Making the app save data when the app terminates - ios

Question

I already know how to save things and I can automatically load them when opening the app. But I have no idea how to save them as it closes! I have a button for now. I am trying to save just one value, StreakNumber. However, whenever I try, I fail.
When in app delegate I try saying ViewController.AppSave(ViewController). I get an error:
Editor placeholder in source file
Expression resolves to an unused function
and if I use ViewController.AppSave()
I get the following error:
Instance member 'SaveApp' cannot be used on type 'ViewController'; did you mean to use a value of this type instead?
import UIKit
import UserNotifications
class ViewController: UIViewController {
//TEST PLAY AREA//
#IBAction func SaveButton(_ sender: Any) {
SaveApp()
}
#IBAction func LoadButton(_ sender: Any) {
LoadApp()
}
///TEST PLAY AREA ENDS
public var streakNumber = 0
public var streakNumberString = ""
public var activated = false
let defaults = UserDefaults.standard
//Labels
#IBOutlet var streakNumberLabel: UILabel!
#IBOutlet var remainingTimeTextLabel: UILabel!
#IBOutlet var remainingTimeNumberLabel: UILabel!
//Buttons
#IBAction func startButton(_ sender: Any) {
Activate()
}
#IBAction func stopButton(_ sender: Any) {
Deactivate()
seconds = 59
minutes = 59
hours = 47
}
//Timer
var timer = Timer()
var seconds = 0
var minutes = 0
var hours = 0
// Nitifications
//END
override func viewDidLoad() {
super.viewDidLoad()
LoadApp()
// this enables notifications
UNUserNotificationCenter.current().requestAuthorization(options:[.alert , .sound , .badge], completionHandler:{ didAllow, error in
})
}
func Activate (){
if activated == false {
streakNumber += 1
}
activated = true
streakNumberLabel.text = String(streakNumber)
}
func Deactivate (){
if activated == true{
activated = false
ActivTimer()
// Notification
let content = UNMutableNotificationContent()
content.title = " 10 secodns are up "
content.subtitle = " yep time passed"
content.body = " The 10 seconds are really up!!"
content.badge = 1
let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 600, repeats:false)
let request = UNNotificationRequest(identifier: "timerDone", content: content , trigger: trigger)
UNUserNotificationCenter.current().add(request,withCompletionHandler:nil)
}
}
#objc func Clock(){
seconds = seconds-1
if seconds == -1{
seconds = 59
minutes = minutes-1
}
if minutes == -1{
minutes = 59
hours = hours-1
}
remainingTimeNumberLabel.text = (String(hours) + ":" + String(minutes) + ":" + String(seconds))
if seconds == 0 && hours == 0 && minutes == 0 {
timer.invalidate()
}
}
func ActivTimer(){
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ViewController.Clock), userInfo: nil, repeats: true)
}//SAVING STUFF DOESNT WORK
//
func SaveApp(){
streakNumberString = String(streakNumber)
defaults.set(streakNumberString, forKey: "streakNumbers")
print("Saved" + String(defaults.integer(forKey: "streakNumbers")))
}
func LoadApp(){
streakNumberString = defaults.string(forKey: "streakNumbers")!
print (defaults.integer(forKey: "streakNumbers") )
streakNumber = Int(streakNumberString)!
streakNumberLabel.text = String(streakNumber)
}//
}

Answer 1

The error says it all. You can't invoke SaveApp() on ViewController. You actually need an instance of the ViewController to invoke SaveApp() on itself.
If you wish your ViewController instance to save its data on App termination, you could post a Notification from the AppDelegate's applicationDidEnterBackground method, which is called whenever the app is being minimized and before termination as well:
func applicationDidEnterBackground(_ application: UIApplication) {
NotificationCenter.default.post(Notification(name: Notification.Name("AppAboutToTerminateOrMinimize")))
}
Then you could subscribe to that notification in your ViewController's viewDidLoad():
NotificationCenter.default.addObserver(self,
selector: #selector(AppSave),
name: Notification.Name("AppAboutToTerminateOrMinimize"),
object: nil)
Or as rmaddy mentioned in the comments, you can just put the below code in ViewController's viewDidLoad() and skip the AppDelegate part:
NotificationCenter.default.addObserver(self,
selector: #selector(AppSave),
name: Notification(name: UIApplicationDidEnterBackgroundNotification,
object: nil)
This way when the app minimizes/terminates the AppDelegate will send notification, the ViewController instance (if alive) will receive it and will call AppSave()
You'd have to annotate AppSave() method as #objc
And it's a good practice to use lowerCamelCase for naming of properties and methods /i.e appSave() instead of AppSave()