How to use Protocol Delegate in iOS using Swift language

Define Protocol

There are two controllers:
FirstViewController
SecondViewController

I need to notify FirstViewController that SecondViewController ViewDidAppearCalled

import UIKit

//Define Your protocole here after Import

protocol SecondViewControllerDelegate{

      

    //Add a new function

    func SecondViewDidLoadFinished(controller:SecondViewController)

}

class SecondViewController: UIViewController {

   

    

    var delegate:SecondViewControllerDelegate?

    override func viewDidLoad() {

        super.viewDidLoad()

    }

override func viewDidAppear(animated: Bool) {

        

        if let delegate = self.delegate{

            delegate.SecondViewDidLoadFinished(self)

        }

    }

First view

import UIKit

class FirstViewController: UIViewController,SecondViewControllerDelegate {

    

    override func viewDidLoad() {

        super.viewDidLoad()

    }

@IBAction func buttonTapped(sender:UIButton){

        

        let mapObject:SecondViewController = SecondViewController()

        mapObject.delegate = self

        self.navigationController?.pushViewController(mapObject, animated: true)   

    }

func SecondViewDidLoadFinished(controller: SecondViewController) {

//Here you will be notified that second view viewDid appear loaded

        

    }