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
    }
}

Does centerContainer need to be a property? Will it be access from other code besides the didFinishLaunchingWithOptions method? — rmaddy
– rmaddy, Commented May 5, 2017 at 16:36

Paulo Mattos · Accepted Answer · 2018-05-31 16:56:01Z

8

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.

edited May 31, 2018 at 16:56

answered May 5, 2017 at 16:30

Paulo Mattos

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Comments

John Montgomery · Accepted Answer · 2017-05-05 16:34:43Z

Since centerContainer isn't an optional and isn't given a default value, Swift expects an initializer function to give it one. There are a few possible solutions here:

Give it a default value. Probably not practical in this context.
Make it optional. Would work, but depending on how it's used might add a lot of unnecessary unwrapping to your code.
Make it an implicitly unwrapped optional. This is essentially saying "I can't/don't want to give this a default value or set it in an initializer, but I will definitely be giving it a value before I use it for anything." Usually the cleanest option for things like this, just be careful that you don't assign it nil at any point later in your code or things will break.

nayem · Accepted Answer · 2017-05-05 16:35:15Z

0

Make your centerContainer var optional like window. In swift, all of the properties must be initialized. When you make your var optional, you are initializing it as nil.

var centerContainer: MMDrawerController?

answered May 5, 2017 at 16:35

nayem

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3 Comments

Paulo Mattos Over a year ago

Using an implicitly unwrapped optional here (ie, MMDrawerController!) might be a better fit here. See my answer below.

nayem Over a year ago

@PauloMattos Yes! That's absolutely right. But as the OP had some basic knowledge on optional (he had used one as window) I hope _not bragging some more concept_(that is, implicit optional) would be good for him.

Paulo Mattos Over a year ago

Good point man, I agree! A concepts overload -- a common behavior on SO, one may say -- might scary him away. Sometimes you need to learn a trick at time :)

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