59

arc4randall

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Yes, the documentation for `NotificationCenter addObserver(_:selector:name:object:)` does state: *"The method that aSelector specifies must have one and only one argument (an instance of NSNotification)."*. And I'm not sure using an `async throws` method is a good idea for a function marked with `@objc`. See the more recent answers about that. – HangarRash Aug 28 '23 at 06:23
You are right! This causes an intermittent crash. I had to change this from being async throws. Its deceptive because it doesn't crash every time. – arc4randall Aug 28 '23 at 19:59

Post of NSNotificationCenter causing "EXC_BAD_ACCESS" exception

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