HelloWorld.swift

import UIKit

class ViewController: UIViewController {
    var label:UILabel? = nil

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        setupHardCodeLabel()
        setupHardCodeButton()
    }
    
    func setupHardCodeLabel() {
        let rect = CGRect(x: 100, y: 200, width: 300, height: 45)
        let label = UILabel(frame: rect)
        label.text = "Hello World!!!!!!!"
        self.label = label

        self.view.addSubview(label)
    }
    
    func setupHardCodeButton() {
        let rect = CGRect(x: 100, y: 300, width: 300, height: 45)
        let button = UIButton(frame: rect)
        button.setTitle("Click", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        button.addTarget(self, action: #selector(actionButtonClick), for: .touchUpInside)

        self.view.addSubview(button)
    }
    
    @objc func actionButtonClick(button:UIButton) {
        self.label?.text = "Action the button event!!"
    }
}