How to call a first view controller function from second view controller on a button tap in swift ?

Question

I have a requirement where I have to call a first view controller function from second view controller on a button tap.

class FirstViewController: UIViewController {

    @IBAction func firstButtonPressed(_ sender: Any) {
    // Doing ABC
    }

@IBAction func showSecondVC_ sender: Any) {
        // showingSecondVC
        }

}

    class secondViewController: UIViewController {
@IBAction func SecondButtonPressed(_ sender: Any)
    // Dismiss second vc & call First View controller method so that it does ABC.
    }

My first question is can we initiate First VC IBAction directly from second VC ? Is it possible ?

I am thinking to do following

class FirstViewController: UIViewController {

    @IBAction func firstButtonPressed(_ sender: Any) {
    // call DoABC
    }

func DoABC {
// Doing ABC
}

}

    class secondViewController: UIViewController {
@IBAction func SecondButtonPressed(_ sender: Any)
    // Dismiss second vc 
// Call Firstvc.DoABC ?? How to do this ??
    }  

How to call the first vc method from the second vc ??

Answer 1

You have a few options here:

1. Split out the logic, call the same code from each view controller
2. Use a closure callback
3. Use the delegate pattern as a method of calling back

Option 1 - Split out the logic:

class FirstViewController: UIViewController {

  let abcPerformer = ABCPerformer()

  @IBAction func firstButtonPressed(_ sender: Any) {
    abcPerformer.doABC()
  }

  @IBAction func showSecondVC_ sender: Any) {
    // showingSecondVC
  }

}

class SecondViewController: UIViewController {

    let abcPerformer = ABCPerformer()

    @IBAction func SecondButtonPressed(_ sender: Any) { 
      // Dismiss second vc & call First View controller method so that it does ABC.
      abcPerformer.doABC()
    }

}

struct ABCPerformer {

  func doABC() {
    // do ABC
  }

}

Option 2 - Create a callback:

class FirstViewController: UIViewController {

  @IBAction func firstButtonPressed(_ sender: Any) {
    doABC()
  }

  @IBAction func showSecondVC_ sender: Any) {
    // showingSecondVC
    secondVC.doABC = doABC
  }

  func doABC() {
    // do ABC
  }

}

class SecondViewController: UIViewController {

    var doABC: (() -> Void)?

    @IBAction func SecondButtonPressed(_ sender: Any) { 
      // Dismiss second vc & call First View controller method so that it does ABC.
      doABC?()
    }

}

Option 3 - Use a delegate:

protocol ABCProtocol {
  func doABC()
}

class FirstViewController: UIViewController, ABCProtocol {

  @IBAction func firstButtonPressed(_ sender: Any) {
    doABC()
  }

  @IBAction func showSecondVC_ sender: Any) {
    // showingSecondVC
    secondVC.delegate = self
  }

  func doABC() {
    // do ABC
  }

}

class SecondViewController: UIViewController {

    weak var delegate: ABCProtocol?

    @IBAction func SecondButtonPressed(_ sender: Any) { 
      // Dismiss second vc & call First View controller method so that it does ABC.
      delegate?.doABC()
    }

}

There is probably more options too, but these should give you enough choice to make a decision