Swift: test for expiration / invalidation of NSTimer seems to fail

Question

Using Swift, I'm having difficulty testing for the expiration / invalidation of an NSTimer.

In particular, why does it appear that a test like while timer1 != nil { } or while timer1?.valid { } does not escape the null loop after it has been seemingly clearly invalidated and set to nil directly.

I have reviewed several of the questions relating to NSTimer already, and unless there is a version in Obj-C that I simply am not recognizing as the same issue due to my poor comprehension of ObjC properly, I don't believe this is covered (directly).

Please note, I'm not looking to directly "fix" the code, I'm looking for comprehension.

//  ViewController.swift
//  NSTimerTest


import UIKit

class ViewController: UIViewController {

    var z:Int = 0
    var timer1:NSTimer? = nil

    @IBOutlet var lblMessage: UILabel
    @IBOutlet var lbl2: UILabel
    @IBAction func btnPress(sender: AnyObject) {
        doBtnPress()
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        z = 0
        lblMessage.text = "Timer was called \(z) times."
        lbl2.text = "waiting for countdown"

    }


    func doBtnPress(){
        lblMessage.text = "doBtnPress!!"
        timer1 = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: "doTimedAction", userInfo: nil, repeats: true)

        // All of the below infinitely loop 
        // while timer1?.valid { }  // <=== never escapes, also depreciated in IOS 8.0 ???
        // while timer1 { }       // <==== never escapes
        // while timer1 != nil { } // <==== never escapes 
        // while z >= 0 { }       //  <==== test counter instead, but no use 


        lbl2.text = "timer has been invalidated"
    }

    func doTimedAction(){
        lblMessage.text = "Timer was called \(++z) times."

        if z >= 10 {
            timer1?.invalidate()
            timer1 = nil
            z = -1      
        }

    }     
}

As you can see, I have two labels -- one that is simply updated with the number of times the NSTimer has been invoked, and the other that hold be updated after I invalidate the timer.

With the testing lines commented out as noted above, things work as I expect. The label indicating the number of timer invocations updates each second (or so) and the immediate but factually incorrect display of the statement that "Timer has been invalidated" )

However, it my expectation that de-commenting any of the three lines that follow should allow the timer to run through 10 iterations, and then be invalidated, allowing the "Timer invalidated" message to display. Instead, however, I end up stuck infinitely in the empty loop, as if the condition(s) never come true. The UI does not update at all.

Instead of testing the timer, I also tried testing the counter z, but this does not work either, leading me to believe there is something more elemental at play that I am not understanding. For example, using while z >= 0 { println("z is \(z)")} in the location results in z is 0 -- the reason the loop is infinite. But again, if I comment out the line, z does in fact clearly increment, as the label DOES change, reflecting the cane in the counter z.

Again, I'm looking more to understand WHY things are failing (i.e., what I am failing to comprehend here). I understand, for example, I could make this "work" by having the doTimedAction() func directly update the label --- but that would not help me understand why my tests fail.

Swift: test for expiration / invalidation of NSTimer seems to fail

Answers (1)

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