How to use callback to send back data to previous ViewController - swift

Question

I have 2 ViewControllers like this:
I want when I press button in ViewController will present to ViewController2. Then when I input the text in TextField and press Back Button in ViewController2, will send that text to button in ViewController1.
I can solve this with delegate or using reference the class ViewController in ViewController2. (You can see with my comment code)
But now I want to use CallBack to send back data.
How to do this:
Here is ViewController:
import UIKit
class ViewController: UIViewController {
#IBOutlet var button: UIButton!
var myString = ""
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(animated: Bool) {
button.setTitle(myString, forState: .Normal)
}
#IBAction func goToViewController2(sender: AnyObject) {
let vc2 = storyboard?.instantiateViewControllerWithIdentifier("ViewController2") as! ViewController2
// vc2.vc1 = self
presentViewController(vc2, animated: true, completion: nil)
}
}
And ViewController2:
import UIKit
class ViewController2: UIViewController, UITextFieldDelegate {
#IBOutlet var textField: UITextField!
// var vc1: ViewController?
var callback: ((String) -> Void)?
override func viewDidLoad() {
super.viewDidLoad()
textField.delegate = self
}
func textFieldDidEndEditing(textField: UITextField) {
callback!(textField.text!)
}
#IBAction func backToViewController(sender: AnyObject) {
// vc1?.myString = textField.text!
dismissViewControllerAnimated(true, completion: nil)
}
}
And I don't want to use with completion block in dismiss function, I just want to use my own callback method.

Answer 1

In vc1, set vc2's callback property before presenting it:
#IBAction func goToViewController2(sender: AnyObject) {
let vc2 = storyboard?.instantiateViewControllerWithIdentifier("ViewController2") as! ViewController2
vc2.callback = { <Put your callback code here...> }
presentViewController(vc2, animated: true, completion: nil)
}
And then, in vc2 call the callback function before dismissing the view controller:
#IBAction func backToViewController(sender: AnyObject) {
callback?(textfield.text!)
dismissViewControllerAnimated(true, completion: nil)
}