How to retrieve all NSNotificationCenter observers?

Question

I'd like to retrieve a list of observers (objects and selectors) for a given notification name. I know there's no official API for that. I also know I could subclass NSNotificationCenter to accomplish this. Sometimes however this is not a viable option because NSNotificationCenter usage is spread all over the code or even binary frameworks.

So I'm looking for an unofficial/private way to do this. (Since it's about debugging only, that's fine.)

You may just want to swizzle the methods so you get the object: http://cocoadev.com/wiki/MethodSwizzling — rckoenes, Nov 07 '12 at 14:14
here is an answer which implements swizzling to track observers http://stackoverflow.com/questions/10346700/nsnotificationcenter-list-of-observers/34692724#34692724 — Zayin Krige, Jan 09 '16 at 11:32

Ortwin Gentz · Accepted Answer · 2015-11-25T09:29:40.693

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Finally, Apple added a way to print all notification center observers:

po [NSNotificationCenter defaultCenter]

It prints a comma separated list with Name, Object, Observer, and Options:

<NSNotificationCenter:0x7f997b307500>
Name, Object, Observer, Options
WebPreferencesRemovedNotification, 0x11165b680, 0x116c87ff8, 1400
UIApplicationWillEnterForegroundNotification, 0x11165b680, 0x7f997a838000, 1400
...

edited Nov 25 '15 at 09:29

answered Nov 25 '15 at 09:22

Ortwin Gentz

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score 1 · Answer 2 · edited May 23 '17 at 12:10

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If you don't want to subclass NSNotificationCenter you can rename original addObserver:selector:name:object method and create your own with such name and add observers in there to some array then call original renamed method.

Take a look at following methods: class_addMethod, class_replaceMethod, class_getMethodImplementation.

Also look at this SO question: Method Swizzling

I am not sure why you want observers but you might find this class useful, which removes observers automatically for you which I think might be what you want. SFObservers

edited May 23 '17 at 12:10

Community

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answered Nov 07 '12 at 14:16

Tomasz Zabłocki

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+1 for `SFObservers`! The SO question you're pointing to is actually from me (including the solution) ;-) – Ortwin Gentz Nov 07 '12 at 21:55
Hahah, nice solution & question though:D – Tomasz Zabłocki Nov 07 '12 at 21:57
here is an answer which implements swizzling to track observers http://stackoverflow.com/questions/10346700/nsnotificationcenter-list-of-observers/34692724#34692724 – Zayin Krige Jan 09 '16 at 11:31

How to retrieve all NSNotificationCenter observers?

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