Removing Firestore SnapshotListener - swift

Question

I am currently working on a valet app. I have two table views one for the Location of the worker, and then another that when you click on a location the cars that are under that location come up in the new tableview.
My current problem is that when I click on a new location the old snapshot listener is still on and if an update happens under that location the second table view changes back to the original location.
I tried to do what they say by removing listener but then it just doesn't work at all.
This is my code below
// func to select the individual row
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
switch tableView {
case SelectLocationTableView:
do {
if (allowed == false){ // postin data in table already but not reloading the page yet
Authenticate(title: "hi", message: "hi")
Location = postData[indexPath.row]
oldLocation=Location
}
}
do {
if (allowed == true) {
allowed = false
Location = postData[indexPath.row]
CarsRequestedTableView.reloadData()
DisplayLocations()
}
}
case CarsRequestedTableView:
CarSelected = postCars[indexPath.row]
WorkWithCar()
default:
print(Error.self)
}
}
// function to pull the location based on the cell you click on
func DisplayLocations (){
let listener = db.collection("Requested").document(Location).collection("Requested").addSnapshotListener { querySnapshot, error in
guard (querySnapshot?.documents) != nil else {
print("Error fetching documents: \(error!)")
return
}
self.postCars.removeAll()
for document in querySnapshot!.documents {
let post = document.documentID
self.postCars.append(post)
self.CarsRequestedTableView.reloadData()
self.DisplayAlert(title: "NEW REQUEST!", message: "CHECK FOR NEW REQUEST!")
}
}
}

Answer 1

You need to keep the listener registration in a (private) instance variable in your table view controller, and call its remove() method when you're ready to stop listening. The Firebase iOS Quickstart repo has a couple of classes that show how to do this, here is an example I took from RestaurantsTableViewController:
class RestaurantsTableViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
// ...
// the data that's displayed in the table view
private var restaurants: [Restaurant] = []
private var documents: [DocumentSnapshot] = []
// this method removes any existing listener and sets up a new query
fileprivate var query: Query? {
didSet {
if let listener = listener {
listener.remove()
observeQuery()
}
}
}
// this is where you keep the listener registration
private var listener: ListenerRegistration?
// set up the new snapshot listener and map documents to data
fileprivate func observeQuery() {
guard let query = query else { return }
stopObserving()
// Display data from Firestore, part one
listener = query.addSnapshotListener { [unowned self] (snapshot, error) in
guard let snapshot = snapshot else {
print("Error fetching snapshot results: \(error!)")
return
}
let models = snapshot.documents.map { (document) -> Restaurant in
let maybeModel: Restaurant?
do {
maybeModel = try document.data(as: Restaurant.self)
} catch {
fatalError("Unable to initialize type \(Restaurant.self) with dictionary \(document.data()): \(error)")
}
if let model = maybeModel {
return model
} else {
// Don't use fatalError here in a real app.
fatalError("Missing document of type \(Restaurant.self) at \(document.reference.path)")
}
}
self.restaurants = models
self.documents = snapshot.documents
if self.documents.count > 0 {
self.tableView.backgroundView = nil
} else {
self.tableView.backgroundView = self.backgroundView
}
self.tableView.reloadData()
}
}
// this is where you stop the listener
fileprivate func stopObserving() {
listener?.remove()
}
/// ...
}