CODEWITHSUNDEEP
iosfirebaseswift3firebase-realtime-database
mikew
mikew

Reputation: 377

Table view continues to add rows while observing .childAdded even when child was not added in Firebase

I have a UITableView that gets populated by the following firebase database:

"games" : {
    "user1" : {
      "game1" : {
        "currentGame" : "yes",
        "gameType" : "Solo",
        "opponent" : "Computer"
      }
    }
  }

I load all the games in viewDidLoad, a user can create a new game in another UIViewController, once a user does that and navigates back to the UITableView I want to update the table with the new row. I am trying to do that with the following code:

var firstTimeLoad : Bool = true
override func viewDidLoad() {
    super.viewDidLoad()
    if let currentUserID = Auth.auth().currentUser?.uid {
        let gamesRef = 
        Database.database().reference().child("games").child(currentUserID) 

        gamesRef.observe(.childAdded, with: { (snapshot) in
            let game = snapshot
            self.games.append(game)
            self.tableView.reloadData()
        })
    }
}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    if firstTimeLoad {
        firstTimeLoad = false
    } else {
        if let currentUserID = Auth.auth().currentUser?.uid {
            let gamesRef = Database.database().reference().child("games").child(currentUserID)
            gamesRef.observe(.childAdded, with: { (snapshot) in
                self.games.append(snapshot)
                self.tableView.reloadData()
            })
        }
    }
}

Lets say there is one current game in the data base, when viewDidLoad is run the table displays correctly with one row. However anytime I navigate to another view and navigate back, viewDidAppear is run and for some reason a duplicate game seems to be appended to the games even though no child is added.

The cells are being populated by the games array:

internal func tableView(_ tableView: UITableView, cellForRowAt indexPath: 
IndexPath) -> UITableViewCell {

    let cell = Bundle.main.loadNibNamed("GameTableViewCell", owner: 
    self, options: nil)?.first as! GameTableViewCell

    let game = games[indexPath.row]
    if let gameDict = game.value as? NSDictionary {
        cell.OpponentName.text = gameDict["opponent"] as? String
    }

    return cell
}

UPDATE:

Thanks to everyone for their answers! It seems like I misunderstood how firebase .childAdded was functioning and I appreciate all your answers trying to help me I think the easiest thing for my app would be to just pull all the data every time the view appears.

Upvotes: 0

Views: 336

Answers (3)

oneshot
oneshot

Reputation: 663

observe(.childAdded) is called at first once for each existing child, then one time for each child added. Since i also encounter a similar issue, assuming you don't want to display duplicate objects, in my opinion the best approach, which is still not listed in the answers up above, is to add an unique id to every object in the database, then, for each object retrieved by the observe(.childAdded) method, check if the array which contains all objects already contains one with that same id. If it already exists in the array, no need to append it and reload the TableView. Of course observe(.childAdded) must also be moved from viewDidLoad() to viewWillAppear(), where it belongs, and the observer must be removed in viewDidDisappear. To check if the array already includes that particular object retrieved, after casting snapshot you can use method yourArray.contains(where: {($0.id == retrievedObject.id)}).

Upvotes: 0

iOS Geek
iOS Geek

Reputation: 4855

Try following code and no need to check for bool , Avoid using bool here its all async methods , it created me an issue in between of my chat app when its database grows

//Remove ref in didLoad
//Remove datasource and delegate from your storyboard and assign it in code so tableView donates for data till your array don't contain any data
//create a global ref 
let gamesRef = Database.database().reference()

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

        self.games.removeAllObjects()
        if let currentUserID = Auth.auth().currentUser?.uid {
            gamesRef.child("games").child(currentUserID)observe(.childAdded, with: { (snapshot) in
                self.games.append(snapshot)
                self.tableView.dataSource = self
                self.tableView.delegate = self
                self.tableView.reloadData()
        })
            gamesRef.removeAllObserver() //will remove ref in disappear itself 
            //or you can use this linen DidDisappear as per requirement 
        }
        else{
           //Control if data not found
            }
        }

//TableView Delegate

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

            if self.games.count == 0{
                let emptyLabel = UILabel(frame: CGRect(x: 0, y: 0, width: self.view.bounds.size.width, height: self.view.bounds.size.height))
                emptyLabel.text = "No Data found yet"
                emptyLabel.textAlignment = .center
                self.tableView.backgroundView = emptyLabel
                self.tableView.separatorStyle = .none
                return 0
            }
            else{
                return self.games.count
            }
        }

Upvotes: 1

user8606263
user8606263

Reputation:

From what I can see, the problem here is that every time you push the view controller and go back to the previous one, it creates a new observer and you end up having many observers running at the same time, which is why your data appears to be duplicated.

What you need to do is inside your viewDidDisappear method, add a removeAllObservers to your gameRef like so :

override func viewDidDisappear(_ animated: Bool) {
   super.viewDidDisappear(animated)

   guard let currentUserId = Auth.auth().currentUser?.uid else {
      return
   }

   let gamesRef = Database.database().reference().child("games").child(currentUserId)

   gamesRef.removeAllObservers()

}

I cannot see all your code here so I am not sure what is happening, but before adding your child added observer, you need to remove all the elements from your array like so :

games.removeAll()

Actually, as per best practices, you should not call your method inside your ViewDidLoad, but instead you should add your observer inside the viewWillAppear method.

I cannot test your code right now but hopefully it should work like that! Let me know if it doesn't :)

UPDATE:

If you want to initially load all the data, and then pull only the new fresh data that is coming, you could use a combination of the observeSingleEvent(of: .value) and observe(.childAdded) observers like so :

var didFirstLoad = false

gamesRef.child(currentUserId).observe(.childAdded, with: { (snapshot) in

    if didFirstLoad {
       // add your object to the games array here
    }

}

gamesRef.child(currentUserId).observeSingleEvent(of: .value, with: { (snapshot) in

    // add the initial data to your games array here

    didFirstLoad = true
}

By doing so, the first time it loads the data, .childAdded will not be called because at that time didFirstLoad will be set to false. It will be called only after .observeSingleEvent got called, which is, by its nature, called only once.

Upvotes: 1

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