Here is a technique to fire an alert in Swift 4.  

import UIKit


class ViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    @IBAction func setAlert(_ sender: UIButton) {
        // create the alert
        let alert = UIAlertController(title: “Hello”, message: “This is an Alert”, preferredStyle: .alert)
        // create the actions
        let okAction = UIAlertAction(title: “OK”, style: .default, handler: nil)
        let okActionNext = UIAlertAction(title: “Next”, style: .default, handler: nil)
        // create an action with a function
        let okActionThree = UIAlertAction(title: “Next”, style: .default, handler: { action in self.runThis()
        })
        // add the actions to the alert
        alert.addAction(okAction)
        alert.addAction(okActionNext)
        alert.addAction(okActionThree)
        // fire the alert
        present(alert, animated: true, completion: nil)
    }
    func runThis(){
        print (“WaHoo”)
   

}   
}