Animate Auto Layout Constraints Swift 4

ViewController.swift

//
//  ViewController.swift
//  SwiftButton
//
//  Created by Paul Solt on 7/21/15.
//  Copyright (c) 2015 Paul Solt. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    var updateTimer: Timer?
    var startDate: Date!
    var buttonOn: Bool = false

    var button1: UIButton!
    var button2: UIButton!
    var bottomButtonConstraint: NSLayoutConstraint!

    @IBOutlet weak var bottomPanelConstraint: NSLayoutConstraint!

    
    // Storyboard connections
    @IBOutlet weak var timeLabel: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
     
        updateTimer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(updateTimer(timer:)), userInfo: nil, repeats: true)
    
        startDate = Date()
        
        setupButton()
//        button1.alpha = 0
        
        setupAnimateButton()
    }
    
    
    func setupButton() {
        
        button1 = UIButton(type: .system)
        
        button1.setTitle("Animate Auto Layout", for: .normal)
        
        button1.bounds = CGRect(x: 0, y: 0, width: 300, height: 80)
        button1.center = CGPoint(x: view.bounds.width / 2, y: 80 + 20 + 40 + 8 + 8) // 80 point button, 20 point status bar, 40 point half button, 8 point margins
        
        button1.setBackgroundImage(UIImage(named: "BlueButton"), for: .normal)
        
        button1.titleLabel?.font = UIFont.systemFont(ofSize: 17)
        button1.setTitleColor(.white, for: .normal)
        
        button1.addTarget(self, action: #selector(animateButtonPressed(sender:)), for: .touchUpInside)
        
        view.addSubview(button1)
        
    }
    
    func setupAnimateButton() {
        
        button2 = UIButton(type: .system)
        
        button2.setTitle("Auto Layout Slide", for: .normal)
        button2.setBackgroundImage(UIImage(named: "BlueButton"), for: .normal)
        
        button2.titleLabel?.font = UIFont.systemFont(ofSize:17)
        button2.setTitleColor(.white, for: .normal)
        
        view.addSubview(button2)
        
        // Auto Layout
        
        // Disable Auto Resizing constraints
        button2.translatesAutoresizingMaskIntoConstraints = false
        
        let margins = view.layoutMarginsGuide
        button2.leadingAnchor.constraint(equalTo: margins.leadingAnchor).isActive = true
        button2.trailingAnchor.constraint(equalTo: margins.trailingAnchor).isActive = true
        
        // Store a reference to the constraint to manage it
        bottomButtonConstraint = button2.topAnchor.constraint(equalTo: margins.bottomAnchor, constant: 0)
        bottomButtonConstraint.isActive = true
        
        // offscreen + invisible
//        button2.alpha = 0
        bottomButtonConstraint.constant = 0
    }
    
    func showButton() {
        
        UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 0.8, initialSpringVelocity: 15, options: [], animations: { () -> Void in
            
            self.button2.alpha = 1

            self.bottomButtonConstraint.constant = -100
            self.bottomPanelConstraint.constant = self.button2.frame.height + 20 + 8  // button height + bottom spacing + in-between spacing

            self.view.layoutIfNeeded()

            
        }, completion: nil)
        
    }
    
    func hideButton() {
        
        UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 1.0, initialSpringVelocity: 15, options: [], animations: { () -> Void in
            self.button2.alpha = 0

            self.bottomButtonConstraint.constant = 0 // 100
            self.bottomPanelConstraint.constant = 20

            self.view.layoutIfNeeded()


            }, completion: nil)

    }
    
    @IBAction func addButtonPressed(_ sender: Any) {
        print("add")

        UIView.animate(withDuration: 0.3, animations: { () -> Void in
            if self.button1.alpha == 0 {
                self.button1.alpha = 1 // show
            } else {
                self.button1.alpha = 0 // hide
            }
        })
        
        
    
    }
    
    @objc func animateButtonPressed(sender: AnyObject) {
        print("animate")
        
        if buttonOn {
            hideButton()
        } else {
            showButton()
        }
        
        buttonOn = !buttonOn
    }
    
    // MARK: Timer Logic
    
    @objc func updateTimer(timer: Timer) {

        let seconds = -startDate.timeIntervalSinceNow
        let dateComponentFormatter = DateComponentsFormatter()
        dateComponentFormatter.unitsStyle = .positional
        dateComponentFormatter.allowedUnits = [.minute, .second, .hour]
        dateComponentFormatter.zeroFormattingBehavior = .pad
        
        let timeString = dateComponentFormatter.string(from: seconds)
        
        timeLabel.text = timeString
    }
}