Swift: Global variable not updating

Question

In a file called Menu, I have this:

class Menu: UIViewController {
var no_of_swipes = 99

@IBAction func pressedThreeSwipes(sender: AnyObject) {
    no_of_swipes = 3
}
}

And in another file I have this: class Game: UIView {

func didMoveToView(view: UIView) {
    /* Setup your scene here */

    var swipes = Menu()

    var no_of_swipes: Int = 0 {
        didSet {
            println("\(swipes.no_of_swipes) should be three")
        }
    }
}

However when I press the button in Menu, triggering a segue that moves to the second file. The console states that no_of_swipes = 0. In // line x, if I remove = 0, I receive an error about having an initialiser. So, my question is: why isn't no_of_swipes 3? I think this is a problem either with obtaining no_of_swipes or with the observer.

Thank you in advance

You're not accessing the same instance of `Menu`, but creating a new one. To access that instance of `Menu` in a different view controller you can pass it in. — Lyndsey Scott, Jan 01 '15 at 13:51
You have declared `no_of_swipes` two times. They are different variables. Omit the one on top. — qwerty_so, Jan 01 '15 at 13:55
@ThomasKilian Please could you give a more detailed answer. Thank you. — William Clark, Jan 01 '15 at 14:14

qwerty_so · Answer 1 · 2015-01-01T15:24:53.513

3

Your problem is that you misunderstood the rationale for didSet. This is performed when you assign something to a property. Paste the following in Playground.

class Menu {
  var no_of_swipes = 5

  @IBAction func pressedThreeSwipes(sender: AnyObject) {
    no_of_swipes = 3
  }

}

var swipes = Menu()
var no_of_swipes: Int = 0 { //line x
didSet {
  println("i have been changed, and \(swipes.no_of_swipes) is what we do not get")
}
}

no_of_swipes = 99
println(no_of_swipes)
no_of_swipes = swipes.no_of_swipes
println(no_of_swipes)

I hope it's self explanatory.

To amend according to the comments:

class Menu {
  var no_of_swipes = 5
  var subscriber:((Int)->())?

  @IBAction func pressedThreeSwipes(sender: AnyObject) {
    no_of_swipes = 3
    subscriber?(no_of_swipes) // for convenience pass the number
  }

}

class MyOtherClass {
  var swipes = Menu()
  init() {
      swipes.subscriber = myActionOnSwipe
  }

  func myActionOnSwipe(swipes:Int) {
    println("Swipes is \(swipes)")
  }
}

If you add the following (also in Playground):

let c1 = MyOtherClass()
c1.swipes.pressedThreeSwipes(c1)

you will see how it works.

edited Jan 01 '15 at 15:24

answered Jan 01 '15 at 14:32

qwerty_so

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Thank you. Please answer me: How can I code it so that when pressedThreeSwipes is pressed, the didSet, says 'no_of_swipes is three'. Thank you. – William Clark Jan 01 '15 at 14:40
If you could include how to do that in your answer I will tick and +1 – William Clark Jan 01 '15 at 15:03
Thanks for the edit. One thing with the init - I get the error 'Initialisers may only be declared in a type.' – William Clark Jan 01 '15 at 16:09
I get what you're doing but it feels too complicated. Surely I should just fix what I've already done. Do you have an alternate answer? – William Clark Jan 01 '15 at 19:00
Thanks for taking back the vote. Go and get your help elsewhere. – qwerty_so Jan 01 '15 at 20:18
There's no need to be hostile. I'm just asking a question and I find that your answer isn't appropriate. – William Clark Jan 02 '15 at 10:17

Swift: Global variable not updating

1 Answers1