So let’s assume you have two view controllers: FirstViewController and SecondViewController. The user navigates from FirstViewController to the SecondViewController. SecondViewController will process some business logic and the result of that business logic will need to be sent back to the FirstViewContoller when the user navigates back.

Here I’m using the call back for sending data back from SecondViewController to FirstViewController.

Callback:

-> Callbacks are very important when we are doing any asynchronous task in the background and need to change the UI based on the response.

First Step->

First, we make the call back in SecondViewController.

var callBack: ((_ id: String, _ name: String, _ age: Int)-> Void)?

1	var callBack: ((_ id: String, _ name: String, _ age: Int)-> Void)?

here this callback returns void means nothing.

Second Step->

We will Navigate from FirstViewController to the SecondViewController. here we are using below code to push from FirstViewController to the SecondViewController.

//function for navigate from FirstViewController to SecondViewController

@IBAction func pushToSecond(_ sender: Any) {
        if let vc = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as? SecondViewController {
         
            //callBack block will execute when user back from SecondViewController.
             vc.callBack = { (id: String,name: String,age: Int) in
                print(id,name,age)
            }
            self.navigationController?.pushViewController(vc, animated: true)
        }
    }

//function for navigate from FirstViewController to SecondViewController

@IBAction func pushToSecond(_ sender: Any) {

if let vc = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as? SecondViewController {

//callBack block will execute when user back from SecondViewController.

vc.callBack = { (id: String,name: String,age: Int) in

print(id,name,age)

}

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

}

Third Step->

Now we will call callBack from SecondViewController when the user press on the back button.

//back from SecondViewController to FirstViewController

 @IBAction func BackToFirstWitData(_ sender: Any) {

        //here we call the callBack on back press action
        callBack?("1","Test",22)
        self.navigationController?.popViewController(animated: true)
        
    }

//back from SecondViewController to FirstViewController

@IBAction func BackToFirstWitData(_ sender: Any) {

//here we call the callBack on back press action

callBack?("1","Test",22)

self.navigationController?.popViewController(animated: true)

}

Fourth Step->

In this step, the callback block will execute and print the data.

@IBAction func pushToSecond(_ sender: Any) {
        if let vc = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as? SecondViewController {
         
            //callBack block will execute when user back from SecondViewController.
             vc.callBack = { (id: String,name: String,age: Int) in
            // In this block you can excute anything
                print(id,name,age)
            }
            self.navigationController?.pushViewController(vc, animated: true)
        }
    }

OutPut:- 1,Test,22

@IBAction func pushToSecond(_ sender: Any) {

if let vc = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as? SecondViewController {

//callBack block will execute when user back from SecondViewController.

vc.callBack = { (id: String,name: String,age: Int) in

// In this block you can excute anything

print(id,name,age)

}

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

}

OutPut:- 1,Test,22

Complete Code:-

//FirstViewController

import UIKit

class FirstViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }
    override func viewWillAppear(_ animated: Bool) {
         
    }

    @IBAction func pushToSecond(_ sender: Any) {
        if let vc = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as? SecondViewController {
             vc.callBack = { (id: String,name: String,age: Int) in
                print(id,name,age)
            }
            self.navigationController?.pushViewController(vc, animated: true)
        }
    }
    
}

//FirstViewController

import UIKit

class FirstViewController: UIViewController {

override func viewDidLoad() {

super.viewDidLoad()

// Do any additional setup after loading the view, typically from a nib.

}

override func viewWillAppear(_ animated: Bool) {

}

@IBAction func pushToSecond(_ sender: Any) {

if let vc = storyboard?.instantiateViewController(withIdentifier: "SecondViewController")as? SecondViewController {

vc.callBack = { (id: String,name: String,age: Int) in

print(id,name,age)

}

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

}

//SecondViewController
import UIKit

class SecondViewController: UIViewController {

    var callBack: ((_ id: String, _ name: String, _ age: Int)-> Void)?
    
    @IBAction func BackToFirstWitData(_ sender: Any) {
        
        callBack?("1","Test",22)
        self.navigationController?.popViewController(animated: true)
        
    }
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Do any additional setup after loading the view.
    }
    
}

//SecondViewController

import UIKit

class SecondViewController: UIViewController {

var callBack: ((_ id: String, _ name: String, _ age: Int)-> Void)?

@IBAction func BackToFirstWitData(_ sender: Any) {

callBack?("1","Test",22)

self.navigationController?.popViewController(animated: true)

}

override func viewDidLoad() {

super.viewDidLoad()

// Do any additional setup after loading the view.

}

Conclusion

So pls follow the above step and And if you have any issue or suggestion you can leave your message in the comment section I will try to solve this.

Callback swift callback

jitendra kumar 6 June 2019

. . .

Discuss on Helpdesk

3 comments

Timur Oct 1, 2021 at 3:44 am

YOU ARE GENIUS, THANKS. YOU SAVED 4 HOURS OF DEBUGGING.

jitendra kumar (Moderator) Oct 7, 2021 at 12:07 pm
Your welcome

Reply

Halu Mar 30, 2023 at 2:55 am

I’d like to tell how much you saved my day!! Thank you!!

Pass Data Back To The Previous View Controller Using Callback

Callback:

First Step->

Second Step->

Third Step->

Fourth Step->

Complete Code:-

Conclusion

Leave a Comment Cancel Reply

3 comments

Pass Data Back To The Previous View Controller Using Callback

Callback:

First Step->

Second Step->

Third Step->

Fourth Step->

Complete Code:-

Conclusion

Leave a Comment Cancel Reply

3 comments

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