Unexpected crash when ApplicationDidEnterBackground: NSTimer

Question

Yesterday, I've ask because I have a problem with my timer in background, I've found a solution to make it works but now, I got a problem when my application enter in background.

Run in background:

backgroundTaskIdentifier = UIApplication.shared.beginBackgroundTask(expirationHandler: {
        UIApplication.shared.endBackgroundTask(self.backgroundTaskIdentifier!)
    })

This is my timer:

let interval = 0.01
timer = Timer.scheduledTimer(timeInterval: interval, target: self, selector:#selector(ViewController.updateTimer), userInfo: nil, repeats: true)
RunLoop.main.add(timer, forMode: RunLoopMode.commonModes)

This is my updateTimer function:

func updateTimer () {
    var j = 0
    for _ in rows {
      if (rows[j]["Playing"] as! Bool == true ) {
            rows[j]["time"] = (rows[j]["time"] as! Double + interval) as AnyObject
            rows[j]["lastTime"] = (rows[j]["lastTime"] as! Double + interval) as AnyObject
      }
      if (rows[j]["lastTime"] as! Double > 60.0) {
            min[j] += 1
            rows[j]["lastTime"] = 0.00 as AnyObject
      }
      j += 1
    }
}

In my applicationDidEnterBackground method I call this function:

func backgroundTimer() {
    print("background") // This Print works fine
    timer.invalidate() // Never works
    interval = 1.00 // Crash when interval change from 0.01 to 1.00
    timer = Timer.scheduledTimer(timeInterval: interval, target: self, selector:#selector(ViewController.updateTimer), userInfo: nil, repeats: true)
}

And this is my output when my application enter in background:

The Double is interval.

In Info.plist I add : Application does not run in background : NO.

Let me know what i'm doing wrong?

EDIT:

Initialization of rows in viewDidLoad method

let i: [String : AnyObject] = ["time": time as AnyObject, "Playing": false as AnyObject, "lastTime": 0.00 as AnyObject, "lapNumber": 0 as AnyObject, "min": 0 as AnyObject]
rows.append(i as [String : AnyObject])

@AmeyaVichare Thanks for your answer. It can't be nil and it was not nil in foreground, I don't understand why it can be in background — pierreafranck, Oct 10 '17 at 08:51
What do you see if you use the debugger to print j and rows[j] at the time of the crash? — Phillip Mills, Oct 10 '17 at 14:21
@PhillipMills this is the last line before the crash: `Rows: ["lastTime": 3.989999999999959, "min": 0, "time": 3.989999999999959, "lapNumber": 0, "Playing": 1]` & `j: 0` J = 0 cause I have only one row, so it's normal — pierreafranck, Oct 10 '17 at 14:27

Phillip Mills · Answer 1 · 2017-10-10T14:55:20.017

1

Your basic problem seems to be the use of AnyObject for things that are not really objects. It causes the as! Bool to fail.

Here's a playground snippet that gets back a stored Bool value by allowing simple values in the dictionary.

var rows: [[String : Any]] = []
let i: [String : Any] = ["time": time, "Playing": false, "lastTime": 0.00, "lapNumber": 0, "min": 0]
rows.append(i)

let playing = rows[0]["Playing"]
if let playing = playing as? Bool {
    print("Bool")
} else {
    print("Something else \(String(describing: playing))")
}

edited Oct 10 '17 at 14:55

answered Oct 10 '17 at 14:48

Phillip Mills

30,888
4
42
57

Thanks for your answer. I've test this way but same result when appDidEnterBackground :'( – pierreafranck Oct 11 '17 at 07:21
If you used Phillip snippet then you crash due to unwrapping nil value should be gone... so you should have different crash now... – Tomasz Czyżak Oct 11 '17 at 08:20

pierreafranck · Answer 2 · 2017-10-11T14:43:42.437

I found solution for this problem.

Using NSNotification.

override func viewWillAppear(_ animated: Bool) {
  NotificationCenter.default.addObserver(self, selector:#selector(ViewController.backgroundTimer), name:NSNotification.Name.UIApplicationDidEnterBackground, object: nil)

  NotificationCenter.default.addObserver(self, selector:#selector(ViewController.backToForeground), name:NSNotification.Name.UIApplicationWillEnterForeground, object: nil)
}

func backgroundTimer(notification : NSNotification) {
    self.timer.invalidate()
    interval = 1.00
    timer = Timer.scheduledTimer(timeInterval: interval, target: self, selector:#selector(ViewController.updateTimer), userInfo: nil, repeats: true)
    RunLoop.main.add(timer, forMode: RunLoopMode.commonModes)
}

func backToForeground(notification: NSNotification) {
    self.timer.invalidate()
    interval = 0.01
    timer = Timer.scheduledTimer(timeInterval: interval, target: self, selector:#selector(ViewController.updateTimer), userInfo: nil, repeats: true)
    RunLoop.main.add(timer, forMode: RunLoopMode.commonModes)
}

Don't forgot to add the backgroundTaskIdentifier.

score 1 · Answer 3 · answered Oct 11 '17 at 14:56

1

I suppose you are using the AppDelegate mainVC method that create a copy of your main. Thats why your timer are never invalidate in your ViewController. It is invalidate in your copy. Check out this answer: Pausing timer when app is in background state Swift

answered Oct 11 '17 at 14:56

Nicholas Maja

21
5

Thanks. I already use this answer for solve my problem ! Look at my answer :) – pierreafranck Oct 11 '17 at 14:56

Unexpected crash when ApplicationDidEnterBackground: NSTimer

3 Answers3