Xcodeでコレクションビューを使ったTODOアプリを作っています。
collectionViewのセルをロングタップすると入力画面に遷移し、次画面にて入力された内容をセル上のラベルにそれぞれ表示したいのですが値が渡らず困っています・・・。
NavigationControllerは使っておらず、segueにはpresentModallyを使っています。エラー等も出ていません。
何か解る方がいましたらご教授お願いしたいです。よろしくお願いします。


import UIKit

struct MyTodoItem {
    var title: String
    var dateString: String? 
}


class ViewController: UIViewController,UICollectionViewDelegate,UICollectionViewDataSource,UIGestureRecognizerDelegate,nextViewControllerDelegate {



    @IBOutlet weak var todoCollection: UICollectionView!

    let toDos = ["1","2","3","4","5","6"]

    var todos: [MyTodoItem] = [
        MyTodoItem(title: "1", dateString: nil),
        MyTodoItem(title: "2", dateString: nil),
        MyTodoItem(title: "3", dateString: nil),
        MyTodoItem(title: "4", dateString: nil),
        MyTodoItem(title: "5", dateString: nil),
        MyTodoItem(title: "6", dateString: nil),
    ]




    override func viewDidLoad() {
        super.viewDidLoad()

        let layout = UICollectionViewFlowLayout()
        layout.sectionInset = UIEdgeInsets(top: 20, left: 20, bottom: 20, right: 20)
        layout.itemSize = CGSize(width: 100,height: 100)
        todoCollection.collectionViewLayout = layout

        let longPressGestureRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(cellLongPressed))
        longPressGestureRecognizer.delegate = self
        longPressGestureRecognizer.allowableMovement = 15
        longPressGestureRecognizer.minimumPressDuration = 0.6
        todoCollection.addGestureRecognizer(longPressGestureRecognizer)

    }


    func nextViewController(_ nextVC: NextViewController, didFinishText text: String?) {

       if let editingItem = self.editingItem {

                 todos[editingItem].dateString = text

                   todoCollection.reloadItems(at: [IndexPath(item: editingItem, section: 0)])
               }


    }



    //表示するセルの数
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 6
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
        cell.backgroundColor = .systemPink

        let item = todos[indexPath.row]


        let todoLabel = cell.contentView.viewWithTag(1) as! UILabel
        todoLabel.text = item.title 
        let dateLabel = cell.contentView.viewWithTag(2) as! UILabel
        dateLabel.text = item.dateString       

        return cell


    }
    func collectionview(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let horizontalSpace : CGFloat = 20
        let cellSize : CGFloat = self.view.bounds.width / 3 - horizontalSpace
        return CGSize(width: cellSize, height: cellSize)
    }


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    @objc func cellLongPressed(sender: UILongPressGestureRecognizer){

        if sender.state == UIGestureRecognizer.State.began{

           performSegue(withIdentifier: "next", sender: nil)

        }



    }



    var  editingItem: Int?




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


              let nextVC = segue.destination as! NextViewController
               nextVC.delegate = self

           }



}


import UIKit



protocol nextViewControllerDelegate {

    func nextViewController(_ nextVC:NextViewController,didFinishText text: String?)
}


class NextViewController: UIViewController,UITextFieldDelegate {

    //デートピッカー
    var datePicker :UIDatePicker = UIDatePicker()


    @IBOutlet weak var dayTextField: UITextField!


   var delegate: nextViewControllerDelegate?




    override func viewDidLoad() {
        super.viewDidLoad()

    //デートピッカー
        datePicker.datePickerMode = UIDatePicker.Mode.date
        datePicker.timeZone = NSTimeZone.local
        datePicker.locale = Locale(identifier: "ja")
        dayTextField.inputView = datePicker
    //デートピッカーのツールバー関係
        let toolBar = UIToolbar(frame: CGRect(x: 0, y: 0, width: view.frame.size.width, height: 35))
        let spaceItem = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: self, action: #selector(done))
        let doneItem = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(done)); toolBar.setItems([spaceItem,doneItem],animated: true)

        dayTextField.inputView = datePicker
        dayTextField.inputAccessoryView = toolBar

    }
   //デートピッカーを閉じるメソッド
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {

        textField.resignFirstResponder()

        return true
    }
  //デートピッカーにdoneボタン

    @ objc func done(){
        dayTextField.endEditing(true)

        let formatter = DateFormatter()

        formatter.dateFormat = "yyyy年MM月dd日"

        dayTextField.text = "\(formatter.string(from: datePicker.date))"

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()

    }


    @IBAction func addButton(_ sender: Any) {


        delegate?.nextViewController(self, didFinishText: dayTextField.text)

               self.dismiss(animated: true, completion: nil)





    }


}
swift

 import UIKit



struct MyTodoItem {
    var title: String
    var dateString: String? 

}


    class ViewController: UIViewController,UICollectionViewDelegate,UICollectionViewDataSource,UIGestureRecognizerDelegate,nextViewControllerDelegate {





    @IBOutlet weak var babyImage: UIImageView!


    @IBOutlet weak var todoCollection: UICollectionView!

    let toDos = ["1","2","3","4","5","6"]


    var todos: [MyTodoItem] = [
        MyTodoItem(title: "1", dateString: nil),
        MyTodoItem(title: "2", dateString: nil),
        MyTodoItem(title: "3", dateString: nil),
        MyTodoItem(title: "4", dateString: nil),
        MyTodoItem(title: "5", dateString: nil),
        MyTodoItem(title: "6", dateString: nil),
    ]




    override func viewDidLoad() {
        super.viewDidLoad()

        let layout = UICollectionViewFlowLayout()
        layout.sectionInset = UIEdgeInsets(top: 20, left: 20, bottom: 20, right: 20)
        layout.itemSize = CGSize(width: 100,height: 100)
        todoCollection.collectionViewLayout = layout

        let longPressGestureRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(cellLongPressed))
        longPressGestureRecognizer.delegate = self
        longPressGestureRecognizer.allowableMovement = 15
        longPressGestureRecognizer.minimumPressDuration = 0.6
        todoCollection.addGestureRecognizer(longPressGestureRecognizer)

    }

    func nextViewController(_ nextVC: NextViewController, didFinishText text: String?) {

          if let editingItem = self.editingItem {

                    todos[editingItem].dateString = text

                      todoCollection.reloadItems(at: [IndexPath(item: editingItem, section: 0)])
                  }



        }


    //表示するセルの数
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 6
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
        //セルの色
        cell.backgroundColor = .systemPink

        let item = todos[indexPath.row]


        let todoLabel = cell.contentView.viewWithTag(1) as! UILabel
        todoLabel.text = item.title //<-
        let dateLabel = cell.contentView.viewWithTag(2) as! UILabel
        dateLabel.text = item.dateString//<-



        return cell


    }
    func collectionview(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let horizontalSpace : CGFloat = 20
        let cellSize : CGFloat = self.view.bounds.width / 3 - horizontalSpace
        return CGSize(width: cellSize, height: cellSize)
    }


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    @objc func cellLongPressed(sender: UILongPressGestureRecognizer){


        if sender.state == UIGestureRecognizer.State.began{

            performSegue(withIdentifier: "next", sender: nil)




        }




    }



    var  editingItem: Int?




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

    if segue.identifier == "next" {

               let cell = sender as! UICollectionViewCell

               if let indexPath = todoCollection.indexPath(for: cell) {
                   editingItem = indexPath.item
               } else {
                   editingItem = nil
               }


       let nextVC = segue.destination as! NextViewController
                    nextVC.delegate = self

           }



}



}