Pass Data between two View Controller

I call this initializer function from A1

When and where are you calling this function?

I call this function right before I perform the segue with code

Code Block 
// 		function with code for loading the data from core data
print("loaded  " +  caption)
                    self.caption = caption
                    self.size = size as! String
                    self.text = text as! String
                }
            }
            print ("fertig")
        } catch  {
            print(error)
        }
        let vc =  ThirdViewController()
        vc.initializer(caption : caption, size : size, text : text)
//        Segue wird ausgeführt
        performSegue(withIdentifier: "shownext", sender: indexesToRedraw)
    }

I fear you are doing it improperly.

you create

Code Block 
        let vc =  ThirdViewController()

but the segue will instantiate another ThirdViewController.
And you loose everything you have passed to vc which is deleted when exiting the func.

So you should:

• define a prepare for segue func

• include the preparation code in it, but NOT create instance of ThirdViewController

• just call if let vc = segue.destination

Code Block 
     override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
          if segue.identifier == "SegueID" {
               if let destVC = segue.destination as? ThirdViewController {
                    destVC.caption = caption  
                    // Do the same with all properties
                    destVC.fruitCaption = caption
                    destVC.fruitSize = size
               }
          }
     }

Thank you now it works!

(Do not worry, seems I'm too late.)

I call this function right before I perform the segue with code

Thanks for showing the code. (So, ThirdViewController is A2, OK?)

The worst thing in your code is this line:

Code Block 
        let vc =  ThirdViewController()

Instantiating a view controller with init() is almost always a bad idea and would not work as expected.
Especially when the transition is made through a segue, it is iOS to create a new instance, not you.
The instance held in vc of your code is disposed soon after you called initializer(caption:size:text:), and another instance created by iOS will be presented.

---

You need to call initializer(caption:size:text:) for the right instance.
You can get the right instance in prepare(for:sender:).

Code Block 
    ... {
        //...
        
        // Remove the following two lines...
        //let vc =  ThirdViewController()
        //vc.initializer(caption : caption, size : size, text : text)
        //        Segue wird ausgeführt
        performSegue(withIdentifier: "shownext", sender: indexesToRedraw)
    }
    
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "shownext" {
            let vc = segue.destination as! ThirdViewController //<- `segue.destination` is the right instance
            vc.initializer(caption: self.caption, size: self.size, text: self.text)
            //...
        } else {
            //...
        }
    }

---

You need to use the passed values at the right place, but I cannot see if you are doing it correctly or not.