When is watchValueForKeyPath called?

Question

Does it get called after a property change (which means that the property setting tool is already popped out of the call stack) or when the property installer is running?

Swift is very convenient "Property observers". Does Obj-C have something similar for KVO?

Answer 1

It depends on what options were used when adding an observer. If the observer was added using NSKeyValueObservingOptionPrior, then it -observeValueForKeyPath:...is called both before and after the property change. Or, more precisely, it was called both during -willChange...and during the methods -didChange....

NSKeyValueObservingOptionPrior , -observeValueForKeyPath:... . ( -didChange....)

Swift KVO. , ( ) - / , ( ).

, KVO , . , - , .

Answer 2

https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Protocols/NSKeyValueObserving_Protocol/#//apple_ref/occ/instm/NSObject/observeValueForKeyPath:ofObject:change:context:

, . docs