I'm unable to pass data from one VC to another [duplicate] - ios

Question

This question already has answers here:
Passing data with unwind segue
(3 answers)
Closed 5 years ago.
I'm passing the data from one VC back to the first VC. I'm using this code:
#IBAction func goBack(_ sender: Any) {
dismiss(animated: true, completion: nil)
print(self.entryField.text!)
performSegue(withIdentifier: "sendText", sender: self)
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let destVC = segue.destination as! ViewController
let printName = self.entryField.text!
print(self.entryField.text!)
destVC.nameToDisplay=printName
}
This is my code of the VC in which the data is.
The code of the VC in which I want to display my result.
var nameToDisplay = ""
override func viewWillAppear(_ animated: Bool) {
titleDisplay.text=nameToDisplay
}
I'm unable to pass the data, I tried printing the nameToDisplay but it gives empty string.

Answer 1

A reasonable pattern for passing back the value from second controller to the first one could be like this:
class FirstViewController: UIViewController {
//......
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let secondViewController = segue.destination as? SecondViewController {
secondViewController.nameHandler = { (name) -> Void in
titleDisplay.text=nameToDisplay //second controller will call back here to pass the name value when it's going back.
}
}
}
//......
}
class SecondViewController: UIViewController {
//......
var nameHandler:((_ name:String)->Void)? //a closure to call back name
#IBAction func goBack(_ sender: Any) {
if let name = self.entryField.text {
self.nameHandler?(name) //call back and pass the name to the first controller
}
dismiss(animated: true, completion: nil)
}
//......
}

Answer 2

You are looking for one to one communication between viewcontrollers. This can be achieved by different ways in iOS.
1- Delegation
2- blocks, closures.
The above solution is using block. I will tell you with delegates
class FirstVC: UIViewController, PassData {
func pushVC() {
let secondVC = SecondVC()
secondVC.delegate = self
self.navigationController?.pushViewController(secondVC, animated: true)
}
func passDataOnDismiss(data: String) {
print(data)
}}
protocol PassData: class {
func passDataOnDismiss(data: String)
}
class SecondVC: UIViewController {
weak var delegate: PassData?
#IBAction func didButtonPress() {
self.delegate?.passDataOnDismiss(data: "I am passing this string back to First VC")
self.navigationController?.popViewController(animated: true)
}
}