Firebase removing observers - ios

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.

Answer 3

Observers must be removed on the same reference path they were put upon. And for the same number of times they were issued, or use ref.removeAllObservers() for each path.
Here's a trick I use, to keep it tidy:
var fbObserverRefs = [FIRDatabaseReference]() // keep track of where observers defined.
...then, put observers in viewDidLoad():
fbObserverRefs.append(ref.child("user/\(uid)"))
fbObserverRefs.last!.observe(.value, with: { snap in
// do the work...
})
...then, in viewWillDisappear(), take care of removing any issued observers:
// Only true when popped from the Nav Controller stack, ignoring pushes of
// controllers on top.
if isBeingDismissed || isMovingFromParentViewController {
fbObserverRefs.forEach({ $0.removeAllObservers() })
}