Google Sign-in crash & error: uiDelegate must either be a |UIViewController| - ios

Question

I'm trying to implement Google Sign-in to an iOS app but the app crashes on clicking on the Sign-in button with the following error:
reason: 'uiDelegate must either be a |UIViewController| or implement the |signIn:presentViewController:| and |signIn:dismissViewController:| methods from |GIDSignInUIDelegate|.'
I'm not sure where I'm going wrong. I've followed the sample code from Google's iOS github exactly. I also can't get Google's sample to compile. If anyone could point me in the right direction, that would be great. Most of the SO questions are based on dated code.
Viewcontroller
import UIKit
import GoogleSignIn
#objc(ViewController)
class ViewController: UIViewController, GIDSignInUIDelegate {
// Viewcontroller buttons
#IBOutlet weak var signInButton: GIDSignInButton!
#IBOutlet weak var signOutButton: UIButton!
#IBOutlet weak var disconnectButton: UIButton!
#IBOutlet weak var statusText: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
GIDSignIn.sharedInstance().uiDelegate = self
// Sign in automatically
GIDSignIn.sharedInstance().signInSilently()
// Something to do with notifications
NotificationCenter.default.addObserver(self,
selector: #selector(ViewController.receiveToggleAuthUINotification(_:)),
name: NSNotification.Name(rawValue: "ToggleAuthUINotification"),
object: nil)
statusText.text = "Initialized Swift App..."
toggleAuthUi()
}
// Sign out tapped
#IBAction func didTapDisconnect(_ sender: AnyObject) {
GIDSignIn.sharedInstance().disconnect()
statusText.text = "Disconnecting"
}
// Toggle auth
func toggleAuthUi() {
if GIDSignIn.sharedInstance().hasAuthInKeychain() {
signInButton.isHidden = true
signOutButton.isHidden = false
disconnectButton.isHidden = false
} else {
signInButton.isHidden = false
signOutButton.isHidden = true
disconnectButton.isHidden = true
}
}
override var preferredStatusBarStyle: UIStatusBarStyle {
return UIStatusBarStyle.lightContent
}
deinit {
NotificationCenter.default.removeObserver(self,
name: NSNotification.Name(rawValue: "ToggleAuthUINotification"),
object: nil)
}
#objc func receiveToggleAuthUINotification(_ notification: NSNotification) {
if notification.name.rawValue == "ToggleAuthUINotification" {
self.toggleAuthUi()
if notification.userInfo != nil {
guard let userInfo = notification.userInfo as? [String:String] else {return}
self.statusText.text = userInfo["statusText"]!
}
}
}
}
AppDelegate:
import UIKit
import GoogleSignIn
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, GIDSignInDelegate {
var window: UIWindow?
// Did Finished Launching
func application (_ application: UIApplication,
didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
// Init Sign in
GIDSignIn.sharedInstance().clientID = "XXXXXXXXX"
GIDSignIn.sharedInstance().delegate = self
return true
}
// Open URL
func application (_app: UIApplication, open url: URL, options: [UIApplicationOpenURLOptionsKey: Any]) -> Bool {
return GIDSignIn.sharedInstance().handle(url, sourceApplication: options[UIApplicationOpenURLOptionsKey.sourceApplication] as? String, annotation: options[UIApplicationOpenURLOptionsKey.annotation])
}
public func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {
if let error = error {
print("\(error.localizedDescription)")
NotificationCenter.default.post(
name: Notification.Name(rawValue: "ToggleAuthUINotificiation"), object: nil, userInfo: nil)
} else {
// User Stuff
let userID = user.userID
let idToken = user.authentication.idToken
let fullName = user.profile.name
let givenName = user.profile.givenName
let familyName = user.profile.familyName
let email = user.profile.email
NotificationCenter.default.post(
name: Notification.Name(rawValue: "ToggleAuthUINotification"),
object: nil,
userInfo: ["statusText": "Signed in user:\n\(fullName)"])
}
}
public func sign(_ signIn: GIDSignIn!, didDisconnectWith user: GIDGoogleUser!, withError error: Error!) {
// Disconnect the user
NotificationCenter.default.post(
name: Notification.Name(rawValue: "ToggleAuthUINotification"),
object: nil,
userInfo: ["statusText": "User has disconnect."])
}
}

Answer 1

tl;dr: If using a non-UIViewController as a uiDelegate - check if Xcode is warning you that "Instance method [...] nearly matches optional requirement [...]" and use the Fix-Its. Make sure your functions match the required signature exactly.
I had the same error after following the sample code.
In my case the setup was a bit different, so I am not sure if my solution is applicable to your question - but because this StackOverflow answer shows up in Google Search, I thought I'd provide my resolution here for any people stumbling upon it:
I needed a non-UIVIewController subclass to be the Google Sign In uiDelegate. As the documentation and the error state, this means you need to implement some methods. I had implemented them, so it was strange that things were crashing.
In my case, the issue was that the copy-pasted code from Google's documentation was not exactly matching the Swift function signatures. In fact, I had warnings in Xcode, saying "Instance method [...] nearly matches optional requirement [...]". I used the auto Fix-Its by Xcode (it was stuff such as Error instead of NSError, or _ before a function's argument.)
Then it all worked.