Add animation to UILabel when the page is opened

I read and watched many tutorial about adding animation to labels but none of them work for me as I wanted. I want when I open a view controller, after a second, a UILabel start to fade in from the bottom of the page and come to the center of the page. for example here is the outlet of the label that I said about

  @IBOutlet weak var welcomeLabel: UILablel!

I made this function and add it to the viewdidload but it's not showing any animation, also when I tap on it will crash with this error:

Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value

here is the function:

func addAnimation() {
    UILabel.animate(withDuration: 3, delay: 3, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: .curveEaseOut, animations: {
        self.welcomeLabel.transform = CGAffineTransform(translationX: 0, y: -200)
    })
}

I also know this is not the animation that I wated, I just add it for the test. Could you help me to write the right animation that I wanted:

Start to fade in and move from the bottom to the center of the page.

thank you so much

Solution

Create @IBOutlet of UILabel and put the label in the center of the screen and add the required constraint.

Create @IBOutlet of label center Y alignment of Constraint like below.

    @IBOutlet weak var centerY: NSLayoutConstraint!

Then change its constant value.

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        centerY.constant =  self.view.bounds.height/2
        self.view.layoutIfNeeded()
        addAnimation()
    }

    func addAnimation(){
        UIView.animate(withDuration: 1, delay: 0, options: [.curveEaseOut], animations: {
            self.centerY.constant = 0
            self.welcomeLabel.alpha = 1.0
            self.view.layoutIfNeeded()
        }, completion: nil)

    }