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 array, of the property to observe. This value must not be
nil. - options:
A combination of Nskeyvalueobservingoptions values that specifies what is included in observation notifications.
- context:
Arbitrary data that is passed to
observerin Observevalue(forkeypath:of:change:context:).
Discussion
NSArray objects are not observable, so this method raises an exception when invoked on an NSArray object. Instead of observing an array, observe the to-many relationship for which the array is the collection of related objects.