Why are previous views that have been popped from the stack still active - ios

Question

I have this truck driving app in swiftUI where I use fire base to log users in and out. The problem is that when I sign in with one user, and all it’s fire base functionalities are triggered, After I log out from the current user and into a new user, the functionality of the old user is still playing out. I think it might have something to do with the firebase functions being in an onAppear method. I am not sure though.
This is the firebase code. I dont think what Im querying has any relation to the solution so I wont explain it but if you think it does than please let me know.
.onAppear(perform: {
UNUserNotificationCenter.current().requestAuthorization(options: [.alert,.sound,.badge]) { (_,_) in
}
myDrivers = []
getEmails()
db.collectionGroup("resources").whereField("control", isEqualTo: true).addSnapshotListener { (snapshot, err) in
if myDrivers.count == 0{}
else{
if err != nil{print("Error fetching motion status: \(err)")}
if ((snapshot?.documents.isEmpty) != nil){}
// Gets all the driverLocation documents
for doc in snapshot!.documents{
if myDrivers.contains(doc.reference.parent.parent!.documentID){
let isDriving = doc.get("isDriving") as! Bool
let isStopped = doc.get("isStopped") as! Bool
let notified = doc.get("notified") as! Bool
if (isDriving == false && isStopped == false) || notified{}
else{
// Gets the name of the drivers
doc.reference.parent.parent?.getDocument(completion: { (snapshot, err) in
if err != nil{print("Error parsing driver name: \(err)")}
let firstName = snapshot?.get("firstName") as! String
let lastName = snapshot?.get("lastName") as! String
self.notifiedDriver = "\(firstName) \(lastName)"
})
// Logic
if isDriving{
send(notiTitle: "MyFleet", notiBody: "\(notifiedDriver) is back on the road.")
showDrivingToast.toggle()
doc.reference.updateData(["notified" : true])
}else if isStopped{
send(notiTitle: "MyFleet", notiBody: "\(notifiedDriver) has stopped driving.")
showStoppedToast.toggle()
doc.reference.updateData(["notified" : true])
}
}
}
else{}
}
}
}
})

Answer 1

Listeners don't die when a view controller is left. They remain active.
It's important to manage them through handlers for specific listeners as a view closes or the user navigates away. Here's how to remove a specific listener
let listener = db.collection("cities").addSnapshotListener { querySnapshot, error in
// ...
}
and then later
// Stop listening to changes
listener.remove()
Or, if your user is logging out, you can use removeAllObservers (for the RealtimeDatabase) to remove them all at one time, noting that
removeAllObservers must be called again for each child reference where
a listener was established
For Firestore, store the listeners in a listener array class var and when you want to remove them all, just iterate over the array elements calling .remove() on each.
There's additional info in the Firebase Getting Started Guide Detach Listener