CODEWITHSUNDEEP
iosswift
Scrungepipes
Scrungepipes

Reputation: 37581

Swift: How to declare a static member variable which is a class

I'm trying to declare a class which has a static variable which I want to set to an object of the class i.e.

class MyViewController: UIViewController {
      @IBOutlet weak var title: UILabel!

      static var staticSelf:MyViewController

This declaration generates the following error:

"class var declaration requires an initializer expression or getter/setter specifier".

So I tried several attempts at adding an initialzer but just was getting more or different compilation errors. So instead I tried adding a getter/setter specifier as it says in the error, but this is resulting in an infinite loop when run. I've tried several versions, this is the latest:

class MyViewController: UIViewController {

  @IBOutlet weak var title: UILabel!

  static var staticSelf:MyViewController {
    set (selfInstance) {
        MyViewController.staticSelf = selfInstance
    }
    get {
        return MyViewController.staticSelf
    }
  }

  override func viewDidLoad() {
    super.viewDidLoad()
    MyViewController.staticSelf = self
  }
}

The initial attempt at the implementation of the setter method was staticSelf = selfInstance, XCode flagged this as an error and auto-corrected to self.staticSelf = selfInstance, but that results in an infinate loop, so I changed it to MyViewController.staticSelf = selfInstance, but that too creates an infinate loop.

I've tried a thousand things to get this set up and could have done it in 3 seconds with objective-C , and am getting very fed up with Swift right now.

Upvotes: 7

Views: 24689

Answers (3)

ryantxr
ryantxr

Reputation: 4219

Assuming that in objective-c you would have used a pointer that could be null, in Swift, you do something similar.

class MyViewController: UIViewController {
    static var staticSelf:MyViewController?
    override func viewDidLoad() {
        super.viewDidLoad()
        MyViewController.staticSelf = self
    }    

    func somefunc() {
    }
}

When you need to access it from elsewhere:

if let controller = MyViewController.staticSelf {
    controller.somefunc()
}

Upvotes: 4

Sulthan
Sulthan

Reputation: 130082

The basic example

class MyClass {
    static var string: String
}

does not work because unitialized variables have nil value. However, in Swift you can assign nil only to optional variables.

You have two options:

  1. Declare the variable as optional

    static var string: String?

    or

    static var string: String? = nil

  2. Initialize with a non-nil value:

    static var string: String = "some value"

If your aim is to create a singleton, then see the official Apple guide for the solution:

class MyViewController: UIViewController {
    static let staticSelf = MyViewController()
}

Upvotes: 14

Lasse
Lasse

Reputation: 650

You need to assign the value right away in the declaration line:

    static var staticSelf = MyViewController()

This is, btw. the standard pattern to create a singleton in Swift.

Upvotes: 3

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