Why does UILabel.text result in “fatal error: unexpectedly found nil while unwrapping an Optional value”?

Question

I've read several answers to this question and have tried all recommendations with no success. I'm fairly new to swift and am building an app with Swift, PHP and MySQL. I'm receiving the error after the user has logged in to the app and the system should be displaying the username via a label using UILabel.text. The error is occurring on setting a value to the UILabel.text variable. My code is included below. I've tried to hardcode values on other pages and am getting this error throughout my project.

import UIKit

class HomeViewController: UITabBarController {

    @IBOutlet var usernameLbl: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        // set global variables
        let username = (user!["username"] as AnyObject).uppercased

        // label values
        print(usernameLbl ?? username!)
        usernameLbl.text = username
    }
}

I'm accessing the HomeViewController programmatically. The app uses a tab bar and the first page of it is Home. The code is from a course I'm taking on Udemy. Here is how I'm accessing Home:

// func to pass to home page or to tabBar
func login() {

    // refer to our Main.storyboard
    let storyboard = UIStoryboard(name: "Main", bundle: nil)

    // store our tabBar Object from Main.storyboard in tabBar var
    let tabBar = storyboard.instantiateViewController(withIdentifier: "tabBar")

    // present tabBar that is storing in tabBar var
    window?.rootViewController = tabBar

}

Answer 1

Seeing an @IBOutlet on a UITabBarController is very suspicious. You generally have a tab bar controller which presents child UIViewController subclasses, and put labels on those child view controllers, not the tab bar controller. A tab bar controller does not generally have IBOutlet references. The child view controllers would have them.

Double check to which class you've connected that @IBOutlet and confirm whether it's a subclass of UIViewController or UITabBarController.