Swift - Issue trying to access to Singleton object

Question

I am trying to implement the Singleton pattern on my app, without success so far. When I try to access my Singleton, it seems that the program is not accessing the real singleton, but a copy of it instead. Since this copy was not initialized, my app crashes, showing this error:

fatal error: unexpectedly found nil while unwrapping an Optional value

Here is an example of code I made:

import UIKit

class ViewController: UIViewController {

    static let sharedViewController = ViewController()

    var name: String = "Billy"
    var age: Int = 12

    override func viewDidLoad() {
        super.viewDidLoad()

        println("Old name from ViewController: \(name)")
        println("Old age from ViewController: \(age)")

        name = "Jack"
        age = 45

        println("New name from ViewController: \(name)")
        println("New age from ViewController: \(age)")

        println("singleton name from ViewController: \(ViewController.sharedViewController.name)")
        println("singleton name from ViewController: \(ViewController.sharedViewController.age)")
    }
}

As you can see, this is very simple. The class has two attributes initialized at creation, which are modified in viewDidLoad(). First, I try to access the attributes directly, and, then, through the Singleton.

Here is the output:

Old name from ViewController: Billy
Old age from ViewController: 12
New name from ViewController: Jack
New age from ViewController: 45
singleton name from ViewController: Billy
singleton name from ViewController: 12

As you can see, the data is still the same from the singleton point of view. Unfortunately, the young Billy will never grow up.

I implemented all the three approaches of Singleton pattern in Swift, as it was said on this topic: dispatch_once singleton model in swift, without any success.

I do not understand why I cannot access the real Singleton and only a copy of it (which is bad for a Singleton pattern).

Thank you for your help.

Answer 1

I think, eventually, you won't be making a singleton of an UIViewController. What you probably want is to create a class, like Person.

Still if you wan't to do it like you did static let sharedViewController = ViewController() isn't the same object as self.

import UIKit

class ViewController: UIViewController {

    static let sharedViewController = ViewController()

    var name: String = "Billy"
    var age: Int = 12

    override func viewDidLoad() {
        super.viewDidLoad()

        println("VC - Name : \(name)")
        println("VC - Age : \(age)")

        println("Singleton - Name : \(name)")
        println("Singleton - Age : \(age)")

        ViewController.sharedViewController.name = "Jack"
        ViewController.sharedViewController.age = 45

        println("VC - Name : \(name)")
        println("VC - Age : \(age)")

        println("Singleton - Name : \(ViewController.sharedViewController.name)")
        println("Singleton - Age : \(ViewController.sharedViewController.age)")

    }
}

Console :

VC - Name : Billy
VC - Age : 12
Singleton - Name : Billy
Singleton - Age : 12
VC - Name : Billy
VC - Age : 12
Singleton - Name : Jack
Singleton - Age : 45

Anyway, try to document yourself a bit more on the Singleton pattern :-)