CODEWITHSUNDEEP
iosswiftnsnotificationcenter
ma11hew28
ma11hew28

Reputation: 126319

How to list all notifications that an object is observing?

Is it possible to list all the notifications that an object is observing via NotificationCenter?

Upvotes: 3

Views: 681

Answers (2)

Phillip Mills
Phillip Mills

Reputation: 31016

You could do it by parsing [[NSNotificationCenter defaultCenter] debugDescription] and searching for object addresses:

  • Name, Object, Observer, Options
  • NSWindowWillEnterFullScreenNotification, 0x7fffb685e8e0, 0x6000001003f0, 1400
  • _NSWindowDidChangeContentsHostedInLayerSurfaceNotification, 0x7fffb685e8e0, 0x6180000a4680, 1400
  • NSAntialiasThresholdChangedNotification, 0x7fffb685e8e0, 0x6080001e0300, 1400
  • kCFLocaleCurrentLocaleDidChangeNotification, 0x7fffb685e8e0, 0x7fffb685e9c0, 1001
  • some_string, 0x7fffb685e8e0, 0x600000000210, 1400
  • ...

Upvotes: 2

Duyen-Hoa
Duyen-Hoa

Reputation: 15784

I think it's possible with a "hacky" way: using Swizzling to observe the NSNotificationCenter.addObserver method.

@implementation NSNotificationCenter (Swizzling)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];

        SEL originalSelector = @selector(addObserver:selector:name:object:);
        SEL swizzledSelector = @selector(swizzling_addObserver:selector:name:object:);

        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

        BOOL didAddMethod =
        class_addMethod(class,
                        originalSelector,
                        method_getImplementation(swizzledMethod),
                        method_getTypeEncoding(swizzledMethod));

        if (didAddMethod) {
            class_replaceMethod(class,
                                swizzledSelector,
                                method_getImplementation(originalMethod),
                                method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

- (void)swizzling_addObserver:(id)observer selector:(SEL)aSelector name:(NSNotificationName)aName object:(id)anObject {
    //implement code here to store all notifications.

    //then call original method (read in the link below to understand why we call **swizzling_addObserver** but not **addObserver**
    [self swizzling_addObserver:observer selector:aSelector name:aName object:anObject];
}

To learn more about swizzling, you can read this post: http://nshipster.com/method-swizzling/

Upvotes: 0

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