If I go to another view controller and return to the same one using a segue, does the snapshotListener reread all the documents? - swift

Question

This is a little snip it from my code.
db.collection("tasks").document(Auth.auth().currentUser?.uid ?? "").collection("currentUser").whereField("Date", isEqualTo: date).addSnapshotListener{ (querySnapshot, err) in
self.task = []
if querySnapshot!.documents.isEmpty{
self.firstView.alpha = 1
self.labelText.alpha = 1
}
else{
self.firstView.alpha = 0
self.labelText.alpha = 0
if let snapshotDocuments = querySnapshot?.documents{
for doc in snapshotDocuments{
let data = doc.data()
print("xx")
if let descS = data["Task Description"] as? String, let dateS = data["Date"] as? String, let titleS = data["Task Title"] as? String, let type1 = data["Type"] as? String{
let newTask = Tasks(title: titleS, desc: descS, date: dateS, type: type1, docId: doc.documentID)
self.task.append(newTask)
DispatchQueue.main.async {
self.taskTableView.reloadData()
let indexPath = IndexPath(row: self.task.count - 1, section: 0)
self.taskTableView.scrollToRow(at: indexPath, at: .top, animated: false)
}
}
}
}
}
}
The problem is that when I go to add another task I perform a segue to another view controller. From there I add a document but I need to perform another segue to go back because I am using a hamburger menu.
I did try using getDocuments(source: cache), which did reduce writes when the user did not add a task. But when they did add a task it reloads all the documents, adding tons of reads. The goal of using a snapshotListner is to reduce reads, however, I'm not sure if it will reread data when I perform a segue to the screen again. Thank-You!

Answer 1

The snapshot listener doesn't care at all about anything going on the UI, such as segues. The snapshot listener only fires when you first add it and when there are updates in the remote data. You can finetune the snapshot listener to omit or include cached or presumed data (using the snapshot's metadata property). But this is the nature of realtime data, it may get updated a lot as the user does things. The only workaround is coming up with the most efficient data architecture possible (on the server side) to reduce your read cost.
As an aside, your code is very dangerously written. You should first check if there is a valid userId before attaching a listener to a userId that even your code suggests could be an empty string. You should never force unwrap snapshots like you are doing because it will crash the entire app when there is even a slight network error.