Swift 3: DelegateによるViewController間でのデータ共有

Delegateに変数を宣言

class AppDelegate: UIResponder, UIApplicationDelegate {

var message:String = ""

FirstViewController

変数宣言

let appDelegate = UIApplication.shared.delegate as! AppDelegate

値をセット

appDelegate.message = "message"

SecondViewController

変数を宣言

let appDelegate = UIApplication.shared.delegate as! AppDelegate

値をゲット

let message:String = appDelegate.message