Firebase removeAllObservers() keeps making calls when switching views -Swift2 iOS

Question

I read other stack overflow q&a's about this problem but it seems to be a tabBarController issue which I haven't found anything on.

I have a tabBarController with 3 tabs. tab1 is where I successfully send the info to Firebase. In tab2 I have tableView which successfully reads the data from tab1.

In tab2 my listener is in viewWillAppear. I remove the listener in viewDidDisappear (I also tried viewWillDisappear) and somewhere in here is where the problem is occurring.

override func viewDidDisappear(animated: Bool) {
    self.sneakersRef!.removeAllObservers()
    //When I tried using a handle in viewWillAppear and then using the handle to remove the observer it didn't work here either
    //sneakersRef!.removeObserverWithHandle(self.handle)
   }

Once I switch from tab2 to any other tab, the second I go back to tab2 the table data doubles, then if I switch tabs again and come back it triples etc. I tried setting the listener inside viewDidLoad which prevents the table data from duplicating when I switch tabs but when I send new info from tab1 the information never gets updated in tab2.

According to the Firebase docs and pretty much everything else I read on stackoverflow/google the listener should be set in viewWillAppear and removed in viewDidDisappear.

Any ideas on how to prevent my data from duplicating whenever I switch between back forth between tabs?

tab1

import UIKit
import Firebase
import FirebaseAuth
import FirebaseDatabase

class TabOneController: UIViewController{

var ref:FIRDatabaseReference!
@IBOutlet weak var sneakerNameTextField: UITextField!

override func viewDidLoad() {
      super.viewDidLoad()
      self.ref = FIRDatabase.database().reference()
}

@IBAction func sendButton(sender: UIButton) {

      let dict = ["sneakerName":self.sneakerNameTextField.text!]

      let usersRef = self.ref.child("users")
      let sneakersRef = usersRef.child("sneakers").childByAutoID()

      sneakersRef?.updateChildValues(dict, withCompletionBlock: {(error, user) in
                if error != nil{
                    print("\n\(error?.localizedDescription)")
                }
            })
      }
}

tab2

import UIKit
import Firebase
import FirebaseAuth
import FirebaseDatabase

class TabTwoController: UITableViewController{

@IBOutlet weak var tableView: UITableView!

var handle: Uint!//If you read the comments I tried using this but nahhh didn't help
var ref: FIRDatabaseReference!
var sneakersRef: FIRDatabaseReference?
var sneakerArray = [String]()

override func viewDidLoad() {
      super.viewDidLoad()
      self.ref = FIRDatabase.database().reference()
    }

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

      let usersRef = self.ref.child("users")
      //Listener
      self.sneakersRef = usersRef.child("sneakers")

      //I tried using the handle
      //---self.handle = self.sneakersRef!.observeEventType(.ChildAdded...

      self.sneakersRef!.observeEventType(.ChildAdded, withBlock: {(snapshot) in

      if let dict = snapshot.value as? [String:AnyObject]{

        let sneakerName = dict["sneakerName"] as? String
        self.sneakerArray.append(sneakerName)

        dispatch_async(dispatch_get_main_queue(), {
                self.tableView.reloadData()
       })

     }

   }), withCancelBlock: nil)
 }

//I also tried viewWillDisappear
override func viewDidDisappear(animated: Bool) {

        self.sneakersRef!.removeAllObservers()

        //When I tried using the handle to remove the observer it didn't work either
        //---sneakersRef!.removeObserverWithHandle(self.handle)
   }


func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
      return self.sneakerArray.count
  }

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
      let cell = self.tableView.dequeueReusableCellWithIdentifier("sneakerCell", forIndexPath: indexPath)
      cell.textLabel?.text = sneakerArray[indexPath.row]
      return cell
  }
}

tab3 does nothing. I just use it as an alternate tab to switch back and forth with

Answer 1

The official accepted Answer was posted by @vzsg. I'm just detailing it for the next person who runs into this issue. Up vote his answer.

What basically happens is when you use .childAdded, Firebase loops around and grabs each child from the node (in my case the node is "sneakersRef"). Firebase grabs the data, adds it to the array (in my case self.sneakerArray), then goes goes back to get the next set of data, adds it to the array etc. By clearing the array on the start of the next loop, the array will be empty once FB is done. If you switch scenes, you'll always have an empty array and the only data the ui will display is FB looping the node all over again.

Also I got rid of the dispatch_async call because he said FB calls the function in the main queue. I only used self.tableView.reloadData()

On a side note you should subscribe to firebase-community.slack.com. That's the official Firebase slack channel and that's where I posted this question and vzsg answered it.

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

  //CLEAR THE ARRAY DATA HERE before you make your Firebase query
  self.sneakerArray.removeAll()

  let usersRef = self.ref.child("users")
  //Listener
  self.sneakersRef = usersRef.child("sneakers")

  //I tried using the handle
  //---self.handle = self.sneakersRef!.observeEventType(.ChildAdded...

  self.sneakersRef!.observeEventType(.ChildAdded, withBlock: {(snapshot) in

  if let dict = snapshot.value as? [String:AnyObject]{

    let sneakerName = dict["sneakerName"] as? String
    self.sneakerArray.append(sneakerName)

    //I didn't have to use the dispatch_async here
    self.tableView.reloadData()

  }
 }), withCancelBlock: nil)
}

Answer 2

The removeAllObservers method is working correctly. The problem you're currently experiencing is caused by a minor missing detail: you never clear the contents of sneakerArray.

---

Note: there's no need for dispatch_async inside the event callback. The Firebase SDK calls this function on the main queue.

Answer 3

Thank for asking this question.

I have also faced same issue in past. I have solved this issue as follow.

1) Define array which contain list of observer.

var aryObserver = Array<Firebase>()

2) Add observer as follow.

 self.sneakersRef = usersRef.child("sneakers")
 aryObserver.append( self.sneakersRef)

3) Remove observer as follow.

  for fireBaseRef in self.aryObserver{
            fireBaseRef.removeAllObservers()
        }

 self.aryObserver.removeAll() //Remove all object from array.