Pass data back from a popped ViewController using Swift

Question

I would like to know how do we pass a data back from a popped ViewController

FirstViewController -----push----> SecondViewController

SecondViewController -----popped(Pass Value?) ----> FirstViewController

I have searched around and found many solutions asking to use delegates, but those are in Objective C which I am not familiar with.

How do we do this in Swift?

Thank you

@AstroCB http://stackoverflow.com/questions/6203799/dismissmodalviewcontroller-and-pass-data-back — JayVDiyk, Feb 06 '15 at 03:20
@AstroCB http://stackoverflow.com/questions/14468995/passing-data-back-with-multiple-viewcontrollers-using-delegates — JayVDiyk, Feb 06 '15 at 03:21

TheCodingArt · Accepted Answer · 2015-02-06T03:32:41.050

Actually delegates are not just available in Objective C. Delegation is available in Swift (anything that does not involve the dynamic nature of Objective-C is able in Swift) and delegation is a design pattern (delegation as a design pattern), not a language implementation. You can use one of two methodologies, blocks/closures, or delegation. An example of delegation in swift can be found in Apple's documentation as referenced here:

Apple documentation on delegation

You may also see references for Apple's documentation on closures here: Apple documentation on closures

An example of delegation can be shown below:

Noted that the delegate is declared via the protocol below:

protocol DiceGame {
    var dice: Dice { get }
    func play()
}
protocol DiceGameDelegate {
    func gameDidStart(game: DiceGame)
    func game(game: DiceGame, didStartNewTurnWithDiceRoll diceRoll: Int)
    func gameDidEnd(game: DiceGame)
}

The class checks if it has a delegate, if it does, it calls the methods the class must implement by conforming to the protocol above

  class SnakesAndLadders: DiceGame {
        let finalSquare = 25
        let dice = Dice(sides: 6, generator: LinearCongruentialGenerator())
        var square = 0
        var board: [Int]
        init() {
            board = [Int](count: finalSquare + 1, repeatedValue: 0)
            board[03] = +08; board[06] = +11; board[09] = +09; board[10] = +02
            board[14] = -10; board[19] = -11; board[22] = -02; board[24] = -08
        }
        var delegate: DiceGameDelegate?
        func play() {
            square = 0
            delegate?.gameDidStart(self)//Calls the method gameDidEnd on the delegate passing self as a parameter
            gameLoop: while square != finalSquare {
                let diceRoll = dice.roll()
                delegate?.game(self, didStartNewTurnWithDiceRoll: diceRoll)
                switch square + diceRoll {
                case finalSquare:
                    break gameLoop
                case let newSquare where newSquare > finalSquare:
                    continue gameLoop
                default:
                    square += diceRoll
                    square += board[square]
                }
            }
            delegate?.gameDidEnd(self)//Calls the method gameDidEnd on the delegate passing self as a parameter
        }
    }

As a side note on this answer, I would highly advice you to learn Objective-C before Swift. The reason I state this is I've recently seen a trend of people learning Swift first and not understanding that the APIs and design patterns between Swift and Obj-C are not different. You should be able to read both and understand both. People going down the Swift root appear to be ignorant to this (and professionally this is going to do more harm than good). Currently, you must understand at least how to read Obj-C to program for iOS... period. — TheCodingArt, Feb 06 '15 at 03:30

Pass data back from a popped ViewController using Swift

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