Check out example codes for "swift move textfield when keyboard appears". It will help you in understanding the concepts better.

Code Example 1

class MyViewController: UIViewController {

// This constraint ties an element at zero points from the bottom layout guide
@IBOutlet var keyboardHeightLayoutConstraint: NSLayoutConstraint?

override func viewDidLoad() {
    super.viewDidLoad()
    // Note that SO highlighting makes the new selector syntax (#selector()) look
    // like a comment but it isn't one
    NotificationCenter.default.addObserver(self,
        selector: #selector(self.keyboardNotification(notification:)),
        name: UIResponder.keyboardWillChangeFrameNotification,
        object: nil)
}

deinit {
    NotificationCenter.default.removeObserver(self)
}

@objc func keyboardNotification(notification: NSNotification) {
    if let userInfo = notification.userInfo {
        let endFrame = (userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue
        let endFrameY = endFrame?.origin.y ?? 0
        let duration:TimeInterval = (userInfo[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber)?.doubleValue ?? 0
        let animationCurveRawNSN = userInfo[UIResponder.keyboardAnimationCurveUserInfoKey] as? NSNumber
        let animationCurveRaw = animationCurveRawNSN?.uintValue ?? UIView.AnimationOptions.curveEaseInOut.rawValue
        let animationCurve:UIView.AnimationOptions = UIView.AnimationOptions(rawValue: animationCurveRaw)
        if endFrameY >= UIScreen.main.bounds.size.height {
            self.keyboardHeightLayoutConstraint?.constant = 0.0
        } else {
            self.keyboardHeightLayoutConstraint?.constant = endFrame?.size.height ?? 0.0
        }
        UIView.animate(withDuration: duration,
                                   delay: TimeInterval(0),
                                   options: animationCurve,
                                   animations: { self.view.layoutIfNeeded() },
                                   completion: nil)
    }
}

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