As of Swift 2.2, there is a special syntax for compiler-time checked selectors. It uses the syntax: #selector(methodName).

Swift 3 and later:

var b = UIBarButtonItem(
title: "Continue",
style: .plain,
target: self,
action: #selector(sayHello(sender:))
)


func sayHello(sender: UIBarButtonItem) {
}

If you are unsure what the method name should look like, there is a special version of the copy command that is very helpful. Put your cursor somewhere in the base method name (e.g. sayHello) and press Shift+Control+Option+C. That puts the ‘Symbol Name’ on your keyboard to be pasted. If you also hold Command it will copy the ‘Qualified Symbol Name’ which will include the type as well.

Swift 2.3:

var b = UIBarButtonItem(
title: "Continue",
style: .Plain,
target: self,
action: #selector(sayHello(_:))
)


func sayHello(sender: UIBarButtonItem) {
}

This is because the first parameter name is not required in Swift 2.3 when making a method call.

You can learn more about the syntax on swift.org here: https://swift.org/blog/swift-2-2-new-features/#compile-time-checked-selectors

Swift 4/5 example

button.target = self
button.action = #selector(buttonClicked(sender:))


@objc func buttonClicked(sender: UIBarButtonItem) {
        

}

May this one help a little more

Let suppose if you want to make the bar button in a separate file(for modular approach) and want to give selector back to your viewcontroller, you can do like this :-

your Utility File

class GeneralUtility {


class func customeNavigationBar(viewController: UIViewController,title:String){
let add = UIBarButtonItem(title: "Play", style: .plain, target: viewController, action: #selector(SuperViewController.buttonClicked(sender:)));
viewController.navigationController?.navigationBar.topItem?.rightBarButtonItems = [add];
}
}

Then make a SuperviewController class and define the same function on it.

class SuperViewController: UIViewController {


override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
@objc func buttonClicked(sender: UIBarButtonItem) {


}
}

and In our base viewController(which inherit your SuperviewController class) override the same function

import UIKit


class HomeViewController: SuperViewController {


override func viewDidLoad() {
super.viewDidLoad()


// Do any additional setup after loading the view.
}


override func viewWillAppear(_ animated: Bool) {
GeneralUtility.customeNavigationBar(viewController: self,title:"Event");
}


@objc override func buttonClicked(sender: UIBarButtonItem) {
print("button clicked")
}
}

Now just inherit the SuperViewController in whichever class you want this barbutton.

Thanks for the read

Swift 5

if you have created UIBarButtonItem in Interface Builder and you connected outlet to item and want to bind selector programmatically.

Don't forget to set target and selector.

addAppointmentButton.action = #selector(moveToAddAppointment)
addAppointmentButton.target = self


@objc private func moveToAddAppointment() {
self.presenter.goToCreateNewAppointment()
}

Swift 5 & iOS 13+ Programmatic Example

1. You must mark your function with @objc, see below example!
2. No parenthesis following after the function name! Just use #selector(name).
3. private or public doesn't matter; you can use private.

Code Example

override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
    

let menuButtonImage = UIImage(systemName: "flame")
let menuButton = UIBarButtonItem(image: menuButtonImage, style: .plain, target: self, action: #selector(didTapMenuButton))
navigationItem.rightBarButtonItem = menuButton
}


@objc public func didTapMenuButton() {
print("Hello World")
}

If you don't want to use target/action using a #selector, you can use primaryAction since iOS 14:

// here you can set the title or a image for the UIBarButtonItem
let action = UIAction(title: "", image: UIImage(systemName: "list.dash")) { _ in
// handler
print("hello world")
}
        

let barButtonItem = UIBarButtonItem(title: nil,
image: nil,
primaryAction: action,
menu: nil)