初始UIKit之alert

import UIKit

class ViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
    }
    
    @IBOutlet weak var myLabel: UILabel!
    
    @IBAction func click(_ sender: Any) {
        
        let alert = UIAlertController(title: "警告", message: "按钮被点击了", preferredStyle: .alert)
        
        alert.addAction(UIAlertAction(title: "知道啦", style: .default,handler: nil))
        
        self.present(alert, animated: true,completion: nil)
        
        myLabel.text = "IOS" + String(arc4random_uniform(10))
        
    }
}