Unable to pass information to the previous ViewController

Question

I know that there are few questions and answers regarding this topic, but believe me when I say that I have checked them before posting this questions.

I am trying to pass information to a controller (which was the previous one shown). As a summary, I am trying to send information from the second controller, SearchViewController, to Tthe first controller MainViewController (which is embedded in a navigation controller).

I have tried several ways to do it, but no one is exactly what I am looking for. I will paste each of them, and the explanation of the problem:

Note

Please note that I am avoiding using segue, so it is not an option.

Attempt 1

The navigation is correctly made. It is shown as full screen, and not a popping window, what is correct. Nevertheless, it does not keep the changes done for coordinate and it takes the default value, what makes me believe that it is a new instance and not the one I am trying to navigate to.

@IBAction func setCoordinate(_ sender: UIBarButtonItem) {
      // Set the new values of from/to coordinates and navigates to the main controller
    if((self.coordinate) {
          // Full screen. Navigation controller shown. Does not keep the changes in variables
          let vc = MainViewController()
          vc.setCoordinate(coordinate: self.coordinate!)
          navigationController?.popToRootViewController(animated: true)

      } else {
          showToast(message: "Please, enter the coordinate")
      }
  }

Attempt 2 The navigation is correctly made and keeps the changes made on coordinate.Nevertheless, it is shown as a popping window and the navigation controller is not shown anymore.

@IBAction func setCoordinate(_ sender: UIBarButtonItem) {
      // Set the new values of from/to coordinates and navigates to the main controller
    if((self.coordinate) {
          // Pop window. Not full screen. Navigation controller not shown. Keeps the variable values
         let storyBoard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
         let mainViewController = storyBoard.instantiateViewController(withIdentifier: "mainViewControllerID") as! MainViewController
         mainViewController.setCoordinate(fcoordinate: coordinate!)
         self.present(mainViewController, animated: true, completion: nil)

      } else {
          showToast(message: "Please, enter the coordinate")
      }
  }

Attempt 3

I used this approach because I am trying to come back to the previous controller, but dismiss is not navigating anywhere, so it is failing.

@IBAction func setCoordinate(_ sender: UIBarButtonItem) {
      // Set the new values of from/to coordinates and navigates to the main controller
    if((self.coordinate) {
         // Does not come back to the previous controller
         let storyBoard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
         let mainViewController = storyBoard.instantiateViewController(withIdentifier: "mainViewControllerID") as! MainViewController
         mainViewController.setCoordinate(coordinate: coordinate!)
         self.dismiss(animated: true, completion: nil)

      } else {
          showToast(message: "Please, enter the coordinate")
      }
  }

Attempt 4

This approach does not allow me to access the methods/variables of mainViewController so I can not change the value of coordinate. Furthermore, the ViewController is showing as a popping window and not in full screen

@IBAction func setCoordinate(_ sender: UIBarButtonItem) {
      // Set the new values of from/to coordinates and navigates to the main controller
    if((self.coordinate) {
         // Pop window. Not full screen. No access to methods
         guard let vc = self.storyboard?.instantiateViewController(withIdentifier: "mainViewControllerID") else { return }
         let navController = UINavigationController(rootViewController: vc)
         self.navigationController?.present(navController, animated: true, completion: nil)

      } else {
          showToast(message: "Please, enter the coordinate")
      }
  }

Attempt 5

Navigation is correct. It is in full screen, what is good, but navigation controller is not shown. It does not keep the changes made in coordinate

@IBAction func setCoordinate(_ sender: UIBarButtonItem) {
          // Set the new values of from/to coordinates and navigates to the main controller
        if((self.coordinate) {
            // Full screen. Navigation controller shown. Does not keep the changes in variables
            let vc = MainViewController()
            vc.setCoordinate(coordinate: self.coordinate!)
            self.navigationController?.popViewController(animated: true)

          } else {
              showToast(message: "Please, enter the coordinate")
          }
      }

Answer 1

All your attempts instantiate a new vc other then the real presented previous one marked with let vc = MainViewController() or storyBoard.instantiateViewController so you need

let arr = self.navigationController!.viewControllers
let prev = arr[arr.count - 2] as! MainViewController
prev.setCoordinate(coordinate: self.coordinate!)
self.navigationController!.popToRootViewController(animated: true)