Firebase removing observers

Question

I have a problem removing a Firebase observer in my code. Here's a breakdown of the structure:

var ref = Firebase(url:"https://MY-APP.firebaseio.com/")
var handle = UInt?

override func viewDidLoad() {
    handle = ref.observeEventType(.ChildChanged, withBlock: {
        snapshot in

        //Do something with the data
    }
}

override func viewWillDisappear(animated: Bool) {
    if handle != nil {
        println("Removed the handle")
        ref.removeObserverWithHandle(handle!)
    }
}

Now when I leave the viewcontroller, I see that "Removed the handle" is printed, but when I return to the viewcontroller, my observer is called twice for each event. When I leave and return again, it's called three times. Etc. Why is the observer not being removed?

I do also call ref.setValue("some value") later in the code, could this have anything to do with it?

Answer 1

Thought I was having this bug but in reality I was trying to remove observers on the wrong reference.

ORIGINAL CODE:

let ref: FIRDatabaseReference = FIRDatabase.database().reference()
var childAddedHandles: [String:FIRDatabaseHandle] = [:]

func observeFeedbackForUser(userId: String) {
    if childAddedHandles[userId] == nil { // Check if observer already exists

        // NOTE: - Error is caused because I add .child(userId) to my reference and
        //     do not when I call to remove the observer.

        childAddedHandles[userId] = ref.child(userId).observeEventType(.ChildAdded) { 
            [weak self] (snapshot: FIRDataSnapshot) in

            if let post = snapshot.value as? [String:AnyObject],
               let likes = post["likes"] as? Int where likes > 0 {             

                self?.receivedFeedback(snapshot.key, forUserId: userId)          
            }
        }
    }
}

func stopObservingUser(userId: String) {
    // THIS DOES NOT WORK

    guard let cah = childAddedHandles.removeValueForKey(userId) else {
        print("Not observing user")
        return
    }

    // Error! I did not add .child(userId) to my reference
    ref.removeObserverWithHandle(cah)
}

FIXED CODE:

func stopObservingUser(userId: String) {
    // THIS WORKS

    guard let cah = childAddedHandles.removeValueForKey(userId) else {
        print("Not observing user")
        return
    }

    // Add .child(userId) here
    ref.child(userId).removeObserverWithHandle(cah)
}

Answer 2

Given it's April 2015 and the bug is still around I'd propose a workaround for the issue:

• keep a reference of the handles (let's say in a dictionary and before initiating a new observer for the same event type check if the observer is already there.

Having the handles around has very low footprint (based on some official comments :) ) so it will not hurt that much.