KVOs and context

[oskaroskar]

Hello everyone!

I have trouble understanding why the context-parameter in the following method is needed.

- (void)addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context 

Specifically, I don’t understand the following paragraph in the book:

The most common use of this is to answer “Is this really the notification that I asked for?” For example, your superclass may use KVO. If you override observeValueForKeyPath:ofObject:change:context:, how do you know which notifications should be forwarded on to the superclass’s implementation?

What’s an example of “a superclass using KVO”?