Detach from Firestore listener - ios

Question

I'm using Firestore together with Swift.
I have a singleton data class UserManager. I call this from my different ViewControllers to get data to populate my tableviews. I want the tableviews to automatically update when the collections are updated so I need to use a SnapshotListener. Everything works fine but I'm not sure how to detach from the listener when the Viewcontroller is closed.
In the singleton class I have methods like this below. The method gives a list of users and will be called from several different places around my app.
I also want to give back a reference to the listener so that I can detach from it when the Viewcontroller is closed. But I can't get it working. The below solution gives compiler error.
I've been trying to look at the reference, for example here
https://firebase.google.com/docs/firestore/query-data/listen but I need to get it working when the data is loaded in a singleton class instead of directly in the Viewcontroller. What is the way to go here?
In UserManager:
func allUsers(completion:#escaping ([User], ListenerRegistration?)->Void) {
let listener = db.collection("users").addSnapshotListener { querySnapshot, error in
if let documents = querySnapshot?.documents {
var users = [User]()
for document in documents {
let user = User(snapshot: document)
users.append(user)
}
completion(users, listener)
}
}
}
In ViewController:
override func viewDidLoad() {
super.viewDidLoad()
UserManager.shared.allUsers(completion: { (users, listener) in
self.users = users
self.listener = listener
self.tableView.reloadData()
})
}
deinit {
self.listener.remove()
}

Answer 1

I guess the compiler error that you see is referring to the fact that you are using listener into it's own defining context.
Try this for a change:
In UserManager:
func allUsers(completion:#escaping ([User])->Void) -> ListenerRegistration? {
return db.collection("users").addSnapshotListener { querySnapshot, error in
if let documents = querySnapshot?.documents {
var users = [User]()
for document in documents {
let user = User(snapshot: document)
users.append(user)
}
completion(users)
}
}
}
In ViewController:
override func viewDidLoad() {
super.viewDidLoad()
self.listener = UserManager.shared.allUsers(completion: { (users) in
self.users = users
self.tableView.reloadData()
})
}
deinit {
self.listener.remove()
}

Answer 2

I think that getDocument instead of addSnapshotListener is what you are looking for.
Using this method the listener is automatically detached at the end of the request...
It will be something similar to
func allUsers(completion:#escaping ([User])->Void) {
db.collection("users").getDocument { querySnapshot, error in
if let documents = querySnapshot?.documents {
var users = [User]()
for document in documents {
let user = User(snapshot: document)
users.append(user)
}
completion(users)
}
} }