将数据从一个UIViewController委派给另一个UIViewController

Question

I am completely new to Swift programming and tried to delegate a single String from one ViewController to another by clicking a send button . The problem is , that it does not work ...

I guess it would be easy for you to solve this and considering that it would be very helpful wether you explain me what I did wrong. :)

Thank you a lot

import UIKit


protocol protoTYdelegate {
    func didSendMessage(message: String)
}


class New: UIViewController {

    @IBOutlet weak var SendButton: UIButton!

    var tydelegate: protoTYdelegate?

    override func viewDidLoad() {
        super.viewDidLoad()

    }





    @IBAction func SendButtonAction(_ sender: Any) {

        let nachricht = "It works fine."
        tydelegate?.didSendMessage(message: nachricht)

    }

}

import UIKit


class ThankYouPage: UIViewController {


    @IBOutlet weak var numbersView: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        let controller = New()
        controller.tydelegate = self

    }

}

extension ThankYouPage: protoTYdelegate{
    func didSendMessage(message: String) {
        numbersView.text = message
    }

Answer 1

As far as I understand, this code block doesn't work but the problem is not in the code, it's actually way that you choose to send data. In iOS development, there are many ways to send data. In your case, you need to use prepareForSegue method to send data to new class, not necessary to use delegates.

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if (segue.identifier == "ThankYouPage") {
    let vc = segue.destination as! ThankYouPage
    vc.message = "Message that you want to send"
    }
}

And you need to implement your ThankYouPage as:

class ThankYouPage: UIViewController {

@IBOutlet weak var numbersView: UILabel!
var message = ""

override func viewDidLoad() {
    super.viewDidLoad()

    numbersView.text = message
}

}

In addition to that, you can use didSet method to print out the message to label instead of printing it directly in viewDidLoad method. Simply:

class ThankYouPage: UIViewController {

@IBOutlet weak var numbersView: UILabel!
var message: String?{
    didSet{
      numbersView.text = message
  }
} 

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

}

I hope this helps you.

Answer 2

@Eyup Göymen 's answer is right.

I have another way, assuming that you are not using segue and you are pushing to next controller by manual-code.

So your ThankYouPage code should be like :

import UIKit

class ThankYouPage: UIViewController {

    @IBOutlet weak var numbersView: UILabel!

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

    @IBAction func someButtonAction(_ sender: Any) { // By clicking on some, you are opening that `New` controller
         let detailView = self.storyboard?.instantiateViewController(withIdentifier: "New") as! New
         detailView.tydelegate = self
         self.navigationController?.pushViewController(detailView, animated: true)
    }
}

extension ThankYouPage: protoTYdelegate {

     func didSendMessage(message: String) {
         numbersView.text = message
    }
}