How to retrieve all NSNotificationCenter observers

问题:

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.)

回答1:

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
...

回答2:

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