Informs the observed object that the value of a given property is about to change.
SDKs
- iOS 2.0+
- macOS 10.3+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
Framework
- Foundation
Declaration
- (void)willChangeValueForKey:(NSString *)key;
Parameters
keyThe 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 NSKey.
Special Considerations
You rarely need to override this method in subclasses, but if you do, be sure to call super.