Why does SKLabelNode increment too much on Contact? (Swift) - swift

Question

I am trying to have my Label to increment +1 every time a sprite makes contact with a Contact node, but it increments by large numbers like +23. I think what is happening is that its taking into account every millisecond that the sprite is touching the node, but i don't know how to fix it.
Here is my Label node code within DidMoveToView:
score = 0
scoreLabelNode = SKLabelNode(fontNamed:"[z] Arista Light")
scoreLabelNode.position = CGPointMake(self.frame.size.width/2, self.frame.size.height/4)
scoreLabelNode.zPosition = 100
scoreLabelNode.fontSize = 500
scoreLabelNode.alpha = 0.03
scoreLabelNode.text = String(score)
self.addChild(scoreLabelNode)
here is my contact node:
var contactNode = SKNode()
contactNode.position = CGPoint(x: self.frame.size.width + asteroidTexture.size().height / 15 + rocket.size.width, y: 0.0)
contactNode.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake( asteroid.size.width/16, self.frame.size.height*2 ))
contactNode.physicsBody?.dynamic = false
contactNode.physicsBody?.categoryBitMask = scoreCategory
contactNode.physicsBody?.contactTestBitMask = rocketCategory
contactNode.runAction(asteroidsMoveAndRemove)
moving.addChild(contactNode)
and here is my code where when my rocket sprite makes contact with the contactNode it increments:
func didBeginContact(contact: SKPhysicsContact) {
if moving.speed > 0 {
if ( contact.bodyA.categoryBitMask & scoreCategory ) == scoreCategory || ( contact.bodyB.categoryBitMask & scoreCategory ) == scoreCategory {
// Rocket has contact with score entity
score++
scoreLabelNode.text = String(score)
println("HIT")
}
else{
gameOver()
}
}
'moving' is when my asteroid sprites are moving, the contact nodes move with it

Answer 1

It's probably not every millisecond, but instead every frame, and that's why you likely end up with numbers like +23 (The collision is taking place for a 1/3 of a second and if it's running at 60 FPS that is about 20 or so frames).
One thing you could do is subclass SKNode into an actual ContactNode class that has a property hasBeenStruck that is initially set to false or something to that extent.
Then when you check contact, you first check to see if hasBeenStruck is false. If it is, register the hit and update the score and then set that ContactNode's hasBeenStruck property to true. This way, on the next 20 or so checks to see if contact has happened, it won't keep updating the label because the if condition has failed.
However, if your game allows a user to hit the same ContactNode twice and get score both times, this isn't a complete solution. If that is the case, you could use a timer or "invincibility" period for the given ContactNode.