Completion handler Firebase observer in Swift - ios

Question

I am making a completion handler for a function which will return a list of objects. When it return value for first time, it works well. But when any change happen into firebase database and again observe gets called, array size gets doubled up. Why it's getting doubled up?
func getStadiums(complition: #escaping ([Stadium]) -> Void){
var stadiums: [Stadium] = []
let stadiumRef = Database.database().reference().child("Stadium")
stadiumRef.observe(.value, with: { (snapshot) in
for snap in snapshot.children {
guard let stadiumSnap = snap as? DataSnapshot else {
print("Something wrong with Firebase DataSnapshot")
complition(stadiums)
return
}
let stadium = Stadium(snap: stadiumSnap)
stadiums.append(stadium)
}
complition(stadiums)
})
}
And calling like this
getStadiums(){ stadiums
print(stadiums.count) // count gets doubled up after every observe call
}

Answer 1

The code you're using declares stadiums outside of the observer. This means any time a change is made to the value of the database reference, you're appending the data onto stadiums without clearing what was there before. Make sure to remove the data from stadiums before appending the snapshots again:
func getStadiums(complition: #escaping ([Stadium]) -> Void){
var stadiums: [Stadium] = []
let stadiumRef = Database.database().reference().child("Stadium")
stadiumRef.observe(.value, with: { (snapshot) in
stadiums.removeAll() // start with an empty array
for snap in snapshot.children {
guard let stadiumSnap = snap as? DataSnapshot else {
print("Something wrong with Firebase DataSnapshot")
complition(stadiums)
return
}
let stadium = Stadium(snap: stadiumSnap)
stadiums.append(stadium)
}
complition(stadiums)
})
}

Answer 2

This line stadiumRef.observe(.value, with: { (snapshot) in ... actually adding an observer that will be called everytime your stadium data is changed.
Because you called it twice by using getStadiums(){ stadiums ..., the total observer added will be 2.
That makes the line stadiums.append(stadium) called twice in the second call.
My suggestion would be to use stadiumRef.observe() once without calling it from getStadiums().

Answer 3

Create a Model as below
class OrderListModel: NSObject {
var Order:String?
var Date:String?
}
Use the below code in the view controller and you should be able to see content in your tableview
func getOrdersData() {
self.orderListArr.removeAll()
let ref = Database.database().reference().child(“users”).child(user).child("Orders")
ref.observe(.childAdded, with: { (snapshot) in
print(snapshot)
guard let dictionary = snapshot.value as? [String : AnyObject] else {
return
}
let orderObj = OrderModel()
orderObj.Order = dictionary[“Order”] as? String
orderObj.Date = dictionary[“Date”] as? String
self.orderListArr.append(orderObj)
self.tableView.delegate = self
self.tableView.dataSource = self
self.tableView.reloadData()
}, withCancel: nil)
}

Answer 4

func ListenForChildrenAdded() {
let registerToListenTo = "YourPathHere"
ref.child(registerToListenTo).observeSingleEvent(of: .value) { (snapshot) in
let initialChildren = snapshot.childrenCount
var incrementer = 0
ref.child(registerToListenTo).observe(.childAdded, with: { (snapshot) in
incrementer += 1
print("snapshot: \(snapshot.key) #\(incrementer)")
if incrementer == initialChildren {
print("-> All children found")
} else if incrementer > initialChildren {
print("-> Child Was Added - Run Some Code Here")
}
})
}}