iOS KVO observe another class property

Question

Is there anyway observe another class propery, like observe an singleton instance in iOS. I have tried, but I don't know hot to write keypath from another class.

[self addObserver:self forKeyPath:@"otherclass/keypath" options:NSKeyValueObservingOptionNew context:NULL];

Answer 1

The receiver of the addObserver message is the observed object. So it should be the instance of your singleton. The keypath should start with the name of a observable property of this singleton. E.g.:

[[SingletonClass instance] addObserver:self forKeyPath:@"propertyName" options:NSKeyValueObservingOptionNew context:NULL];

A keypath can contain a chain of property names which are separated by dots. Just for illustration: If you want observe the root view controller of the key window, you can do

[[UIApplication sharedApplication] addObserver:self 
    forKeyPath:@"keyWindow.rootViewController" 
    options:NSKeyValueObservingOptionNew context:NULL];