我的按钮的 addTarget 中的操作不起作用

Question

Xcode did not report errors but nothing was printed when I pressed the button. I tried it with action:

#selector (print), action: #selector (self.print), action: #selector (ViewController.print)..etc..

Swift 4, Xcode 10.1

class SomeViewController:UIViewController {
var button:UIButton = UIButton()
func setupButton()
{
    button = UIButton(frame: CGRect(x: 140, y: 140, width: 90, height: 40))
    button.addTarget(self, action: #selector(print(-:)) , for: .touchUpOutside)
    navigationController?.navigationBar.addSubview(button)
    button.setTitle("Convert", for: .normal)
    button.backgroundColor = .yellow
    view.addSubview(button)


}

@objc func print(_sender: UIButton)
{
    print("Stackoverflow")
}

override func viewDidLoad() 
{
    super.viewDidLoad()
    view.addSubview(CollectionView)
    CollectionView.frame = view.frame
    setupButton()
 }
}

Answer 1

Change this ( You need touchUpInside instead of touchUpOutside )

button.addTarget(self, action: #selector(print(_:)) , for: .touchUpOutside)

to

button.addTarget(self, action: #selector(printRes) , for: .touchUpInside)

@objc func printRes(_ sender: UIButton) { }

Also don't use print as button action name because it's a reserved method

---

Also to get the button click action set it's type

button = UIButton(type: .system)
button.frame  = CGRect(x: 140, y: 140, width: 90, height: 40)

Answer 2

You just have to change event type from .touchUpOutside to .touchUpInside

Here isevents documentation