Realtime update array from Firestore - swift

Question

I am trying to download information from a Firebase Firestore document that is then appended to an array in realtime. Everytime I add a document, delete or edit a document I would like the app to update and sync the array to match the data. I was able to retrieve the data with the following code:
database.collection("_Products").getDocuments(completion: { (snapshot, error) in
if error != nil {
print(error as Any)
}else{
for document in (snapshot?.documents)! {
let Name = document.data()["Item Name"] as! String
let Price = document.data()["Item Price"] as! String
let Number = document.data()["Item Number"] as! String
let Brand = document.data()["Item Brand"] as! String
let Quantity = document.data()["Quantity"] as! String
let Category = document.data()["Item Category"] as! String
DispatchQueue.main.async {
if instoreCheckOutArray.contains(where: {$0.Number == Number && $0.Brand == Brand}){
return
}else{
instoreCheckOutArray.append(checkOutArrayInfo(Brand: Brand, Name: Name, Number: Number, Price: Price, Quantity: Quantity, Category: Category))
self.searchForCoupon()
}
}
}
}
})
I then use the following code to run the function every second to fetch the data from the database:
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(updateCart), userInfo: nil, repeats: true)
Running the previous code perfectly fetches me new data but I cannot get the app to update the existing array to match the database and when I remove a document from the database it stays in the array.
Thank you in advanced.

Answer 1

1.Declare scrollingTimer variable
var scrollingTimer = Timer()
2.Initialize scrollingTimer with your function
scrollingTimer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(updateCart), userInfo: nil, repeats: true)
3.Fire the scrollingTimer(fire any where you want)
scrollingTimer.fire()
To stop the scrolling timer use the below line(Stop any where you want)
scrollingTimer.invalidate()
If any Please refer the link (DevelopersDocument)