Asteroid Battle Game Keep Crashing - ios

Question

So I keep getting this error at random times during the play of the game, "fatal error: unexpectedly found nil while unwrapping an Optional value" in my asteroid battle game. I'll post the code here and if anyone could help figure it out I would appreciate it. If you don't understand any part you can ask me
import SpriteKit
import Darwin
struct PhysicsCatagory {
static let Asteroids : UInt32 = 1 //00000000000000000000000000000001
static let Bullet : UInt32 = 2 //0000000000000000000000000000010
static let Fighter : UInt32 = 3 //0000000000000000000000000000100
}
class GameScene: SKScene, SKPhysicsContactDelegate {
var Score = Int()
var scoreLabel = UILabel()
var Fighter = SKSpriteNode(imageNamed: "Fighter")
override func didMoveToView(view: SKView) {
/* Setup your scene here */
physicsWorld.contactDelegate = self
Fighter.position = CGPointMake(self.size.width / 2, self.size.height / 7)
Fighter.physicsBody = SKPhysicsBody(rectangleOfSize: Fighter.size)
Fighter.physicsBody?.affectedByGravity = false
Fighter.physicsBody?.categoryBitMask = PhysicsCatagory.Fighter
Fighter.physicsBody?.contactTestBitMask = PhysicsCatagory.Asteroids
Fighter.physicsBody?.dynamic = false
var Timer = NSTimer.scheduledTimerWithTimeInterval(0.25, target: self, selector: Selector("spawnBullets"), userInfo: nil, repeats: true)
var asteriodsTimer = NSTimer.scheduledTimerWithTimeInterval(0.35 , target: self, selector: Selector("spawnAsteroids"), userInfo: nil, repeats: true)
var furiousAsteriodsTimer = NSTimer.scheduledTimerWithTimeInterval(0.9 , target: self, selector: Selector("spawnFuriousAsteroids"), userInfo: nil, repeats: true)
self.addChild(Fighter)
scoreLabel.text = "\(Score)"
scoreLabel = UILabel(frame: CGRect(x: 0, y: 0, width: 200, height: 40))
scoreLabel.backgroundColor = UIColor(red: 0.2, green: 0.2, blue: 0.2, alpha: 0.3)
scoreLabel.textColor = UIColor.whiteColor()
self.view?.addSubview(scoreLabel)
}
func didBeginContact(contact: SKPhysicsContact) {
let firstBody : SKPhysicsBody = contact.bodyA
let secondBody : SKPhysicsBody = contact.bodyB
if ((firstBody.categoryBitMask == PhysicsCatagory.Asteroids) && (secondBody.categoryBitMask == PhysicsCatagory.Bullet) || (firstBody.categoryBitMask == PhysicsCatagory.Bullet) && (secondBody.categoryBitMask == PhysicsCatagory.Asteroids)){
bulletHitAsteroids(firstBody.node as! SKSpriteNode, Bullet: secondBody.node as! SKSpriteNode)
}
}
func bulletHitAsteroids(Asteroids: SKSpriteNode, Bullet: SKSpriteNode){
Asteroids.removeFromParent()
Bullet.removeFromParent()
Score++
scoreLabel.text = "\(Score)"
}
func bulletHitFuriousAsteroids(FuriousAsteroids: SKSpriteNode, Bullet: SKSpriteNode){
FuriousAsteroids.removeFromParent()
Bullet.removeFromParent()
Score = Score + 2
scoreLabel.text = "\(Score)"
}
func spawnBullets(){
let Bullet = SKSpriteNode(imageNamed: "Bullet")
Bullet.zPosition = -5
Bullet.position = CGPointMake(Fighter.position.x, Fighter.position.y)
let action = SKAction.moveToY(self.size.height + 30, duration: 0.9)
let actionDone = SKAction.removeFromParent()
Bullet.runAction(SKAction.sequence([action, actionDone]))
Bullet.physicsBody = SKPhysicsBody(rectangleOfSize: Bullet.size)
Bullet.physicsBody?.categoryBitMask = PhysicsCatagory.Bullet
Bullet.physicsBody?.contactTestBitMask = PhysicsCatagory.Asteroids
Bullet.physicsBody?.affectedByGravity = false
Bullet.physicsBody?.dynamic = false
self.addChild(Bullet)
}
