IOS Buttons Menu with image

ViewController.swift

class MenuViewController: UIViewController {
    var buttons: [UIButton] = []
    var imageView : UIImageView!
    var constraintLeft : NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        addMenuItems()
    }
    
    func addMenuItems() {
        
        for _ in 0...4 {
            let button : UIButton = UIButton()
            self.view.addSubview(button)
            button.backgroundColor = UIColor.darkGray
            button.addTarget(self, action: #selector(didSelectedButton(_:)), for: .touchUpInside)
            self.buttons.append(button)
            
        }
        
        for (index, button) in buttons.enumerated() {
            
            button.setTitle(" \(index)", for: .normal)
            if index == 0 {
                button.translatesAutoresizingMaskIntoConstraints = false
                button.leftAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.leftAnchor, constant: 0).isActive = true
                button.widthAnchor.constraint(greaterThanOrEqualToConstant: 1).isActive = true
                button.heightAnchor.constraint(equalToConstant: 50).isActive = true
                button.topAnchor.constraint(equalTo: self.view.topAnchor, constant:200).isActive = true
                
                self.imageView = UIImageView()
                self.view.addSubview(self.imageView)
                self.imageView.backgroundColor = UIColor.red
                
                self.imageView.translatesAutoresizingMaskIntoConstraints = false
               constraintLeft =  self.imageView.leftAnchor.constraint(equalTo: button.leftAnchor, constant: 0)
                constraintLeft.isActive = true
                
                self.imageView.widthAnchor.constraint(equalTo: button.widthAnchor, multiplier: 1).isActive = true
                self.imageView.heightAnchor.constraint(equalToConstant: 4).isActive = true
                self.imageView.topAnchor.constraint(equalTo: self.view.topAnchor, constant:250).isActive = true
                
            }
            else {
                
                let preButton = buttons[index - 1]
                button.translatesAutoresizingMaskIntoConstraints = false
                button.leftAnchor.constraint(equalTo: preButton.rightAnchor, constant: 0).isActive = true
                button.widthAnchor.constraint(equalTo: preButton.widthAnchor, multiplier: 1).isActive = true
                button.heightAnchor.constraint(equalToConstant: 50).isActive = true
                button.topAnchor.constraint(equalTo: self.view.topAnchor, constant:200).isActive = true
                if index == self.buttons.count - 1 {
                    button.rightAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.rightAnchor, constant: 0).isActive = true
                }
            }
            
        }
        
    }
    
    @objc func didSelectedButton(_ button:UIButton) {

        UIView.animate(withDuration: 0.5, delay: 0.1, usingSpringWithDamping: 0.85, initialSpringVelocity: 1, options: .curveEaseInOut, animations: {
            self.constraintLeft.isActive = false
            self.constraintLeft =  self.imageView.leftAnchor.constraint(equalTo: button.leftAnchor, constant: 0)
            self.constraintLeft.isActive = true
            self.view.layoutIfNeeded()
        }, completion:nil)
    }

}