Prepare For Segue on return - swift

Question

So the code I am trying to implement in Swift is based upon this answer here for passing data back from a ViewController:
Passing Data with a Callback
Now my issue is after I have called:
self.navigationController?.popViewController(animated: true)
The Prepare For Segue function isn't called in my original View Controller. I assume it shouldn't be called anyway but from that answer I assume there is a possible way to do so?
First View Controller Snippets
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
//ignore this segue identifier here, this function works when I am showing a new VC
if(segue.identifier == "certSegue"){
let certVC = segue.destination as! CertificateViewController
certVC.profileModel = profileModel
}
//this is what I need to be called
if(segue.identifier == "dpSegue"){
print("dpSegue")
let dpVC = segue.destination as! DatePickerViewController
dpVC.callback = { result in
print(result)
print("Data")
// do something with the result
}
//dpVC.dailyBudgetPassedThrough = "Test"
}
}
func showDatePicker(){
let vc = UIStoryboard.init(name: "Main", bundle: Bundle.main).instantiateViewController(withIdentifier: "DatePickerVC") as? DatePickerViewController
self.navigationController?.pushViewController(vc!, animated: true)
}
Second View Controller
import UIKit
class DatePickerViewController: UIViewController {
var callback : ((String)->())?
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
func sendBackUpdate(){
print("Callback")
callback?("Test")
}
#IBAction func cancelButton(_ sender: Any) {
self.navigationController?.popViewController(animated: true)
}
#IBAction func updateButton(_ sender: Any) {
sendBackUpdate()
self.navigationController?.popViewController(animated: true)
}
}

Answer 1

prepareForSegue is called if in Interface Builder a segue is connected
from a table/collection view cell to a destination view controller and the cell is tapped.
from a source view controller to a destination view controller and performSegue(withIdentifier:sender:) is called in the source view controller.
It's not called when a view controller is going to be presented with pushViewController
In your case assign the callback after instantiating the controller in showDatePicker, prepare(for segue is not needed.
func showDatePicker(){
let vc = UIStoryboard(name: "Main", bundle: .main).instantiateViewController(withIdentifier: "DatePickerVC") as! DatePickerViewController
vc.callback = { result in
print(result)
print("Data")
// do something with the result
}
self.navigationController?.pushViewController(vc, animated: true)
}