Swift - How to pass a view controller's refere

问题:

I have a UIViewController and a UIView inside it. When I try to add an alert inside the UIView, I have to use the controller to present the UIAlertController. How do I pass the reference of UIViewController to the UIView class? Or alternatively how do I create a delegate of controller?

class GameViewController: UIViewController {
    @IBOutlet var gameBoardUIView: GameBoardUIView
    ...
}

class GameBoardUIView: UIView {
    ...
    func move() {
        if !gameBoard.checkNextMoveExist() {
            var alert = UIAlertController(title: "Game Over", message: nil, preferredStyle: UIAlertControllerStyle.Alert)
            alert.addAction(UIAlertAction(title: "Ok", style: UIAlertActionStyle.Cancel, handler: {(action: UIAlertAction!) in
                println("Game Over")
            }))
            }))
            // Following would fail because self is not a UIViewController here
            // self.presentViewController(alert, animated: true, completion: nil)
        }
    }
}

回答1:

Following the MVC pattern, a ViewController knows about its Views, but the View shouldn't know about the ViewController. Instead you should declare delegate protocol for GameBoardUIView that your ViewController adopts as follows:

// Delegate protocol declared here
protocol GameBoardUIViewDelegate: class {
    func checkIfNextMoveExistsForGameBoardUIView(gameBoardUIView: GameBoardUIView)
}

class GameBoardUIView: UIView {

    // GameBoardUIView has a delegate property that conforms to the protocol
    // weak to prevent retain cycles
    weak var delegate:GameBoardUIViewDelegate?

    func move() {
        if !gameBoard.checkNextMoveExist() {
            delegate?.checkIfNextMoveExistsForGameBoardUIView(gameBoardUIView: self)
        }
    }

}

// View controller subclass adopts the protocol
class GameViewController: UIViewController, GameBoardUIViewDelegate {

    @IBOutlet var gameBoardUIView: GameBoardUIView!

    override func viewDidLoad() {
        super.viewDidLoad()
        gameBoardUIView.delegate = self
    }

    // Delegte protocol method
    func checkIfNextMoveExistsForGameBoardUIView(gameBoardUIView: GameBoardUIView) {

        let alert = UIAlertController(title: "Game Over", message: nil, preferredStyle: .alert)

        alert.addAction(UIAlertAction(title: "Ok", style: .cancel, handler: {(action: UIAlertAction!) in
            print("Game Over")
        }))

        // If you need to feed back to the game view you can do it in the completion block here
        present(alert, animated: true, completion: nil)
    }
}

回答2:

alternatively, you can also post notifications from your .xib and have the parent viewcontroller observes it. you will be able to send data via userInfo object during the posting.