Instance Method

addObserver:forKeyPath:options:context:

Registers the observer object to receive KVO notifications for the key path relative to the object receiving this message.

Declaration

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

Parameters

observer

The object to register for KVO notifications. The observer must implement the key-value observing method observeValueForKeyPath:ofObject:change:context:.

keyPath

The key path, relative to the object receiving this message, of the property to observe. This value must not be nil.

options

A combination of the NSKeyValueObservingOptions values that specifies what is included in observation notifications. For possible values, see NSKeyValueObservingOptions.

context

Arbitrary data that is passed to observer in observeValueForKeyPath:ofObject:change:context:.

Discussion

Neither the object receiving this message, nor observer, are retained. An object that calls this method must also eventually call either the removeObserver:forKeyPath: or removeObserver:forKeyPath:context: method to unregister the observer when participating in KVO.

See Also

Registering for Observation

- removeObserver:forKeyPath:

Stops the observer object from receiving change notifications for the property specified by the key path relative to the object receiving this message.

- removeObserver:forKeyPath:context:

Stops the observer object from receiving change notifications for the property specified by the key path relative to the object receiving this message, given the context.