Instance Method

addObserver(_:forKeyPath:options:context:)

Raises an exception.

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 set, 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

NSSet objects are not observable, so this method raises an exception when invoked on an NSSet object. Instead of observing a set, observe the unordered to-many relationship for which the set is the collection of related objects.