How do I observe if there is a change in my Firestore database, then notify and prompt the user to reload?

Question

Here is my ViewModel code which grabs data from firebase firestore:

    gettingData = true
        
        //read docs at path templeu
        print("<-- Getting restaurants from \(selectedCollege) database -->")
        db.collection(selectedCollege).addSnapshotListener({ [self] querySnapshot, error in
            guard let documents = querySnapshot?.documents else {
                print("no documents")
                return
            }
            
            self.restaurantList = documents.map { (queryDocumentSnapshot) -> Categories in
                let data = queryDocumentSnapshot.data()
                
                return Categories(
                    id: data["id"] as? String ?? UUID().uuidString,
                    name: data["name"] as? String ?? "[Name]",
                    type: data["type"] as? [String] ?? ["None"],
                    pic: data["pic"] as? String ?? "",
                    price: data["price"] as? String ?? "",
                    hours: data["hours"] as? [String:[String]] ?? ["Thursday": ["0.00", "0.00"]],
                    hoursString: data["hoursString"] as? String ?? "",
                    stars: data["stars"] as? String ?? "",
                    website: data["website"] as? String ?? "",
                    location: data["location"] as? String ?? "",
                    coordinates: data["coordinates"] as? [Double] ?? [0.0, 0.0],
                    phoneNumber: data["phoneNumber"] as? String ?? "1112223456",
                    currency: data["currency"] as? String ?? "[Currency]",
                    review: data["review"] as? [String] ?? ["Review"],
                    wait: data["wait"] as? String ?? "[Wait]",
                    campus: data["campus"] as? String ?? "[Campus]",
                    featured: data["featured"] as? Bool ?? false,
                    forceClose: data["forceClose"] as? Bool ?? false
                )
            }
            self.moodList = self.restaurantList
            print("<-- Done Getting Data -->")
            self.gettingData = false
        })

Currently, when I update something in the database, the user is forced out of whatever screen they were on as the data updates in my views. How do I detect when there is a change to my database, then notify the user of this and prompt them to refresh the data with a button that appears in a view?

Answer 1

You can make a closure and call it in viewDidLoad() function and when there is any change in Firestore, you can show the user an alert message if he wants to reload the interface or not.

show example:

class HomePageViewController: UIViewController {
    
    var restaurantList: [Category] = []
    var gettingData: Bool = true
    
    override func viewDidLoad() {
        super.viewDidLoad()

        self.setListnerCollectionOfCategories() { categories in
            
            let alert = UIAlertController(title: "New Data!!", message: "Are you sure want to refresh data?", preferredStyle: .alert)
            
            let ok = UIAlertAction(title: "Yes", style:
                UIAlertAction.Style.default) {
                   UIAlertAction in

                self.restaurantList = categories
                self.gettingData = true
                
                //MARK:- reload data

            }

            let cancel = UIAlertAction(title: "Cancel", style:
                UIAlertAction.Style.cancel) {
                   UIAlertAction in
                self.gettingData = true
            }
            
            alert.addAction(ok)
            alert.addAction(cancel)

            self.present(alert, animated: true, completion: nil)
            
        }
        
    }
    
    func setListnerCollectionOfCategories(completion: @escaping(([Category])->(Void))) {
        //read docs at path templeu
        print("<-- Getting restaurants from \(selectedCollege) database -->")
        db.collection(selectedCollege).addSnapshotListener({ [self] querySnapshot, error in
            guard let documents = querySnapshot?.documents else {
                print("no documents")
                return
            }
            
            var categories = [Category] = []
            categories = documents.map { (queryDocumentSnapshot) -> Categories in
                let data = queryDocumentSnapshot.data()
                
                return Categories(
                    id: data["id"] as? String ?? UUID().uuidString,
                    name: data["name"] as? String ?? "[Name]",
                    type: data["type"] as? [String] ?? ["None"],
                    pic: data["pic"] as? String ?? "",
                    price: data["price"] as? String ?? "",
                    hours: data["hours"] as? [String:[String]] ?? ["Thursday": ["0.00", "0.00"]],
                    hoursString: data["hoursString"] as? String ?? "",
                    stars: data["stars"] as? String ?? "",
                    website: data["website"] as? String ?? "",
                    location: data["location"] as? String ?? "",
                    coordinates: data["coordinates"] as? [Double] ?? [0.0, 0.0],
                    phoneNumber: data["phoneNumber"] as? String ?? "1112223456",
                    currency: data["currency"] as? String ?? "[Currency]",
                    review: data["review"] as? [String] ?? ["Review"],
                    wait: data["wait"] as? String ?? "[Wait]",
                    campus: data["campus"] as? String ?? "[Campus]",
                    featured: data["featured"] as? Bool ?? false,
                    forceClose: data["forceClose"] as? Bool ?? false
                )
            }
            print("<-- Done Getting Data -->")
            self.gettingData = false
            completion(categories)
            
        })

    }
            
}