func spawnAsteroids(){
let Asteroids = SKSpriteNode(imageNamed: "Asteroid")
let minValue = self.size.width / 8
let maxValue = self.size.width - 20
let spawnPoint = UInt32(maxValue - minValue)
Asteroids.position = CGPoint(x: CGFloat(arc4random_uniform(spawnPoint)) , y: self.size.height)
Asteroids.physicsBody = SKPhysicsBody(rectangleOfSize: Asteroids.size)
Asteroids.physicsBody?.categoryBitMask = PhysicsCatagory.Asteroids
Asteroids.physicsBody?.contactTestBitMask = PhysicsCatagory.Bullet
Asteroids.physicsBody?.affectedByGravity = false
Asteroids.physicsBody?.dynamic = true
let action = SKAction.moveToY(-50, duration: 2.5)
let actionDone = SKAction.removeFromParent()
Asteroids.runAction(SKAction.sequence([action, actionDone]))
self.addChild(Asteroids)
}
func spawnFuriousAsteroids(){
let FuriousAsteroids = SKSpriteNode(imageNamed: "FuriousAsteroid")
let minValue = self.size.width / 8
let maxValue = self.size.width - 20
let spawnPoint = UInt32(maxValue - minValue)
FuriousAsteroids.position = CGPoint(x: CGFloat(arc4random_uniform(spawnPoint)) , y: self.size.height)
FuriousAsteroids.physicsBody = SKPhysicsBody(rectangleOfSize: FuriousAsteroids.size)
FuriousAsteroids.physicsBody?.categoryBitMask = PhysicsCatagory.Asteroids
FuriousAsteroids.physicsBody?.contactTestBitMask = PhysicsCatagory.Bullet
FuriousAsteroids.physicsBody?.affectedByGravity = false
FuriousAsteroids.physicsBody?.dynamic = true
let action = SKAction.moveToY(-50, duration: 1.5)
let actionDone = SKAction.removeFromParent()
FuriousAsteroids.runAction(SKAction.sequence([action, actionDone]))
self.addChild(FuriousAsteroids)
}
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
/* Called when a touch begins */
for touch in touches {
let location = touch.locationInNode(self)
Fighter.position.x = location.x
}
}
override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
for touch in touches {
let location = touch.locationInNode(self)
Fighter.position.x = location.x
}
}
override func update(currentTime: CFTimeInterval) {
/* Called before each frame is rendered */
}
}

Answer 1

It is crashing because one of the bodies doesn't have its node. When crash happen, try to type something like this in debugger console :
po firstBody.node, or po secondBody.node. One of these two will be nil.
This is happening when more than two bodies make contact as in your example, where you can have a situation where bullet and a two asteroids might be in a contact at the same time. Because SpriteKit can check for a contact only between two bodies at the time, something like this will happen:
didBeginContact is invoked with two physicsBodies passed in (bullet and first asteroide)
now, you are force unwrapping nodes associated with those bodies and removing the asteroid and the bullet from its parent
then, because there are more contacts occurred
didBeginContact is invoked again, with another two physics bodies, but one of those physicsBodies is bullet's physics body again. Another body is , let say furious asteroid.
now, again you are force unwrapping nodes associated with those two physics bodies, but one of them (bullet) is nil.
Solution would be something like this in your didBeginContact method:
if let firstNode = firstBody.node as? SKSpriteNode, let secondNode = secondBody.node as? SKSpriteNode {
bulletHitAsteroids(firstNode, Bullet: secondNode)
}
This way, one bullet will destroy only one asteroid. Which I guess is what you want and what make sense after all.