didBeginContact not being called - ios

Question

I'm trying to create a program that prints out something whoever my spaceship goes over a circle, but it's not printing anything when I put the spaceship over the circle. Did I build my didBeginContact method wrong? Did I set up the BitMasks wrong?
import SpriteKit
class GameScene: SKScene {
var spaceship: SKNode!
var circ: SKNode!
override func didMoveToView(view: SKView) {
self.physicsWorld.gravity = CGVector(dx: 0, dy: 0)
spaceship = SKSpriteNode(imageNamed: "Spaceship")
spaceship.setScale(0.4)
spaceship.position.x = self.frame.width/2
spaceship.position.y = spaceship.frame.height/2
spaceship.physicsBody = SKPhysicsBody(circleOfRadius: spaceship.frame.height/2)
spaceship.physicsBody?.categoryBitMask = 1
spaceship.physicsBody?.contactTestBitMask = 2
spaceship.physicsBody?.collisionBitMask = 0
spaceship.physicsBody?.dynamic = true
circ = SKShapeNode(circleOfRadius: 50)
circ.position.y = self.frame.height/2
circ.position.x = self.frame.width/2
circ.physicsBody = SKPhysicsBody(circleOfRadius: 50)
circ.physicsBody?.categoryBitMask = 2
circ.physicsBody?.contactTestBitMask = 1
circ.physicsBody?.collisionBitMask = 0
circ.physicsBody?.dynamic = true
self.addChild(circ)
self.addChild(spaceship)
}
func didBeginContact(contact: SKPhysicsContact){
println("colliding!")
}
override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
for touch: AnyObject in touches {
let location = touch.locationInNode(self)
spaceship.position = location
}
}
override func touchesMoved(touches: NSSet, withEvent event: UIEvent) {
for touch: AnyObject in touches {
let location = touch.locationInNode(self)
spaceship.position = location
}
}
}

Answer 1

You need to declare yourself as the contact delegate of your physics world:
// add conformance to SKPhysicsContactDelegate:
class GameScene: SKScene, SKPhysicsContactDelegate {
// ...
override func didMoveToView(view: SKView) {
self.physicsWorld.gravity = CGVector(dx: 0, dy: 0)
// set as delegate:
self.physicsWorld.contactDelegate = self
// ..
}
// should be called now
func didBeginContact(contact: SKPhysicsContact){
println("colliding!")
}
}