Swift: Physics Body Collision Bad Instruction Error - swift

Question

When I run this code the first CollisionWithplayer line gives me a bad instruction error. The error doesn't appear every time, only every once in a while with no similar conditions to identify what is causing it.
func didBeginContact(contact: SKPhysicsContact) {
let firstBody : SKPhysicsBody = contact.bodyA
let secondBody : SKPhysicsBody = contact.bodyB
if ((firstBody.categoryBitMask == PhysicsCategory.Goblin) && (secondBody.categoryBitMask == PhysicsCategory.Bullet) ||
(firstBody.categoryBitMask == PhysicsCategory.Bullet) && (secondBody.categoryBitMask == PhysicsCategory.Goblin))
{
CollisionWithBullet(firstBody.node as! SKSpriteNode, Bullet: secondBody.node as! SKSpriteNode)
}
else if ((firstBody.categoryBitMask == PhysicsCategory.Goblin) && (secondBody.categoryBitMask == PhysicsCategory.player) ||
(firstBody.categoryBitMask == PhysicsCategory.player) && (secondBody.categoryBitMask == PhysicsCategory.Goblin)){
CollisionWithplayer(firstBody.node as! SKSpriteNode, player: secondBody.node as! SKSpriteNode)
}
func CollisionWithBullet(Goblin: SKSpriteNode, Bullet:SKSpriteNode){
Goblin.removeFromParent()
Bullet.removeFromParent()
score += 1
ScoreLbl.text = "\(score)"
var explosion = SKEmitterNode(fileNamed: "Goblin Death Animation.sks")
explosion!.particlePosition = Goblin.position
self.addChild(explosion!)
var fire = SKEmitterNode(fileNamed: "Goblin Death Animation 2.sks")
fire!.particlePosition = Goblin.position
self.addChild(fire!)
}
func CollisionWithplayer(Goblin: SKSpriteNode, player: SKSpriteNode){
let ScoreDefault = NSUserDefaults.standardUserDefaults()
ScoreDefault.setValue(score, forKey: "Score")
ScoreDefault.synchronize()
if (score > Highscore){
let HighscoreDefault = NSUserDefaults.standardUserDefaults()
HighscoreDefault.setValue(score, forKey: "Highscore")
}
Goblin.removeFromParent()
player.removeFromParent()
self.view?.presentScene(EndScene())
ScoreLbl.removeFromSuperview()
}

Answer 1

I assume you get an error because your code doesn't treat the case where 1 collision causes the didBeginContact method to fire more than once (collision happened at 2 points of same node)
I would rewrite your code like this to avoid such a case (using optionals). Furthermore I slightly rewrote it so you don't have to write 2 if statements for each collision.
func didBeginContact(contact: SKPhysicsContact) {
let firstBody: SKPhysicsBody
let secondBody: SKPhysicsBody
if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
firstBody = contact.bodyA
secondBody = contact.bodyB
} else {
firstBody = contact.bodyB
secondBody = contact.bodyA
}
if (firstBody.categoryBitMask == PhysicsCategory.Goblin) && (secondBody.categoryBitMask == PhysicsCategory.Bullet) {
collisionWithBullet(firstBody.node as? SKSpriteNode, bullet: secondBody.node as? SKSpriteNode)
}
if (firstBody.categoryBitMask == PhysicsCategory.Goblin) && (secondBody.categoryBitMask == PhysicsCategory.player) {
collisionWithPlayer(firstBody.node as? SKSpriteNode, player: secondBody.node as? SKSpriteNode)
}
}
func collisionWithBullet(goblin: SKSpriteNode?, bullet:SKSpriteNode?){
guard let goblin = goblin, bullet = bullet else { return }
goblin.removeFromParent()
bullet.removeFromParent()
score += 1
scoreLbl.text = "\(score)"
if let explosion = SKEmitterNode(fileNamed: "Goblin Death Animation.sks") {
explosion.particlePosition = goblin.position
self.addChild(explosion)
}
if let fire = SKEmitterNode(fileNamed: "Goblin Death Animation 2.sks") {
fire.particlePosition = goblin.position
self.addChild(fire)
}
}
func collisionWithPlayer(goblin: SKSpriteNode?, player: SKSpriteNode?){
guard let goblin = goblin, player = player else { return }
let scoreDefault = NSUserDefaults.standardUserDefaults()
scoreDefault.setValue(score, forKey: "Score")
// synchronised not needed anymore
if (score > highscore){
let highscoreDefault = NSUserDefaults.standardUserDefaults()
highscoreDefault.setValue(score, forKey: "Highscore")
}
goblin.removeFromParent()
player.removeFromParent()
self.view?.presentScene(EndScene())
scoreLbl.removeFromSuperview()
}
Please also follow the swift guidlines, your methods and properties should start will small letters not will capital letters.
Hope this helps