Instance Method

willChangeValue(forKey:)

Informs the observed object that the value of a given property is about to change.

Declaration

func willChangeValue(forKey key: String)

Parameters

key

The name of the property that will change.

Discussion

Use this method when implementing key-value observer compliance manually to inform the observed object that the value at key is about to change.

The change type of this method is NSKeyValueChangeSetting.

Special Considerations

You rarely need to override this method in subclasses, but if you do, be sure to call super.

See Also

Notifying Observers of Changes

func didChangeValue(forKey: String)

Informs the observed object that the value of a given property has changed.

func willChange(NSKeyValueChange, valuesAt: IndexSet, forKey: String)

Informs the observed object that the specified change is about to be executed at given indexes for a specified ordered to-many relationship.

func didChange(NSKeyValueChange, valuesAt: IndexSet, forKey: String)

Informs the observed object that the specified change has occurred on the indexes for a specified ordered to-many relationship.

func willChangeValue(forKey: String, withSetMutation: NSKeyValueSetMutationKind, using: Set<AnyHashable>)

Informs the observed object that the specified change is about to be made to a specified unordered to-many relationship.

func didChangeValue(forKey: String, withSetMutation: NSKeyValueSetMutationKind, using: Set<AnyHashable>)

Informs the observed object that the specified change was made to a specified unordered to-many relationship.