Single collisions being detected multiple times - ios

Question

I've read similar questions posted here, but none of them fully address my problem.
I've only been working with iOS for a few months.
My collisions are working 90% of the time, but occasionally I'm getting collisions with same object. This should never happen because one of the 2 objects should explode.
Sometimes this leads to fatal crashes, seemingly because it tries to run the subsequent code after its already been executed.
Basically when the ship has a shield I want the asteroid to explode rather than the ship. I have put in the "if bonus == 0" statement to accomplish this.
I've posted the relevant code, if you need more, please let me know.
Have I over complicated the code? Or should I be taking another approach?
enum PhysicsCategory : UInt32 {
case None = 0
case objectGroup = 1
case birdGroup = 2
case shieldGroup = 4
case gapGroup = 8
case boundaryGroup = 16
case bonusGroup = 32
}
....
func didBeginContact(contact: SKPhysicsContact) {
if bonus == 0 {
let contactMask = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
switch contactMask {
....
case PhysicsCategory.birdGroup.rawValue | PhysicsCategory.objectGroup.rawValue:
if contact.bodyA.categoryBitMask == PhysicsCategory.birdGroup.rawValue {
gameOverActions()
} else if contact.bodyB.categoryBitMask == PhysicsCategory.birdGroup.rawValue {
gameOverActions()
}
default:
fatalError("other collision: \(contactMask)")
}
} else if bonus > 0 {
println("Bonus > 0")
let contactMask = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
switch contactMask {
....
case PhysicsCategory.birdGroup.rawValue | PhysicsCategory.objectGroup.rawValue:
if contact.bodyA.categoryBitMask == PhysicsCategory.birdGroup.rawValue {
let secondBody = contact.bodyB.node
let asteroidExplosionNode = secondBody?.position
//asteroidExplosion()
let asteroidExplosionEmitter3 = SKEmitterNode(fileNamed: "explosionSmoke.sks")
asteroidExplosionEmitter3.position = asteroidExplosionNode!
asteroidExplosionEmitter3.name = "asteroidExplosionEmitter3"
asteroidExplosionEmitter3.zPosition = 25
asteroidExplosionEmitter3.targetNode = self
movingObjects.addChild(asteroidExplosionEmitter3)
secondBody?.removeFromParent()
bonus--
bonusUsed++
bonusIndicator.text = "x\(bonus)"
bonusIndicatorShadow.text = "x\(bonus)"
if bonus >= 1 {
shieldAnimate()
} else if bonus == 0 {
shield.removeFromParent()
}
} else if contact.bodyB.categoryBitMask == PhysicsCategory.birdGroup.rawValue {
let secondBody = contact.bodyA.node
let asteroidExplosionNode = secondBody?.position
//asteroidExplosion()
let asteroidExplosionEmitter3 = SKEmitterNode(fileNamed: "explosionSmoke.sks")
asteroidExplosionEmitter3.position = asteroidExplosionNode!
asteroidExplosionEmitter3.name = "asteroidExplosionEmitter3"
asteroidExplosionEmitter3.zPosition = 25
asteroidExplosionEmitter3.targetNode = self
movingObjects.addChild(asteroidExplosionEmitter3)
secondBody?.removeFromParent()
bonus--
bonusUsed++
bonusIndicator.text = "x\(bonus)"
bonusIndicatorShadow.text = "x\(bonus)"
if bonus >= 1 {
shieldAnimate()
} else if bonus == 0 {
shield.removeFromParent()
}
}
default:
fatalError("other collision: \(contactMask)")
}
}
}

Answer 1

Since you are removing the node on collision you can check if the parent is nil, before executing the rest of the code.
let secondBody = contact.bodyB.node
if secondBody?.parent != nil {
// Asteroid explosion and bonus code.
}