How do I use KeyValueObserving (KVO) from Swift?

Key-Value Observing (KVO) is a mechanism provided by Cocoa to observe changes in properties of objects. In Swift, KVO can be used to monitor changes to properties of NSObject subclasses, enabling you to respond to changes dynamically.

Example of Key-Value Observing in Swift

In this example, we will create a simple class with a property that we can observe for changes.

import Foundation class Person: NSObject { @objc dynamic var name: String init(name: String) { self.name = name } } class Observer: NSObject { var observation: NSKeyValueObservation? func observePerson(person: Person) { observation = person.observe(\.name, options: [.old, .new]) { (person, change) in print("Name changed from \(change.oldValue ?? "nil") to \(change.newValue ?? "nil")") } } deinit { observation?.invalidate() } } let john = Person(name: "John") let observer = Observer() observer.observePerson(person: john) john.name = "John Doe" // This will trigger the observation and print the change

Key-Value Observing KVO Swift NSObject Property Observation Dynamic Properties

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