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-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context Context is important if you ship your class for others to use.Context lets your class observer verify that its you observer which is being called. The ...

Most KVO and KVC functionality is already implemented by default on all NSObject subclasses. To start observing a property named firstName of an object named personObject do this in the observing class: [personObject addObserver:self forKeyPath:@"firstName" ...