Change value when view is dismissed

Question

I have a NowPlayingVC, as a child of my MainVC(a collection view), I'd like to change a textValue inside the NowPlayingVC when a third viewcontroller (SingleSoundVC) get dismissed. I do everything via code, and I cant understand why my labels are still not visible after the dismiss. If I try hard coding they work just fine, but never change.

I can print correctly when the third views gets dismissed but the label is empty, even though I can see it with the debug view hierarchy.

I tried with Protocol/Delegate like this:

Protocol

protocol SendDataToAudioPlayerContainer {
func receiveData(data:Sound){
     self.audioNameLabel.text = data.name
   }
}

NowPlayingVC

NowPlayingVC: SendDataToAudioPlayerContainer
     var audioNameLabel:UILabel = {
        var lbl = UILabel()
        lbl.numberOfLines = 0
        lbl.textAlignment = .left
        lbl.sizeToFit()
        lbl.textColor = .black
        return lbl
    } 
    override func viewDidLoad() {
        super.viewDidLoad()
        setupViews()
        setupConstraints()
    }
  func setupViews() {
    self.view.backgroundColor = .blue
    self.view.addSubview(audioNameLabel)
}
 func setupConstraints(){ //setup of constraints with SnapKit}

}

SingleSoundVC

var delegate:SendDataToAudioPlayerContainer?
var singleSound: Sound?
@objc func dismissView(){

    if self.delegate != nil {
        print("data passed up")
        let data = self.singleSound
        delegate?.receiveData(data: data!)
        self.dismiss(animated: true, completion: nil)

    } else {self.dismiss(animated: true, completion: nil)
        print("data is not passed")}

}

I also have to add that when I select the item I added NowPlaying as the delegate of MainVC

MainVC - CollectionView

  func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {

    let vc = MainVC()
    let childVC = NowPlayingVC()
    vc.delegate = childVC
    ApiService.sharedInstance.downloadAudioFile(with: vc.singleSound!.audioId)
    vc.modalPresentationStyle = .popover
    present(vc, animated: true, completion: nil)
}

Answer 1

MainVC - CollectionView

you should create a property for NowPlayingVC to reference to the same instance: var nowPlayingVC = NowPlayingVC()

  func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {

    let vc = SingleSoundVC()
    vc.delegate = nowPlayingVC
    ApiService.sharedInstance.downloadAudioFile(with: vc.singleSound!.audioId)
    vc.modalPresentationStyle = .popover
    present(vc, animated: true, completion: nil)
}

Protocol

should be defined as:

    protocol SendDataToAudioPlayerContainer {
        func receiveData(data:Sound)
    }

NowPlayingVC

adopt it to SendDataToAudioPlayerContainer protocol : add

func receiveData(data:Sound){
         self.audioNameLabel.text = data.name
         **// update constraints here**
       }
    }