Timer counts but doesn´t desplay - swift

Question

I just started to learn how to code and speak English^^
When I go from secondViewController to ViewController, a timer starts. A label shows the timer.
My problem is, when I go from secondViewController to ViewController for the second time, the label doesn´t show the timer. But the timer continue to count (I printed it out). Why the label doesn´t shoews the timer ?
I would be very grateful for your help
ViewController
var habit = 0
var statusFirst = false
class ViewController: UIViewController {
var firstTitel = ""
var secondTitels = ""
var timerTime = 0
var timer = Timer()
#IBOutlet weak var titelLabel: UILabel!
#IBOutlet weak var dateLabel: UILabel!
#IBOutlet weak var secondTitel: UILabel!
#IBOutlet weak var secondDate: UILabel!
#objc func processTimer() {
timerTime += 1
dateLabel.text = String(timerTime)
print(timerTime)
}
override func viewDidLoad() {
super.viewDidLoad()
// Hide Label - START
print(habit)
if habit == 0 {
titelLabel.isHidden = true
secondTitel.isHidden = true
dateLabel.isHidden = true
secondDate.isHidden = true
timer.invalidate()
}else if habit == 1 {
titelLabel.isHidden = false
secondTitel.isHidden = true
dateLabel.isHidden = false
secondDate.isHidden = true
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ViewController.processTimer), userInfo: nil, repeats: true)
}else if habit == 2 {
titelLabel.isHidden = false
secondTitel.isHidden = false
dateLabel.isHidden = false
secondDate.isHidden = false
}
// Hide Label - END
let titelObject = UserDefaults.standard.object(forKey: "firstTitel")
if let titel = titelObject as? String {
titelLabel.text = titel
}
let titellObject = UserDefaults.standard.object(forKey: "secondTitel")
if let titell = titellObject as? String {
secondTitel.text = titell
}
// Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
SecondViewController
class SecondViewController: UIViewController {
var titelSecondViewController = ""
var dateSecondViewController = 0
#IBOutlet weak var titelField: UITextField!
#IBOutlet weak var dateField: UITextField!
#IBOutlet weak var okButton: UIButton!
#IBAction func okButtonAction(_ sender: Any) {
titelSecondViewController = titelField.text!
if let datefield = dateField.text {
if datefield == "" {
dateSecondViewController = 0
}else{
dateSecondViewController = Int(datefield)!
}
}else{
print("lol")
}
}
override func viewDidLoad() {
super.viewDidLoad()
}
// Segue - Start
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "toViewController" {
let viewController = segue.destination as! ViewController
habit += 1
print(habit)
if habit == 1 {
statusFirst = true
UserDefaults.standard.set(titelSecondViewController, forKey: "firstTitel")
}else if habit == 2{
UserDefaults.standard.set(titelSecondViewController, forKey: "secondTitel")
}else{
return
}
}
}
// Segue - End
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}

Answer 1

In first case habit = 1 so the timer is called
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ViewController.processTimer), userInfo: nil, repeats: true)
since the timer has a strong reference and you don't invalidate() it inside viewDidDisappear , it keeps the VC in memory after you dismiss it
//
In second time habit = 2 and you don't init the time inside it's if statement then the label of the second instance ( the presented one ) doesn't update , while the hidden dismissed one do