---
title: Using Objective-C Runtime Features in Swift
framework: swift
role: article
role_heading: Article
path: swift/using-objective-c-runtime-features-in-swift
---

# Using Objective-C Runtime Features in Swift

Use selectors and key paths to interact with dynamic Objective-C APIs.

## Overview

Overview Some Objective-C APIs—like target-action—accept method or property names as parameters, then use those names to dynamically call or access the methods or properties. In Swift, you use the #selector and #keyPath expressions to represent those method or property names as selectors or key paths, respectively. Use Selectors to Arrange Calls to Objective-C Methods In Objective-C, a selector is a type that refers to the name of an Objective-C method. In Swift, Objective-C selectors are represented by the Selector structure, and you create them using the #selector expression. In Swift, you create a selector for an Objective-C method by placing the name of the method within the #selector expression: #selector(MyViewController.tappedButton(_:)). To construct a selector for a property’s Objective-C getter or setter method, prefix the property name using the getter: or setter: label, like #selector(getter: MyViewController.myButton). The example below shows a selector being used as part of the target-action pattern to call a method in response to the touchUpInside event. import UIKit class MyViewController: UIViewController {     let myButton = UIButton(frame: CGRect(x: 0, y: 0, width: 100, height: 50))

override init(nibName nibNameOrNil: NSNib.Name?, bundle nibBundleOrNil: Bundle?) {         super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)         let action = #selector(MyViewController.tappedButton)         myButton.addTarget(self, action: action, forControlEvents: .touchUpInside)     }

@objc func tappedButton(_ sender: UIButton?) {         print("tapped button")     }

required init?(coder: NSCoder) {         super.init(coder: coder)     } } If you need to disambiguate between overloaded functions, use parenthesized expressions along with the as operator to make the #selector expression refer unambiguously to a specific overload. Use Key Paths to Dynamically Access Objective-C Properties In Objective-C, a key is a string that identifies a specific property of an object. A key path is a string of dot-separated keys that specifies a sequence of object properties to traverse. Keys and key paths are frequently used for key-value coding (KVC), a mechanism for indirectly accessing an object’s attributes and relationships using string identifiers. important: Objective-C key paths are distinct from, but related to, key-path expressions in Swift. For information about key-path expressions, see Key-Path Expression in The Swift Programming Language. You use the #keyPath string expression to create compiler-checked keys and key paths that can be used by KVC methods like value(forKey:) and value(forKeyPath:). The #keyPath string expression accepts chained method or property references. It also supports chaining through optional values within a chain, such as #keyPath(Person.bestFriend.name). Key paths created using the #keyPath string expression don’t pass type information about the properties or methods they reference to the APIs that accept key paths. The example below defines a Person class, creates two instances of it, and uses several #keyPath string expressions to access properties and properties of those properties: class Person: NSObject {     @objc var name: String     @objc var friends: [Person] = []     @objc var bestFriend: Person? = nil

init(name: String) {         self.name = name     } }

let gabrielle = Person(name: "Gabrielle") let jim = Person(name: "Jim") let yuanyuan = Person(name: "Yuanyuan") gabrielle.friends = [jim, yuanyuan] gabrielle.bestFriend = yuanyuan

#keyPath(Person.name) // "name" gabrielle.value(forKey: #keyPath(Person.name)) // "Gabrielle" #keyPath(Person.bestFriend.name) // "bestFriend.name" gabrielle.value(forKeyPath: #keyPath(Person.bestFriend.name)) // "Yuanyuan" #keyPath(Person.friends.name) // "friends.name" gabrielle.value(forKeyPath: #keyPath(Person.friends.name)) // ["Yuanyuan", "Jim"]

## See Also

### Language Interoperability with Objective-C and C

- [Objective-C and C Code Customization](swift/objective-c-and-c-code-customization.md)
- [Migrating Your Objective-C Code to Swift](swift/migrating-your-objective-c-code-to-swift.md)
- [Cocoa Design Patterns](swift/cocoa-design-patterns.md)
- [Handling Dynamically Typed Methods and Objects in Swift](swift/handling-dynamically-typed-methods-and-objects-in-swift.md)
- [Imported C and Objective-C APIs](swift/imported-c-and-objective-c-apis.md)
- [Calling Objective-C APIs Asynchronously](swift/calling-objective-c-apis-asynchronously.md)