import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var button: AnimationButton!{
        didSet{
            button.addTarget(self, action: #selector(buttonTapped(_:)), for: .primaryActionTriggered)
            button.backgroundColor = .gray
        }
    }

    @IBOutlet weak var buttonHeightConstraint: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    @IBAction func buttonTapped(_ sender: AnimationButton) {
        UIView.animate(withDuration: 3.0, animations: {
            self.updateConstraint()
        })
    }

    private func updateConstraint(){
        buttonHeightConstraint.constant =  button.hiddenSwitch.isSelected ? button.bounds.height + 100 : 50
        view.layoutIfNeeded()
    }
}

import UIKit

class AnimationButton: UIControl {

    @IBOutlet weak var hiddenSwitch: UIButton!{
        didSet{
            hiddenSwitch.setTitle("View Hidden Switch", for: .normal)
            hiddenSwitch.titleLabel?.font = UIFont.systemFont(ofSize: 18.0)
            hiddenSwitch.titleLabel?.adjustsFontSizeToFitWidth = true
        }
    }

    @IBOutlet weak var descritpionLabel: UILabel!

    public override init(frame: CGRect) {
        super.init(frame: frame)
        xibInit()
    }

    required public init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        xibInit()
    }

    private func xibInit(){
        guard let view = UINib(nibName: String(describing: type(of: self)), bundle: nil).instantiate(withOwner: self, options: nil).first as? UIView else{
            return
        }
        self.addSubview(view)
        self.translatesAutoresizingMaskIntoConstraints = false
        let constraints:[NSLayoutConstraint] = [
            self.topAnchor.constraint(equalTo: view.topAnchor),
            self.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            self.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            self.trailingAnchor.constraint(equalTo: view.trailingAnchor)
        ]
        NSLayoutConstraint.activate(constraints)

        descritpionLabel.alpha = 0.0
    }

    @IBAction func buttonTouchUpInside(_ sender: UIButton) {
        hiddenSwitch.isSelected = !hiddenSwitch.isSelected
        hiddenSwitch.layoutIfNeeded()

        UIView.animate(withDuration: 3.0, animations: {
            if self.hiddenSwitch.isSelected{
                self.descritpionLabel.alpha = 1.0
            }else{
                self.descritpionLabel.alpha = 0.0
            }
        })
        sendActions(for: .primaryActionTriggered)
    }
}