@obj protocol delegate method not working in second class. Swift

Question

Im trying to call protocol delegate in an additional class. The first class (ViewController) works but the second one I have implemented it in doesn't show any data. I added it with the autofill option so its not giving errors. It just doesn't do anything.

sender class

@objc protocol BWWalkthroughViewControllerDelegate{

  @objc optional func walkthroughPageDidChange(pageNumber:Int)     // Called when current page changes

}

@objc class BWWalkthroughViewController: UIViewController, UIScrollViewDelegate, ViewControllerDelegate {

  // MARK: - Public properties -

  weak var delegate:BWWalkthroughViewControllerDelegate?


  var currentPage:Int{    // The index of the current page (readonly)
    get{
      let page = Int((scrollview.contentOffset.x / view.bounds.size.width))
      return page
    }
  }


  // MARK: - Private properties -

  let scrollview:UIScrollView!
  var controllers:[UIViewController]!
  var lastViewConstraint:NSArray?
  var shouldCancelTimer = false
  var aSound: AVAudioPlayer!
  var isForSound: AVAudioPlayer!
  var alligatorSound: AVAudioPlayer!
  var audioPlayer = AVAudioPlayer?()
  var error : NSError?
  var soundTrack2 = AVAudioPlayer?()
  let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
  var audioPlayerAnimalSound = AVAudioPlayer?()
  var audioPlayerAlphabetSound = AVAudioPlayer?()
  var audioPlayerFullPhraze = AVAudioPlayer?()
  var audioPlayerPhonics = AVAudioPlayer?()

Code removed to save space carries on:

  /**
  Update the UI to reflect the current walkthrough situation
  **/

  private func updateUI(){

    // Get the current page

    pageControl?.currentPage = currentPage


    // Notify delegate about the new page

    delegate?.walkthroughPageDidChange?(currentPage)

  } 

receiver class

class BWWalkthroughPageViewController: UIViewController, BWWalkthroughPage, ViewControllerDelegate, BWWalkthroughViewControllerDelegate {

Function in second Class.

func walkthroughPageDidChange(pageNumber: Int) {
    println("current page 2 \(pageNumber)")

  }

walkthroughPageDidChange does work in the viewController class however. Please can you help me see what is wrong?

Answer 1

Your weak var delegate:BWWalkthroughViewControllerDelegate? is an optional variable and it is not assigned anywhere in your presented code, hence it will be nil. You have to instantiate it somewhere for it to work.

A good way to do so is:

class BWWalkthroughViewController {
    let bwWalkthroughPageViewController = BWWalkthroughPageViewController()
    var bwWalkthroughViewControllerDelegate : BWWalkthroughViewControllerDelegate!

    init() {
        bwWalkthroughViewControllerDelegate = bwWalkthroughPageViewController as BWWalkthroughViewControllerDelegate
    }
}

A thing to note is that it is often good practice to name the delegates with meaningful names. The keyword "delegate" is often used for many classes and is restricted. A more verbose name will eliminate the chance of overriding an original delegate and will help identify each one if you have more than one.