Why can't I cast ContactBody to a custom SKNode in SpriteKit - ios

Question

I am having trouble trying to cast a ContactBody to a custom SKNode. The implementation looks like this:
case PhysicsCategory.player | PhysicsCategory.spring:
if contact.bodyA.categoryBitMask == PhysicsCategory.spring{
if let theSpring = contact.bodyA.node as? Spring
{
theSpring.printMsg()
}else{
print("can't cast bodyA to spring")
}
}else{
if let theSpring = contact.bodyB.node as? Spring
{
theSpring.printMsg()
}else{
print("can't cast bodyB to spring")
}
}
When contact is made between the player and the spring, I get the message "can't cast bodyA to spring." The spring class looks like this:
import SpriteKit
class Spring: SKNode {
var impulse: Int
var sprite: SKSpriteNode
var textureAtlas: SKTextureAtlas
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
init (launchSpeed: Int){
impulse = launchSpeed
textureAtlas = SKTextureAtlas(named: "NonTiledItems")
sprite = SKSpriteNode(texture: textureAtlas.textureNamed("spring01"))
sprite.physicsBody = SKPhysicsBody(rectangleOfSize: sprite.size)
sprite.physicsBody!.categoryBitMask = PhysicsCategory.spring // could we make this button?
sprite.physicsBody!.allowsRotation = false
sprite.physicsBody!.dynamic = false
sprite.physicsBody!.affectedByGravity = false
sprite.physicsBody!.friction = 0.6
sprite.physicsBody!.collisionBitMask = PhysicsCategory.player
super.init()
addChild(sprite)
}
func printMsg(){
print("contact Made")
}
}
I cannot figure out why the ContactBody will not cast to the Spring class since spring inherits from SKNode. If anyone has any advice, it would be greatly appreciated.

Answer 1

your physics body is attached to an SKSpriteNode, not the Spring. You need to remove the skspritenode reference, you need Spring to be a child of SKSpriteNode, and you need to write a convenience init like this:
convenience init (launchSpeed: Int)
{
self.SKSpriteNode(texture: SKTextureAtlas(named: "NonTiledItems").textureNamed("spring01"))
impulse = launchSpeed
self.physicsBody = SKPhysicsBody(rectangleOfSize: self.size)
self.physicsBody!.categoryBitMask = PhysicsCategory.spring // could we make this button?
self.physicsBody!.allowsRotation = false
self.physicsBody!.dynamic = false
self.physicsBody!.affectedByGravity = false
self.physicsBody!.friction = 0.6
self.physicsBody!.collisionBitMask = PhysicsCategory.player
}