NSNotificationCenter crashes my app

Question

I've added a NSNotificationCenter observer that calls 2 selectors with the same name on two different view controllers.

It works, but when I run the app sometimes it crashes with this error message:

Thread 1: EXC_BAD_ACCESS (code=1, address=0x18)

or

Thread 1: EXC_BAD_ACCESS (code=EXC_I386_GPFLT)

Anyone has an idea why it crashes? Thank you!

.

My code:

fetchFromParse:

-(void)sendAllStores
{
    [[NSNotificationCenter defaultCenter]postNotificationName:@"getStoresArrays" object:nil userInfo:self.storesDict];
}

firstVC.m:

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

-(void)getStoresArrays:(NSNotification*)notification
{
    NSLog(@“Working”);  
}

secondVC.m:

-(void)prepareArrays
{
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(getStoresArrays:) name:@"getStoresArrays" object:nil];
}
-(void)getStoresArrays:(NSNotification*)notification
{
    NSLog(@“Working”);
}

AppDelegate.m:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.secVC=[[secondVC alloc] init];
    [self.secVC prepareArrays];

    fetchFromParse *fetchFromParseObj=[[fetchFromParse alloc] init];
    [fetchFromParseObj getStoresFromParse];

    Return YES;
}

Add an exception breakpoint to get more specific information — vadian, Jan 27 '16 at 15:18
@vadian It's crashes every time elsewhere and sometimes it's not even crashes. — FS.O, Jan 27 '16 at 16:35
Have you checked that `self.storesDict` is not nil before trying to include it as user info of the notification? Is `self.secVC` on the app delegate declared as a `strong` property? — John Rogers, Jan 28 '16 at 03:07
@JohnRogers `self.storesDict` is not nil. And yes, both `secVC` and `firstVC` are strong properties. — FS.O, Jan 28 '16 at 10:04

score 3 · Answer 1 · answered Feb 03 '16 at 12:10

Notification Crashes

Typically you might see a crash of this nature if you attempt to close a view controller without removing the observer. So that part of the answer provided by Mr. Patil, is absolutely required. Your use-case will vary about where and how you remove the observer. If you remove it too soon you might end up crashing if you try to reference any related objects.

So you might want to remove the self.storesDict object or at least verify that it is not nil before using it.

Debugging

Here's a quick tutorial on debugging with Xcode. It's for an older version but it should get you up to speed quickly. You can also review Apple docs for more on collecting crash logs.

Logs

You should go to the reports navigator and copy a bit more of your log so that we can determine a more precise cause of the issue. You can add a breakpoint right before the faulty code and then step through the issue. Copy the debug console if nothing else.

Getting the crash log

You can open Xcode go the Window menu select Devices. Select your attached device (iPhone/iPad) and click the View Device Logs button. From the list select your app name/crash date. Copy the data to the question.

More Information

The more information you provide on crashes the more likely we can help you. I suspect that the answer is you are either trying to access something that is nil or not releasing the observer at the right time. It might not be appropriate to release the observer when your view disappears but you have not provided enough information to make that obvious.

How do the different view controllers work together? Are you certain that the Notifications is causing the crash?? Put a breakpoint at the post notification and in each selector and then debug the app until it crashes. You will need to identify the conditions that precede the crash. I'll refine this answer if you let me know when you update the question.

ascendancy05 · Answer 2 · 2016-01-28T02:32:06.387

1

First thing I would do is do a global search and make sure no other classes are listening to that notification. Then I would make sure that in the classes that you have added an observer for that notification you do the following:

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

edited Jan 28 '16 at 02:32

answered Jan 27 '16 at 15:08

ascendancy05

227
2
16

score 0 · Answer 3 · answered Jan 27 '16 at 14:14

0

Add this

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];

    //Has to be unregistered always, otherwise nav controllers down the line will call this method
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

hope it helps.

answered Jan 27 '16 at 14:14

Pradumna Patil

2,180
3
17
46

Still crashing, any other idea? – FS.O Jan 27 '16 at 14:17
you can try this in viewDidUnload method – Pradumna Patil Jan 27 '16 at 14:18
But viewDidUnload deprecated on iOS 6 – FS.O Jan 27 '16 at 14:19
No problem still you can use this. – Pradumna Patil Jan 27 '16 at 14:21
Any other idea? Please! – FS.O Jan 27 '16 at 14:26
check this link http://stackoverflow.com/questions/5668752/post-of-nsnotificationcenter-causing-exc-bad-access-exception . – Pradumna Patil Jan 27 '16 at 14:28
Tries to add it on -dealloc method and it's still crashing!! – FS.O Jan 27 '16 at 14:36
You must balance the addObserver... and removeObserver... calls. I recommend -init and -dealloc. – Nicolas Miari Jan 27 '16 at 14:49
Otherwise, make sure that viewDidLoad is being executed exactly once. – Nicolas Miari Jan 27 '16 at 14:49
Also, make sure the action you registered matches the signature of your notification hadler method (including colons). – Nicolas Miari Jan 27 '16 at 14:51
@NicolasMiari I don't think I understand, can you please post a code example to help me understand what you mean? Thanks! – FS.O Jan 27 '16 at 14:51
I'm on a smartphone now. Instead, update your question with the code you use to register for the notification, and the method you expect to have called. – Nicolas Miari Jan 27 '16 at 14:53
@NicolasMiari OK, I've updated the post with my code, please take a look. Thank you very much for helping! – FS.O Jan 27 '16 at 14:58
Since the observer is being added in `viewDidLoad`, using `viewWillDisappear` to remove the observer is a bad idea since `viewDidLoad` is only called once but `viewWillDisappear` can be called multiple times. Use `dealloc` instead. – rmaddy Jan 27 '16 at 15:57
@rmaddy I have tried `dealloc` (on firstVC, secondVC and even both at the same time) and it's still crashing – FS.O Jan 27 '16 at 16:31
Have you verified `dealloc` is called? – rmaddy Jan 27 '16 at 16:32
@rmaddy Oh, it's not called for some reason. What can it be? – FS.O Jan 27 '16 at 16:44
@FS.O Probably a reference cycle. – rmaddy Jan 27 '16 at 16:47
@rmaddy What does it mean? And how can I fix it? – FS.O Jan 27 '16 at 16:49
@rmaddy Can you please help me? – FS.O Jan 28 '16 at 09:58

score 0 · Answer 4 · answered Jan 27 '16 at 23:45

0

Are you sure that 'addObserver', 'postNotification' and 'removeObserver' are always called on the main thread?

Please doublecheck with:

if ([NSThread isMainThread])

answered Jan 27 '16 at 23:45

OlDor

1,460
12
18

NSNotificationCenter crashes my app

4 Answers4

Notification Crashes

Debugging

Logs

More Information