Pong-after a restart no ball on screen - swift

Question

I'm a newbee in Swift and SpriteKit. I have made a simple one player version of Pong. After a score the game restarts. Switches to the Game Over scene and returns. After that I cannot get the ball back on the screen. I do not understand that the spawnBall() does not reply, while the spawnPaddle, and the spawnBottom() do. Please help.
import SpriteKit
class GameScene: SKScene, SKPhysicsContactDelegate {
required init?(coder aDecoder: NSCoder) { super.init(coder: aDecoder) }
override init(size: CGSize) { super.init(size: CGSize()) }
var gameScene: GameScene!
let BallCategoryName = "ball" let BottomCategoryName = "bottom" let PaddleCategoryName = "paddle"
var isFingerOnPaddle = false
let BallCategory: UInt32 = 0x1 << 0
let BottomCategory : UInt32 = 0x1 << 1
let PaddleCategory : UInt32 = 0x1 << 3
var score = 0
var start: UIButton!
var isRunning = false
var scoreLabel = SKLabelNode()
var ball = SKSpriteNode()
var paddle = SKSpriteNode()
var bottom = SKSpriteNode()
var isBall = false
func spawnBall() {
ball = SKSpriteNode(imageNamed: "ball")
ball.position = CGPoint(x: CGRectGetMidX(frame), y: CGRectGetMidY(frame))
ball.xScale = 0.1
ball.yScale = 0.1
ball.hidden = false
ball.physicsBody = SKPhysicsBody(circleOfRadius: ball.size.height/2)
ball.physicsBody?.categoryBitMask = BallCategory
ball.physicsBody?.contactTestBitMask = BottomCategory
ball.physicsBody?.restitution = 1.0
ball.physicsBody?.linearDamping = 0.0
ball.physicsBody?.angularDamping = 0.0
addChild(ball)
isBall = true
println("***")
}
func spawnPaddle() {
paddle = SKSpriteNode(imageNamed: "wit")
paddle.position = CGPointMake(200, 50)
paddle.xScale = 0.09
paddle.yScale = 0.09
paddle.physicsBody = SKPhysicsBody(rectangleOfSize: paddle.size)
paddle.physicsBody?.categoryBitMask = PaddleCategory
paddle.physicsBody?.contactTestBitMask = BottomCategory
paddle.physicsBody?.restitution = 1.0
paddle.physicsBody?.linearDamping = 0.0
paddle.physicsBody?.angularDamping = 0.0
paddle.physicsBody?.dynamic = false
paddle.name = "paddle"
addChild(paddle)
}
func spawnBottom() {
bottom = SKSpriteNode(imageNamed: "wit")
bottom.position = CGPointMake(0, -111)
bottom.physicsBody = SKPhysicsBody(rectangleOfSize: bottom.size)
bottom.physicsBody?.dynamic = false
bottom.physicsBody?.restitution = 1
bottom.physicsBody?.angularDamping = 0
bottom.physicsBody?.linearDamping = 0.0
bottom.physicsBody?.categoryBitMask = BottomCategory
addChild(bottom)
println("Bottom")
}
override func didMoveToView(view: SKView) {
super.didMoveToView(view)
physicsWorld.gravity = CGVectorMake(0, 0)
physicsWorld.contactDelegate = self
backgroundColor = UIColor.blackColor()
scoreLabel.fontColor = UIColor.whiteColor()
scoreLabel.fontName = "Avenir"
scoreLabel.fontSize = 25
scoreLabel.text = "0"
scoreLabel.position = CGPoint(x:CGRectGetMidX(frame) + 140, y: CGRectGetMidY(frame))
addChild(scoreLabel)
//////THE LOOP/////////////////////////////////////////////
let borderBody = SKPhysicsBody(edgeLoopFromRect: self.frame)
borderBody.friction = 0
self.physicsBody = borderBody
spawnPaddle()
spawnBottom()
}
override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
/* Called when a touch begins */
var touch = touches.anyObject() as UITouch
var touchLocation = touch.locationInNode(self)
if let body = physicsWorld.bodyAtPoint(touchLocation) {
if body.node?.name == PaddleCategoryName {
println("On the paddle")
isFingerOnPaddle = true
}
}
}
override func touchesMoved(touches: NSSet, withEvent event: UIEvent) {
if isFingerOnPaddle {
var touch = touches.anyObject() as UITouch
var touchLocation = touch.locationInNode(self)
var previousLocation = touch.previousLocationInNode(self)
var paddleX = paddle.position.x + (touchLocation.x - previousLocation.x)
paddleX = max(paddleX, paddle.size.width/2)
paddleX = min(paddleX, size.width - paddle.size.width/2)
paddle.position = CGPointMake(paddleX, paddle.position.y)
}
}
func random(x: Int) -> Int {
var y = arc4random_uniform(UInt32(x))
return Int(y)
}
func start(sender: AnyObject) {
if isBall == false {
spawnBall()
ball.physicsBody?.applyImpulse(CGVectorMake(12, 40))
println("ball")
}
}
override func touchesEnded(touches: NSSet, withEvent event: UIEvent) {
isFingerOnPaddle = false
}
func didBeginContact(contact: SKPhysicsContact) {
var firstBody: SKPhysicsBody
var secondBody: SKPhysicsBody
if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
firstBody = contact.bodyA
secondBody = contact.bodyB
} else {
firstBody = contact.bodyB
secondBody = contact.bodyA
}
func changeScene() {
let gameOverScene = GameOverScene(size: size)
gameOverScene.scaleMode = scaleMode
let reveal = SKTransition.flipHorizontalWithDuration(0.5)
view?.presentScene(gameOverScene, transition: reveal)
}
if firstBody.categoryBitMask == BallCategory && secondBody.categoryBitMask == BottomCategory {
println("Hit bottom.")
ball.physicsBody?.velocity = CGVectorMake(0, 0)
isBall = false
ball.removeFromParent()
score++
println(score)
scoreLabel.text = String(score)
isRunning = false
if score >= 3 {
ball.physicsBody?.velocity = CGVectorMake(0, 0)
isBall = false
ball.removeFromParent()
println("Game Over")
changeScene()
}
}
}
}