NSTimer "target: self" returns error "Unresolved identifier"

Question

I trying to make a "pet", and want the hunger to decrease every x-minute. But every time I use the NSTimer and say that "target: self" I get an error?

Code snippet:

var hunger = 10

var timer = NSTimer(timeInterval: 10, target: self, selector: Selector(decreaseHunger()), userInfo: nil, repeats: true)

func decreaseHunger(){ hunger -= 1 }

Answer 1 · 2016-10-16T21:21:12Z

October 16, 2016 9:21pm

You have to be within an object to reference self, which refers to the current instance of that object.

More importantly, I think you have to add a timer to a run loop, something which I honestly couldn't help you with. However, there is a class method that will do what you want - Timer.scheduledTimer. I whipped this up in a playground, worked like a charm:

import UIKit
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

class Pet {

    var hunger = 10
    var timer: Timer?

    init() {
        timer = Timer.scheduledTimer(withTimeInterval: 2, repeats: true) { (timer) in
            if self.isFull() {
                timer.invalidate()
                print("Your pet is full!")
            } else {
                self.hunger -= 1
                print(self.hunger)
            }
        }
    }

    func isFull() -> Bool {
        return self.hunger == 0
    }
}

let pet = Pet() // Prints 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, Your pet is full!

Note how you have to make import the PlaygroundSupport framework to make the playground run indefinitely(by default, it'll stop once it reaches the end of your code). Also note this is Swift 3, might be slightly different if you're using Swift 2.

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Christian Bjørtomt

Christian Bjørtomt

NSTimer "target: self" returns error "Unresolved identifier"

1 Answer

Oliver Duncan

Oliver Duncan