How do I resolve error "Class appDelegate has no initializers"?

Question

I'm receiving the error:

Class AppDelegate has no initializers

and cannot seem to understand why. I am following this tutorial. I am a beginner so any help would be VERY appreciated!

My code:

import UIKit

@UIApplicationMain

class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    var centerContainer: MMDrawerController

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.

        _ = self.window!.rootViewController

        let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)

        let centerViewController = mainStoryboard.instantiateViewController(withIdentifier: "ViewController") as! ViewController

        let leftViewController = mainStoryboard.instantiateViewController(withIdentifier: "LeftSideViewController") as! LeftSideViewController

        let leftSideNav = UINavigationController(rootViewController: leftViewController)
        let centerNav = UINavigationController(rootViewController: centerViewController)


        centerContainer = MMDrawerController(center: centerNav, leftDrawerViewController: leftSideNav)


        centerContainer.openDrawerGestureModeMask = MMOpenDrawerGestureMode.panningCenterView;

        centerContainer.closeDrawerGestureModeMask = MMCloseDrawerGestureMode.panningCenterView;

        window!.rootViewController = centerContainer
        window!.makeKeyAndVisible()

        return true
    }
}

Answer 1

Try changing your centerContainer property to an optional like this:

var centerContainer: MMDrawerController!

as such, it will be initialized with nil, which should be enough to remove the error you are having. (By the way, you shouldn't need to change the rest of your code as a result.)

From The Swift Programming Language book:

Classes and structures must set all of their stored properties to an appropriate initial value by the time an instance of that class or structure is created. Stored properties cannot be left in an indeterminate state.