SKPhysicsContact not contacting enemy with bullet - swift

Question

I already have my categorybitmasks setup hopefully correctly but my code below should have my bullet and enemy contact and then remove each other. Nothing happens, they just collide and still stay on the screen
func didBeginContact(contact: SKPhysicsContact!) {
var firstBody: SKPhysicsBody!
var 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 & bulletCategory) != 0 &&
(secondBody.categoryBitMask & enemyCategory) != 0 {
destroyEnemy(bullet: firstBody.node as! SKSpriteNode, enemy: secondBody.node as! SKSpriteNode)
}
}
func destroyEnemy(bullet: SKSpriteNode, enemy: SKSpriteNode) {
bullet.removeFromParent()
enemy.removeFromParent()
}
enemy.physicsBody?.categoryBitMask = CollisionTypes.enemy.rawValue
enemy.physicsBody?.contactTestBitMask = CollisionTypes.bullet.rawValue
enemy.physicsBody?.collisionBitMask = CollisionTypes.bullet.rawValue
bullet.physicsBody?.categoryBitMask = CollisionTypes.bullet.rawValue
bullet.physicsBody?.contactTestBitMask = CollisionTypes.enemy.rawValue
bullet.physicsBody?.collisionBitMask = CollisionTypes.enemy.rawValue

Answer 1

This isn't an answer per se, but is a bit long for a comment:
In your didBegin you have:
if (firstBody.categoryBitMask & bulletCategory) != 0 &&
(secondBody.categoryBitMask & enemyCategory) != 0 {
destroyEnemy(bullet: firstBody.node as! SKSpriteNode, enemy: secondBody.node as! SKSpriteNode)
What happens if firstBody is the enemy and secondBody is the bullet? It would appear that the code to be run when the contact occurs won't fire. Without seeing your categoryBitMask definitions we won't know because you appear to be assigning first and second body in ascending order of the categoryBitMask value.
You could confirm if this is working with another print inside the if block.
I've never really liked this form of didBegin and I personally find this style more readable:
func didBegin(_ contact: SKPhysicsContact) {
print("didBeginContact entered for \(String(describing: contact.bodyA.node!.name)) and \(String(describing: contact.bodyB.node!.name))")
let contactMask = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
switch contactMask {
case bulletCategory | enemyCategory:
print("bullet and enemy have contacted.")
let bulletNode = contact.bodyA.categoryBitMask == bulletCategory ? contact.bodyA.node : contact.bodyB.node
let enemyNode = contact.bodyA.categoryBitMask == enemyCategory ? contact.bodyA.node : contact.bodyB.node
destroyEnemy(bullet: bulletNode, enemy: enemyNode)
case playerCategory | enemyCategory:
// Handle player/Enemy collisions
default:
print("Some other contact occurred")
}