light(basic).swift

class ViewController: UIViewController {
    
    let colors = [UIColor.black, UIColor.blue]
    var index = 0
    
    
    @IBOutlet weak var btnView: UIButton!
    @IBAction func btn(_ sender: Any){

        btnView.backgroundColor = colors[index]
        update()
        
        if index == colors.count
        {
            index = 0
        }
    }
    
    func update()
    {
        
        index = index + 1
        
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
         btnView.backgroundColor = .blue  //進入畫面就顯示藍色
        
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}