Data transfer between view controllers

1.Use segue between button and thirdVC

• check button is connected to thirdVC
• this method is called automatically when we use segue to connect two view controllers

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        var result:String = ""
        guard let num = Int(numberTextField.text!) else {
            return
        }

        if num % 2 == 0 {
            result = "Even"
        } else {
            result = "Odd"
        }

        guard let vc = segue.destination as? thirdVC else {
            return
        }
        vc.result = result
    }

2.Use segue between whole secondVC and thirdVC

• click square on secondVC - connect to thirdVC
• click segue and give identifier in the insepector area (navigateToThirdVC) under storyboard segue > identifier
• this line will initiate relationship between secondVC and thirdVC

performSegue(withIdentifier: "navigateToThirdVC", sender: nil)

3.Give unique identifier to thirdVC

• click thirdVC controller > identity inspector > Storyboard ID > resultVC
• get a reference to the result screen (thirdVC)
• this does not use segue at all! -> so don't need prepare() method

guard let resultScreen = storyboard?.instantiateViewController(withIdentifier: "resultVC") as? thirdVC else {
            print("can't find thirdVC")
            return
}

// pass the data to thirdVC
resultScreen.result = result

// Several options we can get to the thirdVC

// 1.navigate to result screen using parent contoller - navigationController
// this way, this page have back button!
self.navigationController?.pushViewController(resultScreen, animated: true)

// 2.we can also use modal presentation instead of navigationController
// this will pop up like a card! user can dismiss the card!
self.present(resultScreen, animated: true)

// 3.another option in modal presentation - card that user can't dismiss! (force)
resultScreen.modalPresentationStyle = .fullScreen
self.present(resultScreen, animated: true)