Timer.fire() not working after invalidating in Swift - swift

Question

After using
#IBAction func pauseButton(sender: AnyObject) {
if isPaused == false {
timer.invalidate()
isPaused = true
displayLabel.text = "\(count)"
println("App is paused equals \(isPaused)")
} else if isPaused == true {
var isPaused = false
timer.fire()
// timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("updateTime"), userInfo: nil, repeats: true)
}
}
to pause the app, i'd like to hit pause again, in which case, the timer will continue to count from where it left off.
Additionally, when i press pause/play too many times, multiple instances of the timer occur which will cause the timer to increase a few times per second.
Please help!
//
// ViewController.swift
// Navigation Bars
//
// Created by Alex Ngounou on 8/27/15.
// Copyright (c) 2015 Alex Ngounou. All rights reserved.
//
import UIKit
class ViewController: UIViewController {
var timer = NSTimer()
var count = 0
var isPaused = false
func updateTime() {
switch count {
case 0, 1:
count++
println( "\(count) second.")
displayLabel.text = "\(count)"
case 2:
count++
println("\(count) seconds.")
displayLabel.text = "\(count)"
default:
count++
println("\(count) seconds.")
displayLabel.text = "\(count)"
}
}
**strong text**#IBAction func playButton(sender: AnyObject) {
var isPaused = false
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("updateTime"), userInfo: nil, repeats: true)
}
#IBAction func stopButton(sender: AnyObject) {
timer.invalidate()
count = 0
displayLabel.text = "0"
}
// if it's currently paused, pressing on the pause button again should restart the counter from where it originally left off.
#IBAction func pauseButton(sender: AnyObject) {
if isPaused == false {
timer.invalidate()
isPaused = true
displayLabel.text = "\(count)"
println("App is paused equals \(isPaused)")
} else if isPaused == true {
var isPaused = false
timer.fire()
// timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("updateTime"), userInfo: nil, repeats: true)
}
}
#IBAction func resetButton(sender: AnyObject) {
timer.invalidate()
count = 0
displayLabel.text = ""
}
#IBOutlet weak var displayLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("updateTime"), userInfo: nil, repeats: true)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}

Answer 1

From: https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSTimer_Class/
Once invalidated, timer objects cannot be reused.
So essentially an NSTimer will do nothing at all once invalidated. Your timer property must be assigned to a newly constructed NSTimer object after that point to get it to fire again. If your invalidation bookkeeping is accurate, there is no "buildup" problem of multiple timers.
Probably the easiest method to your actual problem, though, is logical filtering. That is, keep the NSTimer object around indefinitely and let it fire continually. When the stored property isPaused is true, you ignore timer events (by returning immediately from the processing function), otherwise you process them.

Answer 2

a "lazier" approach can be otherwise useful:
class ViewController: UIViewController {
var timer: Timer?
override func viewDidLoad() {
super.viewDidLoad()
startTimer()
}
final func killTimer(){
self.timer?.invalidate()
self.timer = nil
}
final private func startTimer() {
// make it re-entrant:
// if timer is running, kill it and start from scratch
self.killTimer()
let fire = Date().addingTimeInterval(1)
let deltaT : TimeInterval = 1.0
self.timer = Timer(fire: fire, interval: deltaT, repeats: true, block: { (t: Timer) in
print("hello")
})
RunLoop.main.add(self.timer!, forMode: RunLoopMode.commonModes)
}

Answer 3

Declare your timer as 'weak var' like this:
weak var timer: Timer?