为什么我的Swift Playground中没有任何显示？

Question

I have a pong game in a Swift Playground that I made by following a tutorial online but my assistant editor won't show anything! Where is my pong game!? My code is below the image, which shows that nothing is showing up.

import SpriteKit
import PlaygroundSupport

// Declare some global constants
let width = 800 as CGFloat
let height = 1200 as CGFloat
let racketHeight = 150 as CGFloat
let ballRadius = 20 as CGFloat

// Three types of collision objects possible
enum CollisionTypes: UInt32 {
    case Ball = 1
    case Wall = 2
    case Racket = 4
}

// Racket direction
enum Direction: Int {
    case None = 0
    case Up = 1
    case Down = 2
}

// Make a SpriteKit scene
class gameScene: SKScene, SKPhysicsContactDelegate {
    let racketSpeed = 500.0
    var direction = Direction.None
    var score = 0
    var gameRunning = false

    // Screen elements
    var racket: SKShapeNode?
    var ball: SKShapeNode?
    let scoreLabel = SKLabelNode()

    // Initialize objects during first start
    override func sceneDidLoad() {
        super.sceneDidLoad()
        scoreLabel.fontSize = 40
        scoreLabel.position = CGPoint(x: width/2, y: height - 100)
        self.addChild(scoreLabel)

        createWalls()
        createBall(position: CGPoint(x: width / 2, y: height / 2))
        createRacket()
        startNewGame()
        self.physicsWorld.contactDelegate = self
    }

    // Create the ball sprite
    func createBall(position: CGPoint) {
        let physicsBody = SKPhysicsBody(circleOfRadius: ballRadius)
        ball = SKShapeNode(circleOfRadius: ballRadius)
        physicsBody.categoryBitMask = CollisionTypes.Ball.rawValue
        physicsBody.collisionBitMask = CollisionTypes.Wall.rawValue | CollisionTypes.Ball.rawValue | CollisionTypes.Racket.rawValue
        physicsBody.affectedByGravity = false
        physicsBody.restitution = 1
        physicsBody.linearDamping = 0
        physicsBody.velocity = CGVector(dx: -500, dy: 500)
        ball!.physicsBody = physicsBody
        ball!.position = position
        ball!.fillColor = SKColor.white
    }

    // Create the walls
    func createWalls() {
        createWall(rect: CGRect(origin: CGPoint(x: 0, y: 0), size: CGSize(width: ballRadius, height: height)))
        createWall(rect: CGRect(origin: CGPoint(x: 0, y: 0), size: CGSize(width: width, height: ballRadius)))
        createWall(rect: CGRect(origin: CGPoint(x: 0, y: height - ballRadius), size: CGSize(width: width, height: ballRadius)))
    }

    func createWall(rect: CGRect) {
        let node = SKShapeNode(rect: rect)
        node.fillColor = SKColor.white
        node.physicsBody = getWallPhysicsbody(rect: rect)
        self.addChild(node)
    }

    // Create the physics objetcs to handle wall collisions
    func getWallPhysicsbody(rect: CGRect) -> SKPhysicsBody {
        let physicsBody = SKPhysicsBody(rectangleOf: rect.size, center: CGPoint(x: rect.midX, y: rect.midY))
        physicsBody.affectedByGravity = false
        physicsBody.isDynamic = false
        physicsBody.collisionBitMask = CollisionTypes.Ball.rawValue
        physicsBody.categoryBitMask = CollisionTypes.Wall.rawValue
        return physicsBody
    }

    // Create the racket sprite
    func createRacket() {
        racket =  SKShapeNode(rect: CGRect(origin: CGPoint.zero, size: CGSize(width: ballRadius, height: racketHeight)))
        self.addChild(racket!)
        racket!.fillColor = SKColor.white
        let physicsBody = SKPhysicsBody(rectangleOf: racket!.frame.size, center: CGPoint(x: racket!.frame.midX, y: racket!.frame.midY))
        physicsBody.affectedByGravity = false
        physicsBody.isDynamic = false
        physicsBody.collisionBitMask = CollisionTypes.Ball.rawValue
        physicsBody.categoryBitMask = CollisionTypes.Racket.rawValue
        physicsBody.contactTestBitMask = CollisionTypes.Ball.rawValue
        racket!.physicsBody = physicsBody
    }

