Protocol Delegate Method is not called in Swift

Question

Protocol delegate method is not called..

First View controller code

class ViewController: UIViewController,customDelegate {

  var seconviewcontroller : SecondViewController = SecondViewController()
  @IBOutlet weak var Label: UILabel!
    override func viewDidLoad() {
        super.viewDidLoad()

    seconviewcontroller.delegate = self
}
func didSelectData(_ result: String) {

    Label.text = result
  print("Didselect Data Call")

}

Second view controller code

import UIKit
protocol customDelegate: class {
    func didSelectData(_ result: String)
}

class SecondViewController: UIViewController {
     var delegate: customDelegate?

@IBOutlet weak var secondbutton: UIButton!

override func viewDidLoad() {
    super.viewDidLoad()
}

@IBAction func secondbuttonclick(_ sender: Any) {
     let selectedItem = "naga"

     delegate?.didSelectData(selectedItem)
}

how to call the func didSelectData pls help me

Lawliet · Accepted Answer · 2017-08-04 09:09:30Z

4

As you've already used segue for navigating between views. You can also use that for this example. I give the following as a code sample so that you can track back yourself to detect issue in your code.

First View Controller

import UIKit

class ViewController: UIViewController, SecondVCDelegate {
    @IBOutlet weak var label: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let secondVC = segue.destination as? SecondViewController {
            secondVC.delegate = self
        }
    }        

    func didSelectData(_ result: String) {
        label.text = result
        print(result)
    }
}

Second View Controller

import UIKit

protocol SecondVCDelegate: class {
    func didSelectData(_ result: String)
}

class SecondViewController: UIViewController {
    @IBOutlet weak var button: UIButton!

    weak var delegate: SecondVCDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func buttonTapped(_ sender: UIButton) {
        delegate?.didSelectData("My result")
        dismiss(animated: true, completion: nil)
    }
}

edited Aug 4, 2017 at 9:09

answered Jul 20, 2017 at 12:38

Lawliet

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5 Comments

Lawliet Over a year ago

No worries, glad it helps.

naga Over a year ago

I have to pass the data with first view controller to second view controller I know segue is there but I have to use protocol delegate pls help how to do

naga Over a year ago

I had count of the students in First view controller I have to pass that data count to second view controller how to pass that with out segue/ user defaults I want print that count at second view controller

naga Over a year ago

if I can take the instance as Global i will access the count of the student in another controller

Lawliet Over a year ago

There are various ways of passing data from 1 view controller to the other. If you don't you segue anymore, but use navigation, from the first VC you can simply do seconVC.dataList = self.dataList and navigationController?.pushViewController(secondVC, animated: true).

Salman Ghumsani · Accepted Answer · 2017-07-20 12:10:10Z

2

So basically in line var seconviewcontroller : SecondViewController = SecondViewController() is different from your pushing view controller instance.

You are making a separate instance of SecondViewController so you have done delegate self at the time of pushing with pushes object like that

let secondVCInstance = self.storyboard?.instantiateViewController(withIdentifier: "SecondViewController") as! SecondViewController
secondVCInstance.delegate = self
self.navigationController?.pushViewController(secondVCInstance, animated: true)

NOTE: - EVERY OBJECT HAS ITS OWN PROPERTIES

answered Jul 20, 2017 at 12:10

Salman Ghumsani

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Comments

Frankich · Accepted Answer · 2020-10-21 13:11:31Z

First View Controller

import UIKit

class ViewController: UIViewController, SecondVCDelegate {
    @IBOutlet weak var label: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if let secondVC = segue.destination as? SecondViewController {
            secondVC.delegate = self
        }
    }        

    func didSelectData(_ result: String) {
        label.text = result
        print(result)
    }
}

Second View Controller

import UIKit

protocol SecondVCDelegate: class {
    func didSelectData(_ result: String)
}

class SecondViewController: UIViewController {
    @IBOutlet weak var button: UIButton!

    weak var delegate: SecondVCDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    @IBAction func buttonTapped(_ sender: UIButton) {
        delegate?.didSelectData("My result")
        dismiss(animated: true, completion: nil)
    }
}

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