Force unwrapping nil optional for UIImageView when transitioning to view controller - swift

Question

I'm running into an error when transitioning to view controllers by overriding the built-in prepare() function in Swift. I have a UIImageView for backgrounds on my screens. Here is the code for two of the view controllers in question.
import UIKit
import FirebaseAuth
class HomeVC: UIViewController {
#IBOutlet weak var signOutButton: UIButton!
#IBOutlet weak var backgroundImageView: UIImageView!
#IBOutlet weak var friendsNavButton: UIButton!
#IBOutlet weak var homeNavButton: UIButton!
#IBOutlet weak var profileNavButton: UIButton!
#IBOutlet weak var bumpButton: UIButton!
#IBOutlet weak var welcomeLabel: UILabel!
#IBOutlet weak var doNotDisturbLabel: UILabel!
#IBOutlet weak var doNotDisturbButton: UIButton!
var userName = ""
var dndIsOn: Bool = false
#IBAction func dndToggled(_ sender: Any) {
dndIsOn = !dndIsOn
User.current.available = !dndIsOn
FirestoreService.db.collection(Constants.Firestore.Collections.users).document(User.current.uid).updateData([Constants.Firestore.Keys.available : !dndIsOn])
if dndIsOn {
print("DND is on!")
setupDNDUI()
} else if !dndIsOn {
print("DND is off!")
setupActiveUI()
}
}
#IBAction func signOutTapped(_ sender: Any) {
let firAuth = Auth.auth()
do {
try firAuth.signOut()
} catch let signOutError as NSError {
print ("Error signing out: %#", signOutError)
}
print("Successfully signed out")
}
#IBAction func bumpTapped(_ sender: Any) {
self.performSegue(withIdentifier: Constants.Segues.toCall, sender: self)
}
#IBAction func friendsNavTapped(_ sender: Any) {
self.performSegue(withIdentifier: Constants.Segues.toFriends, sender: self)
}
#IBAction func profileNavTapped(_ sender: Any) {
let nav = self.navigationController //grab an instance of the current navigationController
DispatchQueue.main.async { //make sure all UI updates are on the main thread.
nav?.view.layer.add(CATransition().segueFromLeft(), forKey: nil)
nav?.pushViewController(ProfileVC(), animated: false)
}
}
override func viewDidLoad() {
super.viewDidLoad()
self.navigationController?.setNavigationBarHidden(true, animated: true)
self.backgroundImageView.contentMode = UIView.ContentMode.scaleAspectFill
doNotDisturbLabel.isHidden = true
if !userName.isEmpty {
welcomeLabel.text = "Welcome Back, " + userName + "!"
} else {
welcomeLabel.text = ""
}
}
override var preferredStatusBarStyle: UIStatusBarStyle {
return .darkContent
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
guard let friendsVC = segue.destination as? FriendsVC else {
return
}
FirestoreService.db.collection(Constants.Firestore.Collections.users).document(User.current.uid).getDocument { (snapshot, err) in
if let err = err {
print(err.localizedDescription)
} else {
let data = snapshot!.data()!
let requests = data[Constants.Firestore.Keys.requests] as? [String]
if let requests = requests {
friendsVC.requests = requests
}
}
}
}
class FriendsVC: UIViewController {
//var friends: [Friend] = User.current.friends
var friends: [User] = []
var requests: [String]?
#IBOutlet weak var requestsNumberLabel: UILabel!
#IBOutlet weak var backgroundImageView: UIImageView!
#IBOutlet weak var friendRequestsButton: UIButton!
#IBOutlet weak var homeNavButton: UIButton!
#IBOutlet weak var friendsTitle: UILabel!
#IBOutlet weak var friendTableView: UITableView!
#IBOutlet weak var addFriendButton: UIButton!
#IBOutlet weak var tableViewTopConstraint: NSLayoutConstraint!
#IBAction func friendRequestsTapped(_ sender: Any) {
self.performSegue(withIdentifier: Constants.Segues.toRequests, sender: self)
}
#IBAction func homeNavTapped(_ sender: Any) {
let nav = self.navigationController //grab an instance of the current navigationController
DispatchQueue.main.async { //make sure all UI updates are on the main thread.
nav?.view.layer.add(CATransition().segueFromLeft(), forKey: nil)
nav?.pushViewController(HomeVC(), animated: false)
}
}
override func viewDidLoad() {
super.viewDidLoad()
self.navigationController?.setNavigationBarHidden(true, animated: true)
backgroundImageView.contentMode = UIView.ContentMode.scaleAspectFill
friendTableView.backgroundView?.backgroundColor = .white
friendsTitle.isHidden = false
UserService.getUserArray(uids: User.current.friendUids, completion: { (users) in
guard let users = users else {
print("User has no friends")
return
}
self.friends = users
self.friendTableView.reloadData()
})
guard let requests = self.requests else {
friendRequestsButton.isHidden = true
requestsNumberLabel.isHidden = true
self.tableViewTopConstraint.constant = 0
return
}
requestsNumberLabel.text = requests.count.description
// Do any additional setup after loading the view.
friendTableView.delegate = self
friendTableView.dataSource = self
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let homeVC = segue.destination as? HomeVC {
homeVC.userName = User.current.firstName
} else if let requestsVC = segue.destination as? RequestsVC {
UserService.getUserArray(uids: self.requests!) { (requesters) in
if let requesters = requesters {
requestsVC.requesters = requesters
}
}
}
}
}
When my app loads into the home screen, there is no problem, and when a button is tapped to transition to FriendsVC, there is no problem. However, when I try to initiate the transition from HomeVC to ProfileVC or from FriendVC to HomeVC, I get the error: "Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value" at the self.backgroundImageView.contentMode = UIView.ContentMode.scaleAspectFill lines in my viewDidLoad methods. These segues have something in common in that these are the ones where I override the prepare() function, but I'm not sure what I'm doing wrong