Change between multiple view controllers causing app to crash; Tab View; Swift - ios

Question

Apologies for this one, I'm sure that I'm missing a swift fundamental here.
I have a navigation app that I'm working on in swift.
Earlier on I made it as a single view and have changed it to a tab bar controller application.
In the background the location manager does its work and when is does the update locations work it displays the lat and long on a label.
When the app was a single view app this was no problem however now that it is a tab bar app, as soon as I change to a different tab when the location manager function fires it crashes the app with the following code (which I suspect means nothing much on its own) EXC_BREAKPOINT (code=1, subcode=0x10039bb54
I strongly suspect that I am doing something fundamentally wrong with trying to update a label on a view controller that is not active at the time.
distanceLabel.text = "Currently \(distanceText) from destination"
lbl_location.text = String(mylat) + ", " + String(mylong)
I have copied in all of my code below only taking out a few sensitive bits so that you can see the big picture.
Open to constructive feedback as to better coding practices.
Thanks
Bruce
import UIKit
import CoreLocation
class ViewController: UIViewController, CLLocationManagerDelegate {
//in the original view controller which has now been incorporated into tabs
#IBOutlet weak var distanceLabel: UILabel!
#IBOutlet weak var lbl_location: UILabel!
//on a new view controller on another tab
#IBOutlet weak var employeeNameSetup: UITextField!
#IBOutlet weak var employeeNumberSetup: UITextField!
#IBOutlet weak var contactNumberSetup: UITextField!
#IBOutlet weak var managerNameSetup: UITextField!
#IBOutlet weak var managerEmailSetup: UITextField!
#IBOutlet weak var adminPasswordSetup: UITextField!
#IBAction func setAppDefaults(_ sender: Any) {
if (employeeNameSetup.text?.isEmpty)! || (employeeNumberSetup.text?.isEmpty)! || (contactNumberSetup.text?.isEmpty)! || (managerNameSetup.text?.isEmpty)! || (managerEmailSetup.text?.isEmpty)!{
let noGoAlert = UIAlertController(title: "Insufficient Fields Filled out", message: "Only the Password field is optional, please fill out all other fields before pressing button", preferredStyle: .alert)
let defaultAction = UIAlertAction(title: "Close Alert", style: .default, handler: nil)
noGoAlert.addAction(defaultAction)
present(noGoAlert, animated: true, completion: nil)
}
else{
let defaults = UserDefaults.standard
defaults.set(employeeNameSetup.text, forKey: "employeeName")
defaults.set(employeeNumberSetup.text, forKey: "employeeNumber")
defaults.set(contactNumberSetup.text, forKey: "contactNumber")
defaults.set(managerNameSetup.text, forKey: "managerName")
defaults.set(managerEmailSetup.text, forKey: "managerEmail")
}
}
#IBAction func submit_button(_ sender: Any) {
uploadData()
}
let location_process = CLLocationManager()
var mylat :Double = 0
var mylong :Double = 0
var destination = CLLocation(latitude: #####, longitude: #####)
var distanceToDest :Int = 0
var dburl = NSURL(string: "#########")
let contact_name = "#####"
let contact_number = "#####"
let unique_id = "###"
let employee_number = "#####"
var distanceText = ""
var runOnce = false
var isAdmin = false
var adminPassword = "#######"
func sendEmail(messageText: String){
let url = URL (string: "########")
let session = URLSession.shared
var request = URLRequest(url: url!)
request.httpMethod = "POST"
let paramtosend = #########
request.httpBody = paramtosend.data(using: String.Encoding.utf8)
let task = session.dataTask(with: request)
task.resume()
}
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
let mylocation = locations[0]
mylat = mylocation.coordinate.latitude
mylong = mylocation.coordinate.longitude
distanceToDest = Int(mylocation.distance(from: destination))
if distanceToDest > 1000 {
distanceText = String(Int(distanceToDest/1000))
distanceText = distanceText + " km"
}
else if distanceToDest < 100 {
let current_date_time = Date()
let formatter = DateFormatter()
formatter.dateStyle = .medium
formatter.timeStyle = .medium
formatter.dateFormat = "HH:mm dd MMM yyyy"
formatter.timeZone = TimeZone.autoupdatingCurrent
let timestamp = formatter.string(from: current_date_time)
if !runOnce {
sendEmail(messageText: "\(contact_name); Employee \(employee_number) Arrived at destination \(destination.coordinate.latitude), \(destination.coordinate.longitude) at \(timestamp)")
}
distanceText = String(distanceToDest)
distanceText = distanceText + " m"
runOnce = true
}
else {
distanceText = String(distanceToDest)
distanceText = distanceText + " m"
}
distanceLabel.text = "Currently \(distanceText) from destination"
lbl_location.text = String(mylat) + ", " + String(mylong)
uploadData()
}
#IBAction func uploadData()
{
var httprequest = URLRequest(url: dburl! as URL)
httprequest.httpMethod = "POST"
var dataString = "####" // starting POST string with a secretWord
// the POST string has entries separated by &
dataString = dataString + "&unique_id=" + unique_id
dataString = dataString + "&mylat=" + String(mylat) // add items as name and value
dataString = dataString + "&mylong=" + String(mylong)
dataString = dataString + "&contact_name=" + contact_name
dataString = dataString + "&contact_number=" + contact_number
dataString = dataString + "&employee_number=" + employee_number
let current_date_time = Date()
let formatter = DateFormatter()
formatter.dateStyle = .medium
formatter.timeStyle = .medium
formatter.dateFormat = "HH:mm dd MMM yyyy"
formatter.timeZone = TimeZone.autoupdatingCurrent
let timestamp = formatter.string(from: current_date_time)
dataString = dataString + "&timestamp=" + timestamp
// convert the post string to utf8 format
let dataD = dataString.data(using: .utf8) // convert to utf8 string
do
{
// the upload task, uploadJob, is defined here
let uploadJob = URLSession.shared.uploadTask(with: httprequest, from: dataD!)
//let uploadJob = URLSession.shared.uploadTask(with: httprequest, from: dataD)
uploadJob.resume()
}
}
override func viewDidLoad() {
super.viewDidLoad()
location_process.delegate = self
location_process.pausesLocationUpdatesAutomatically = false
location_process.desiredAccuracy = kCLLocationAccuracyBest
location_process.requestWhenInUseAuthorization()
location_process.requestAlwaysAuthorization()
if CLLocationManager.locationServicesEnabled()
{
location_process.distanceFilter = 50
location_process.allowsBackgroundLocationUpdates = true
location_process.startUpdatingLocation()
}
// 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.
}
}