Custom Google Sign-In button - iOS

Swift 3 Version

In Swift make sure you have added briding header as the library is written in objective C.

1. Add your own button into storyBoard

2. drag action into viewController

   @IBAction func googlePlusButtonTouchUpInside(sender: AnyObject) {
         GIDSignIn.sharedInstance().signIn()
   } 
   

3. handle delegate methods

   //MARK:Google SignIn Delegate
    func signInWillDispatch(signIn: GIDSignIn!, error: NSError!) {
     // myActivityIndicator.stopAnimating()
       }
   
   // Present a view that prompts the user to sign in with Google
      func sign(_ signIn: GIDSignIn!,
                 present viewController: UIViewController!) {
           self.present(viewController, animated: true, completion: nil)
       }
   
   // Dismiss the "Sign in with Google" view
    func sign(_ signIn: GIDSignIn!,
                 dismiss viewController: UIViewController!) {
           self.dismiss(animated: true, completion: nil)
       }
   
   //completed sign In    
   public func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error!) {
   
           if (error == nil) {
         // Perform any operations on signed in user here.
               let userId = user.userID                  // For client-side use only!
              let idToken = user.authentication.idToken // Safe to send to the server
               let fullName = user.profile.name
              let givenName = user.profile.givenName
              let familyName = user.profile.familyName
              let email = user.profile.email
             // ...
           } else {
               print("\(error.localizedDescription)")
           }
       }
   

You can add your own button instead of using Google Sign-In button Do follwing things

Objective C Version

1)Add your own button into storyBoard

2)drag action into viewController

- (IBAction)googlePlusButtonTouchUpInside:(id)sender {
     [GIDSignIn sharedInstance].delegate = self;
     [GIDSignIn sharedInstance].uiDelegate = self;
     [[GIDSignIn sharedInstance] signIn];
  }

3)handle delegate methods

#pragma mark - Google SignIn Delegate

- (void)signInWillDispatch:(GIDSignIn *)signIn error:(NSError *)error {

  }

// Present a view that prompts the user to sign in with Google

- (void)signIn:(GIDSignIn *)signIn presentViewController:(UIViewController *)viewController
{
    [self presentViewController:viewController animated:YES completion:nil];
}

// Dismiss the "Sign in with Google" view

- (void)signIn:(GIDSignIn *)signIn dismissViewController:(UIViewController *)viewController {
    [self dismissViewControllerAnimated:YES completion:nil];

}

//completed sign In

- (void)signIn:(GIDSignIn *)signIn didSignInForUser:(GIDGoogleUser *)user
     withError:(NSError *)error {
//user signed in
//get user data in "user" (GIDGoogleUser object)
}

Swift 4 Version

In Swift make sure you have added briding header as the library is written in objective C

1)Add your own button into storyBoard

2)drag action into viewController

@IBAction func googlePlusButtonTouchUpInside(sender: AnyObject) {
      GIDSignIn.sharedInstance().delegate=self
      GIDSignIn.sharedInstance().uiDelegate=self
      GIDSignIn.sharedInstance().signIn()
} 

3)handle delegate methods

//MARK:Google SignIn Delegate

func signInWillDispatch(_ signIn: GIDSignIn!, error: Error!) {
}

// Present a view that prompts the user to sign in with Google

func signIn(_ signIn: GIDSignIn!,
    presentViewController viewController: UIViewController!) {
  self.present(viewController, animated: true, completion: nil)
}

// Dismiss the "Sign in with Google" view

func signIn(_ signIn: GIDSignIn!,
    dismissViewController viewController: UIViewController!) {
  self.dismiss(animated: true, completion: nil)
}

//completed sign In

   public func signIn(_ signIn: GIDSignIn!, didSignInForUser user: GIDGoogleUser!,
      withError error: Error!) {
        if (error == nil) {
          // Perform any operations on signed in user here.
          let userId = user.userID                  // For client-side use only!
          let idToken = user.authentication.idToken // Safe to send to the server
          let fullName = user.profile.name
          let givenName = user.profile.givenName
          let familyName = user.profile.familyName
          let email = user.profile.email
          // ...
        } else {
          print("\(error.localized)")
        }
    }

Edit: Here is the reference/evidence for usage of custom button, Google Doc reference

In these examples, the view controller is a subclass of UIViewController. If, in your project, the class that implements GIDSignInUIDelegate is not a subclass of UIViewController, implement the signInWillDispatch:error:, signIn:presentViewController:, and signIn:dismissViewController: methods of the GIDSignInUIDelegate protocol. Also don't forget to set UI delegate GIDSignIn.sharedInstance()?.uiDelegate = self