Unexpected crash when ApplicationDidEnterBackground: NSTimer - swift

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])

Answer 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))")
}

Answer 2

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.

Answer 3

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