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.)
As of iOS 9 (and OS X 10.11), you don't need to remove observers yourself, if you're not using block based observers though. The system will do it for you, since it uses zeroing-weak references for observers, where it can.
A structure that defines the name of a notification.
NotificationCenter.default.addObserver(self, selector: #selector(onDidReceiveData(_:)), name: .didReceiveData, object: nil) This adds an observer with those parameters to the Notification Center, essentially telling it that self wants to observe for notifications with name .
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
...
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
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