How to perform an action only after data are downloaded from Firebase

Question

I\'m trying to figure out how to trigger an action only after the observeSingleEvent in Firebase has finished its work.

The reason behind is that I need to do the fo

Answer 1

Firebase is asynchronous so to make code execute in a defined order, you need to 'wait' for firebase to return data.

The closures that go with Firebase functions do just that - the code within the closure executes when the data (snapshot) is valid.

Move doSomethingHere() to within the Firebase closure and it will execute in the correct order - in this case

if listOfTags.count != 0 {
    for tag in listOfTags {

        ref.child("tags").child(tag).observeSingleEvent(of: .value, with: { (snapshot) in

            if let temp = snapshot.children.allObjects as? [FIRDataSnapshot] {
                for elem in temp {
                    outputArray.append(elem.key)
                }
                doSomethingHere() //array is populated at this point
            }
        })
    }
}

Note you can also remove this

if listOfTags.count != 0

as if listOfTags is 0, the for loop will not execute.