Difference between static in swift and static in java

Question

Can anybody explain me the difference between static variables in swift vs static variables in java?

I know that the static functions in java execute while the memory gets allocated and not when the instance is created for an object.

I was trying to make a singleton in swift, I saw that the function call for getInstance() in my ViewController viewDidLoad function was executing before my static variables get populated and therefore I am returning nil values.

How do I approach this problem? Should I find an "Initializer" sort of a function where all the allocations and initializations for classes happen so this works smoothly?

Please advise

I am adding a code snippet for the same

class X {
     var xInstance:X = X() 
     public static func getInstance() { return xInstance } 
}

class Y {
   var xInstance: X?
   var yInstance: Y = Y()
   public override init() {
    xInstance = X.getInstance()

    public static func getInstance() {
       return yInstance
    }
}


class someView: UIView {

   public override init() {
    var xInstance = X.getInstance()   //This is my problem area. I am seeing nil for xInstance  
   }

}

I am seeing nil values for xInstance. What am I doing wrong?

Can you show some code? as far as I know, there is not much of difference. — Peyman
– Peyman, Commented Nov 25, 2015 at 23:33

Mark · Accepted Answer · 2015-11-26 00:40:49Z

1

To me it sounds like you're not declaring your singleton correctly, more code would help. But for a quick solve, and just out of assumption - here is a quick easy way to declare a singleton with Swift 1.2

static let sharedInstance = Object()
@objc private override init() {} //This prevents others from using the default '()' initializer for this class

and then to use the singleton would be

Object.sharedInstance.fuctionName()

answered Nov 26, 2015 at 0:40

Mark

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世人都晓神仙好 · Accepted Answer · 2015-11-26 06:48:17Z

0

In your original code snippet, xInstance is an instance attribute that needs to be initialized when an instance of X is created.

Static method getInstance() cannot access instance attributes or methods. (And hey! You're missing return type for the getInstance() method).

The easiest way to do a singleton with Swift these days is like this:

public class A {
    public static let sharedInstance = A()
}

And A.sharedInstance will be the singleton instance.

If you don't want others do A() manually outside this file, add a private init() {} line.

If you still prefer the X.getInstance() way, add a public static func getInstance() { return sharedInstance } line.

answered Nov 26, 2015 at 6:48

世人都晓神仙好

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1 Comment

Katakam Nikhil Over a year ago

I still see nil value for xInstance when I fire the getInstance or even do X.xInstance. The line public static let sharedInstance = A() executes after the getInstance is called. Can you please tell me why?

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