How Can I Add a Background Image for FirebaseUI Login for iOS?

Question

I'd like to be able to place a background image behind the three sign-in buttons (for Google, Facebook, and Email) of the FirebaseUI login screen. FirebaseUI login is a drop-in authentication solution for iOS, Android, and Web. I'm having trouble with iOS.

There's a little bit of advice on Github, but not enough.

I first initialize my var customAuthPickerViewController : FIRAuthPickerViewController! near the top of the ViewController.swift file.

Then, this is the function in my ViewController.swift file, but it's not working. When I click the logout button, the app crashes, and no background image is ever shown.

// Customize the sign-in screen to have the Bizzy Books icon/background image

func authPickerViewController(for authUI: FIRAuthUI) -> FIRAuthPickerViewController {

    customAuthPickerViewController = authPickerViewController(for: authUI)
    backgroundImage = UIImageView(image: UIImage(named: "bizzybooksbee"))
    backgroundImage.contentMode = UIViewContentMode.scaleAspectFill
    customAuthPickerViewController.view.addSubview(backgroundImage)

    return customAuthPickerViewController
}

The background image "bizzybooksbee" is a Universal Image Set with 1x, 2x, and 3x images already loaded in my Assets.xcassets folder.

Here's a picture of what the login screen looks like without trying to implement the background image.

UPDATE: I'm able to get the image to show, with the code I gave in the comments below, but it shows OVER the sign-in buttons, as in the pic below.

Here's an image of the "heirarchy," with Jeffrey's help:

Answer 1

Here's the solution!

Remove the junk that doesn't work from ViewController.swift:

func authPickerViewController(for authUI: FIRAuthUI) -> FIRAuthPickerViewController {

    customAuthPickerViewController = authPickerViewController(for: authUI)
    backgroundImage = UIImageView(image: UIImage(named: "bizzybooksbee"))
    backgroundImage.contentMode = UIViewContentMode.scaleAspectFill
    customAuthPickerViewController.view.addSubview(backgroundImage)

    return customAuthPickerViewController   
}

Create a .swift "subclass" of FIRAuthPickerViewController that you can name anything, and add your background image/customization there:

import UIKit
import FirebaseAuthUI

class BizzyAuthViewController: FIRAuthPickerViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

        let width = UIScreen.main.bounds.size.width
        let height = UIScreen.main.bounds.size.height

        let imageViewBackground = UIImageView(frame: CGRect(x: 0, y: 0, width: width, height: height))
        imageViewBackground.image = UIImage(named: "bizzybooksbee")

        // you can change the content mode:
        imageViewBackground.contentMode = UIViewContentMode.scaleAspectFill

        view.insertSubview(imageViewBackground, at: 0)
    }}

In your ViewController.swift (or whatever you call it), in the section where you login, change authViewController to equal your new subclass, add a line for the navigation controller, and pass it into the self.present:

let authViewController = BizzyAuthViewController(authUI: authUI!)

let navc = UINavigationController(rootViewController: authViewController)

self.present(navc, animated: true, completion: nil)

I also made a YouTube tutorial which shows how to do this in depth.