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

func addObserver(_ observer: NSObject, forKeyPath keyPath: String, options: NSKeyValueObservingOptions = [], context: UnsafeMutableRawPointer?)

Parameters

observer

The object to register for KVO notifications. The observer must implement the key-value observing method observeValue(forKeyPath:of: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 observeValue(forKeyPath:of: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

Related Symbols

func removeObserver(NSObject, forKeyPath: String)

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