How to pass array of data between UIViewControllers from @objc function

Question

I have a Child UICollectionViewController where I have an array of images. When I delete any photo I want to send back that array of updated images to Parent UIViewController . Also in Child controller I have a programatically view which is called when I click on any image to expand it. When the image is expanded the user can click on a Delete button to delete photos from that array. My array is updated correctly after delete but I can't manage to send it back to parent for some reasons. I tried to send it back using Delegates and Protocols. Here is my code for child controller:

protocol ListImagesDelegate {

    func receiveImagesUpdated(data: [String]?)
}

class ListImagesVC: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {

// Properties
    var receivedImagesPath: [String]? = []
    var fullscreenImageView = UIImageView()
    var indexOfSelectedImage = 0
    var imagesAfterDelete: [String]? = []
    var delegate: ListImagesDefectDelegate?


override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)

        print("imagesAfterDelete: \(imagesAfterDelete ?? [])") // I'm getting the right number of images in this array.

        delegate?.receiveImagesUpdated(data: imagesAfterDelete)
    }


...
...

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

        print("Click on photo: \(indexPath.item + 1)")

        if let imagePath = receivedImagesPath?[indexPath.item] {

            guard let selectedImage = loadImageFromDiskWith(fileName: imagePath) else {return}

            setupFullscreenImageView(image: selectedImage)

            indexOfSelectedImage = indexPath.item
        }
    }

    private func setupFullscreenImageView(image: UIImage){

        fullscreenImageView = UIImageView(image: image)
        fullscreenImageView.frame = UIScreen.main.bounds
        fullscreenImageView.backgroundColor = .black
        fullscreenImageView.contentMode = .scaleAspectFit
        fullscreenImageView.isUserInteractionEnabled = true

        self.view.addSubview(fullscreenImageView)
        self.navigationController?.isNavigationBarHidden = true
        self.tabBarController?.tabBar.isHidden = true

        let deleteButton = UIButton(frame: CGRect(x: fullscreenImageView.bounds.maxX - 50, y: fullscreenImageView.bounds.maxY - 75, width: 30, height: 40))
        deleteButton.autoresizingMask = [.flexibleLeftMargin, .flexibleBottomMargin]
        deleteButton.backgroundColor = .black
        deleteButton.setImage(UIImage(named: "trashIcon"), for: .normal)
        deleteButton.addTarget(self, action: #selector(deleteButtonTapped), for: .touchUpInside)

        fullscreenImageView.addSubview(deleteButton)
    }

    @objc func deleteButtonTapped(button: UIButton!) {
        print("Delete button tapped")

        receivedImagesPath?.remove(at: indexOfSelectedImage)

        imagesAfterDelete = receivedImagesPath

        collectionView.reloadData()

        self.navigationController?.isNavigationBarHidden = false
        self.tabBarController?.tabBar.isHidden = false
        fullscreenImageView.removeFromSuperview()
    }

Here is the Parent controller:

var updatedImages: [String]? = []

...
...

extension NewAlbumVC: ListImagesDelegate {

    func receiveImagesUpdated(data: [String]?) {

        print("New array: \(data ?? [])") // This print is never called.

        updatedImages = data

    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

        if segue.identifier == "goToImages" {

            let listImagesVC = segue.destination as! ListImagesVC

            listImagesVC.delegate = self
        }
    }
}

I want to specify that my child controller have set a Storyboard ID ( "ListImagesID" ) and also a segue identifier from parent to child ( "goToImages" ). Can cause this any conflict ?

Thanks if you read this.

Answer 1

It appears that the delegate is nil here

delegate?.receiveImagesUpdated(data: imagesAfterDelete)

For this

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

to trigger you must have

self.performSegue(withIdentifier:"goToImages",sender:nil)

---

Edit: This

let listImagesDefectVC = storyboard?.instantiateViewController(withIdentifier: "ListImagesDefectID") as!     ListImagesDefectVC
listImagesDefectVC.receivedImagesPath = imagesPath   
navigationController?.pushViewController(listImagesDefectVC, animated: true) 

doesn't trigger prepareForSegue , so add

listImagesDefectV.delegate = self

So finally

Solution 1 :

@objc func tapOnImageView() { 
     let listImagesDefectVC = storyboard?.instantiateViewController(withIdentifier: "ListImagesDefectID") as! ListImagesDefectVC
     listImagesDefectVC.receivedImagesPath = imagesPath 
     listImagesDefectVC.delegate = self
     navigationController?.pushViewController(listImagesDefectVC, animated: true)
 }

Solution 2 :

 @objc func tapOnImageView() {  
     self.performSegue(withIdentifier:"goToImages",sender:nil) 
 }

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    if segue.identifier == "goToImages" {

        let listImagesVC = segue.destination as! ListImagesVC
        listImagesVC.receivedImagesPath = imagesPath 
        listImagesVC.delegate = self
    }
}