How do we know what methods get called?

[chanyeechoong]

In the book we set BNRObserver as an observer for lastTime property

__unused BNRObserver *observer = [[BNRObserver alloc] init]; // I want to know the new value and the old value whenever lastTime is changed [logger addObserver:observer forKeyPath:@"lastTime" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

in BNRObserver.m file we implemented this as the book says this method will get called

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { NSString *oldValue = [change objectForKey:NSKeyValueChangeOldKey]; NSString *newValue = [change objectForKey:NSKeyValueChangeNewKey]; NSLog(@"Observed: %@ of %@ was changed from %@ to %@", keyPath, object, oldValue, newValue); }

But how do we know that this method will be called at the first place ? can someone please explain?

[cvu123]

Had the same question. But I believe I found my answer here

When the value of an observed property of an object changes, the observer receives an observeValueForKeyPath:ofObject:change:context: message. All observers must implement this method.

Found this from Apple Docs developer.apple.com/library/ios … asics.html