Detecting clicks on a button in Swift

Question

How can I detect clicks on the following UIKit element in Swift, in an Xcode 6 playground?

let testLabel = UILabel(frame: CGRectMake(0, 0, 120, 40))
testLabel.text = "My Button"

Answer 1

With Swift 3, UIButton - as a subclass of UIControl - has a method called addTarget(_:action:for:). addTarget(_:action:for:) has the following declaration:

func addTarget(_ target: Any?, action: Selector, for controlEvents: UIControlEvents)

Associates a target object and action method with the control.

---

The Playground code below shows how to detect a click on a button:

import PlaygroundSupport
import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .white

        // Create button
        let button = UIButton(type: UIButtonType.system)
        button.setTitle("Click here", for: UIControlState.normal)

        // Add action to button
        button.addTarget(self, action: #selector(buttonTapped(sender:)), for: UIControlEvents.touchUpInside)

        // Add button to controller's view
        view.addSubview(button)

        // Set Auto layout constraints for button
        button.translatesAutoresizingMaskIntoConstraints = false
        let horizontalConstraint = button.centerXAnchor.constraint(equalTo: view.centerXAnchor)
        let verticalConstraint = button.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint])
    }

    // trigger action when button is touched up
    func buttonTapped(sender: UIButton) {
        print("Button was tapped")
    }

}

// Display controller in Playground's timeline
let vc = ViewController()
PlaygroundPage.current.liveView = vc