View controller implementation for Google sign-in integration

Google-Sign-In-Integration-11.swift

import UIKit
import GoogleSignIn

class ViewController: UIViewController {
    
    var signInButton: UIButton!
    var signOutButton: UIButton!
    var greetingLabel: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()

        // Add greeting label
        greetingLabel = UILabel()
        greetingLabel.text = "Please sign in... 🙂"
        greetingLabel.textAlignment = .center
        greetingLabel.backgroundColor = .tertiarySystemFill
        view.addSubview(greetingLabel)
        greetingLabel.translatesAutoresizingMaskIntoConstraints = false
        greetingLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        greetingLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: -80).isActive = true
        greetingLabel.heightAnchor.constraint(equalToConstant: 54).isActive = true
        greetingLabel.widthAnchor.constraint(equalToConstant: 300).isActive = true
        
        // Add sign in button
        signInButton = UIButton()
        signInButton.layer.cornerRadius = 10.0
        signInButton.setTitle("Sign in with Google", for: .normal)
        signInButton.setTitleColor(.white, for: .normal)
        signInButton.backgroundColor = .systemRed
        signInButton.addTarget(self, action: #selector(signInButtonTapped(_:)), for: .touchUpInside)
        view.addSubview(signInButton)
        signInButton.translatesAutoresizingMaskIntoConstraints = false
        signInButton.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        signInButton.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
        signInButton.heightAnchor.constraint(equalToConstant: 44).isActive = true
        signInButton.widthAnchor.constraint(equalToConstant: 250).isActive = true
        
        // Add sign out button
        signOutButton = UIButton()
        signOutButton.layer.cornerRadius = 10.0
        signOutButton.setTitle("Sign Out 👋", for: .normal)
        signOutButton.setTitleColor(.label, for: .normal)
        signOutButton.backgroundColor = .systemFill
        signOutButton.addTarget(self, action: #selector(signOutButtonTapped(_:)), for: .touchUpInside)
        view.addSubview(signOutButton)
        signOutButton.translatesAutoresizingMaskIntoConstraints = false
        signOutButton.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        signOutButton.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 80).isActive = true
        signOutButton.heightAnchor.constraint(equalToConstant: 44).isActive = true
        signOutButton.widthAnchor.constraint(equalToConstant: 150).isActive = true
        
        // Sign out button is hidden by default
        signOutButton.isHidden = true
        
        // Let GIDSignIn know that this view controller is presenter of the sign-in sheet
        GIDSignIn.sharedInstance()?.presentingViewController = self
        
        // Register notification to update screen after user successfully signed in
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(userDidSignInGoogle(_:)),
                                               name: .signInGoogleCompleted,
                                               object: nil)
        
        // Update screen base on sign-in/sign-out status (when screen is shown)
        updateScreen()
    }
    
    private func updateScreen() {
        
        if let user = GIDSignIn.sharedInstance()?.currentUser {
            // User signed in
            
            // Show greeting message
            greetingLabel.text = "Hello \(user.profile.givenName!)! ✌️"
            
            // Hide sign in button
            signInButton.isHidden = true
            
            // Show sign out button
            signOutButton.isHidden = false
            
        } else {
            // User signed out
            
            // Show sign in message
             greetingLabel.text = "Please sign in... 🙂"
             
             // Show sign in button
             signInButton.isHidden = false
             
             // Hide sign out button
             signOutButton.isHidden = true
        }
    }
    
    // MARK:- Button action
    @objc func signInButtonTapped(_ sender: UIButton) {
        GIDSignIn.sharedInstance()?.signIn()
    }

    @objc func signOutButtonTapped(_ sender: UIButton) {
        GIDSignIn.sharedInstance()?.signOut()
        
        // Update screen after user successfully signed out
        updateScreen()
    }

    // MARK:- Notification
    @objc private func userDidSignInGoogle(_ notification: Notification) {
        // Update screen after user successfully signed in
        updateScreen()
    }
}