Using Firebase references in a UIViewController / from https://www.firebase.com/blog/2015-10-15-best-practices-uiviewcontroller-ios-firebase.html

MyViewController.swift

import UIKit

class MyViewController: UIViewController {
  
  // Store ref and handle as implicitly unwrapped optionals
  // explanation about this > because the initializer might not be called esp from the storyboard
  var ref: Firebase!
  
  var handle: UInt!
  
  override func viewDidLoad() {
    super.viewDidLoad()
    // Initialize Reference
    ref = Firebase(url: "https://<YOUR-FIREBASE-APP>.firebaseio.com/")
  }
  
  override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
    // Create listener and store handle
    handle = ref.observeEventType(.Value) { print($0) }
  }
  
  override func viewDidDisappear(animated: Bool) {
    super.viewDidDisappear(animated)
    // Remove listener with handle
    ref.removeObserverWithHandle(handle)
  }
}