添加UINavigation时，“在展开可选值时意外发现nil”

Question

I was making this app (Swift 4) and it worked just fine.
But then , I added another page which was supposed work as the Main Menu(when you open the app , you see that) so therefore , I made another class which was a UINavigationController class(It wasn't the View Controller) but when I use a UIImage , I get "Unexpectedly found nil while unwrapping an Optional value".
My code :

import Foundation
import UIKit
class MainNavigation: UIVewController {
    // Screen width.
    public var screenWidth1: CGFloat {
        return UIScreen.main.bounds.width
    }

    // Screen height.
    public var screenHeight1: CGFloat {
        return UIScreen.main.bounds.height
    }


    @IBOutlet weak var backGround: UIImageView!
    @IBOutlet weak var playButton: UIButton!
    @IBOutlet weak var logo: UIImageView!

    @IBOutlet weak var settingButton: UIButton!


    override func viewDidLoad() {
        super.viewDidLoad()

        self.backGround?.frame = CGRect(x: 0, y: 0, width: screenWidth1, height: screenHeight1)
        self.logo.frame = CGRect(x: screenWidth1 * 1 / 2 - screenWidth1 / 6, y: 0, width: screenWidth1 / 3, height: screenWidth1 / 3)


    }
}

(This is the file for the Main Menu)

EDIT 1:

The problem was that I should have changed UINavigationController to UINavigationController but now , there is another problem : the "playButton" is supposed navigate to another page but when I press it , again , I get "Unexpectedly found nil while unwrapping an Optional value".

Edit 2 : So , I solved both of the problems but now , in another page I have this function :

func goToMain(){
    self.present(MainNavigation(), animated: true, completion: nil)

}

but when the function is being run , instead of going to the main page (MainNavigation) , It gives the same problem for the "play button". Why?

Answer 1

Why are you attaching view objects to your navigation controller? You want to push view controllers onto your navigation controller's stack, but it's not normal to put views in your navigation controller.

That's likely your problem.