swift - Cant find in stack work answer on: How to know when Firebase retrieved data

Question

please explain where (method or maybe exists observe with competition method) I need retrieve data from Firebase. What is best practices?

    var ref:FIRDatabaseReference!

    ref = FIRDatabase.database().reference()

    //filling ShopList by favorite
    ref.child("goods").observeSingleEvent(of:.value, with: {(snapshot) in
        if let snapshots = snapshot.children.allObjects as? [FIRDataSnapshot] {

            print("my app: 1. Start ObserveSingle")

            for snap in snapshots {

                let g = Good()
                g.barcode = String(describing: snap.childSnapshot(forPath: "barcode").value!)
                g.name = snap.childSnapshot(forPath: "name").value! as! String
                g.price = snap.childSnapshot(forPath: "minprice").value! as! Double
                g.favorite = snap.childSnapshot(forPath: "favorite").value! as! Bool

                if g.favorite {//избранные товары
                    DataService.dataService.dbShopList.append(g)
                }
            }

            print("my app: 2. Observe finished (DataService.dataService.dbShopList.count)")
        }

    })

    print("my app: 3. observe finished (DataService.dataService.dbShopList.count)")

How to understand when and where finished step 2

Debug below

    my app: 3. observe finished 0
    my app: 1. Start ObserveSingle
    my app: 2. Observe finished 3

Answer 1

Waitting for answers