ios - 调用协议(protocol)方法时出现 "fatal error: unexpectedly found nil while unwrapping an Optional value"

Question

我已经实现了一个协议(protocol)来获取某种消息，游戏已经完成并将时间传递给我的 Controller (在 SpriteKit 中编写的游戏)。但是现在我在完成游戏并执行 gameEnded 方法后遇到了这个 fatal error ，应用程序崩溃了。有谁知道为什么？

这是我的代码

游戏 View Controller

class AcceleratorGameController: UIViewController {

var time: Float = 0.0
var challengeController: ChallengeViewController!
weak var delegate : GameEnded?

override func viewDidLoad() {
    super.viewDidLoad()
    if let scene = AcceleratorGame.unarchiveFromFile("AcceleratorGame") as? AcceleratorGame {

        let skView = self.view as! SKView
        skView.showsFPS = true
        scene.viewController = self

        skView.ignoresSiblingOrder = true

        scene.scaleMode = .AspectFill
        skView.presentScene(scene)
    }
}


override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    var dest : ChallengeViewController = segue.destinationViewController as! ChallengeViewController
    dest.gameHasFinished(time) //Dont know if this does anything...
    println("Segue now!")
}

override func viewWillDisappear(animated: Bool) {
    super.viewWillDisappear(true)
    println("View will disapear")

    delegate.gameHasFinished(self.time) // ###CRASHES HERE!###
}

这是我的另一个 ViewController

protocol GameEnded : class {
     func gameHasFinished(time: Float)
}

class ChallengeViewController : UIViewController, GameEnded {

var time : Float = 0.0
var acceleratorGameController : AcceleratorGameController!

override func viewDidLoad() {
    super.viewDidLoad()
    println("ChallengeViewController geladen")
    startGame()
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "accelGame" {
        acceleratorGameController = segue.destinationViewController as! AcceleratorGameController
        acceleratorGameController.delegate = self
    }
}
func startGame () {
    println("Start Game")

    self.showAccelGameView()
}
func gameHasFinished(time: Float) {
    println("Game has finished")
    self.time = time
}
func showAccelGameView() {

    println("Show Accel Game")
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let vc = storyboard.instantiateViewControllerWithIdentifier("AcceleratorGameController") as! AcceleratorGameController

    self.navigationController?.pushViewController(vc, animated: true)
}

编辑:我做了你告诉我的所有事情，但它仍然在同一点崩溃。 Xcode 告诉我使用委托(delegate)。我什么时候做委托(delegate)？它有效，但这不是我想要的。必须调用该函数!

func gameOver(time: Float) {
    println("Game Over")
    self.time = time
    //delegate!.gameHasFinished(time) still crashes here. added !. i commented it to test the prepareForSegue method
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    var dest : ChallengeViewController = segue.destinationViewController as! ChallengeViewController
    dest.gameHasFinished(time)
    println("Segue now!") // Wont happen
    self.navigationController?.popViewControllerAnimated(true) //Wont happen either. If i call this in gameOver() it works.
}

我在 prepareForSegue() 方法中加入了一些 println()，但不知何故它们不会被执行。我必须以某种方式给他们打电话吗？这是我的 segue 的屏幕截图。

http://i.stack.imgur.com/oK4Ce.png

我也试过以相反的方式加入一个 segue，但这也无济于事。

http://i.stack.imgur.com/TVmdP.png (没有标识符，因为它是唯一的 segue。)

我忘了说这个 AcceleratorGameController 背后的 SpriteKit Game 在完成时会调用 gameOver() 方法。

Answer 1

首先，一些提示:

• 始终尝试以下列方式声明您的协议(protocol)(当引用委托(delegate) 模式时):

  protocol GameEnded : class {
      func gameHasFinished(time: Float)
  }
  

  通过上述方式，您可以声明您的delegate 变量weak 并避免强引用。

• 你的类 weak var 应该是这样的:

  class AcceleratorGameController: UIViewController {
  
     weak var delegate : GameEnded?
  
     // rest of your code
  }
  

最后，您应该保留一个引用作为类 AcceleratorGameController 的全局变量，以在 prepareForSegue 中设置为您的delegate，像下面这样:

class ChallengeViewController : UIViewController, GameEnded {

    var acceleratorGameController : AcceleratorGameController! 

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
         if segue.identifier == "accelGane" {
             acceleratorGameController = segue.destinationViewController as! AcceleratorGameController
             acceleratorGameController.delegate = self
         }
    }
}

上面的代码应该可以解决您的问题。希望对您有所帮助。