    // Start a new game
    func startNewGame() {
        score = 0
        scoreLabel.text = "0"
        racket!.position = CGPoint(x: width - ballRadius * 2, y: height / 2)
        let startLabel = SKLabelNode(text: "Game Over")
        startLabel.position = CGPoint(x: width / 2, y: height / 2)
        startLabel.fontSize = 160
        self.addChild(startLabel)

        // Animated countdown
        let fadeIn = SKAction.fadeIn(withDuration: 0.5)
        let fadeOut = SKAction.fadeOut(withDuration: 0.5)
        startLabel.text = "3"
        startLabel.run(SKAction.sequence([fadeIn, fadeOut]), completion: {
            startLabel.text = "2"
            startLabel.run(SKAction.sequence([fadeIn, fadeOut]), completion: {
                startLabel.text = "1"
                startLabel.run(SKAction.sequence([fadeIn, fadeOut]), completion: {
                    startLabel.text = "0"
                    startLabel.run(SKAction.sequence([fadeIn, fadeOut]), completion: {
                        startLabel.removeFromParent()
                        self.gameRunning = true
                        self.ball!.position = CGPoint(x: 30, y: height / 2)
                        self.addChild(self.ball!)
                    })
                })
            })
        })
    }

    // Handle touch events to move the racket
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        for touch in touches {
            let location = touch.location(in: self)
            if location.y > height / 2 {
                direction = Direction.Up
            } else if location.y < height / 2{
                direction = Direction.Down
            }
        }
    }

    // Stop racket movement
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        direction = Direction.None
    }

    // Game loop:
    var dt = TimeInterval(0)
    override func update(_ currentTime: TimeInterval) {
        if gameRunning {
            super.update(currentTime)
            checkGameOver()
            if dt > 0 {
                moveRacket(dt: currentTime - dt)
            }
            dt = currentTime
        }
    }

    // Move the racket up or down
    func moveRacket(dt: TimeInterval) {
        if direction == Direction.Up && racket!.position.y < height - racketHeight {
            racket!.position.y = racket!.position.y + CGFloat(racketSpeed * dt)
        } else if direction == Direction.Down && racket!.position.y > 0 {
            racket!.position.y = racket!.position.y - CGFloat(racketSpeed * dt)
        }
    }

    // Check if the ball is still on screen
    // Game Over animation
    func checkGameOver() {
        if ball!.position.x > CGFloat(width) {
            gameRunning = false
            ball!.removeFromParent()
            let gameOverLabel = SKLabelNode(text: "Game Over")
            gameOverLabel.position = CGPoint(x: width / 2, y: height / 2)
            gameOverLabel.fontSize = 80
            self.addChild(gameOverLabel)

            // Game Over animation
            let rotateAction = SKAction.rotate(byAngle: CGFloat(M_PI), duration: 1)
            let fadeInAction = SKAction.fadeIn(withDuration: 2)
            gameOverLabel.run(SKAction.repeat(rotateAction, count: 2))
            gameOverLabel.run(SKAction.scale(to: 0, duration: 2.5), completion: {
                gameOverLabel.removeFromParent()
                self.startNewGame()
            })
        }
    }

    // Detect collisions between ball and racket to increase the score
    func didBegin(_ contact: SKPhysicsContact) {
        if contact.bodyA.categoryBitMask == CollisionTypes.Racket.rawValue || contact.bodyB.categoryBitMask == CollisionTypes.Racket.rawValue {
            score += 1
            scoreLabel.text = String(score)
        }
    }
}

//Initialize the playground and start the scene:
let skView = SKView(frame: CGRect(origin: CGPoint.zero, size: CGSize(width: width, height: height)))
let scene = gameScene(size: skView.frame.size)
skView.presentScene(scene)

PlaygroundPage.current.liveView = skView

Answer 1

This happens to me sometimes. Playgrounds with SpriteKit just would not show anything in the Timeline view - you do have the Timeline view open, right? If you don't, tap the "Show the Assistant editor" button on the toolbar to open the Timeline view.

If you have the Timeline view open and nothing shows, try shutting down Xcode and restarting it. That generally resolves this issue for me.