Swift/SpriteKit - Collisions and Objects

Question

I have a class called Item, and inside there is an instance variable called itemNode which is of type SKSpriteNode. In my GameScene class, when I create an instance of Item I create a physics body that is given to the Item's itemNode. In my collision detection system, when my character's physics body collides with the itemNode's physics body, I want to preform a function on the Item object whose node's physics body just collided. However, the collision system only returns to physics body. How do I access the Item object given only the physics body of the node?

Answer 1

The SKPhyicsBody class has a node property which points to the SKNode instance it is attached to.

Your collision detection code can look something like this:

func didBeginContact(contact: SKPhysicsContact) {

    var item: SKSpriteNode
    var character: SKSpriteNode

    //Change this on the basis of the order of your categoryBitMask values
    if (contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask)
    {
        item = contact.bodyA.node as SKSpriteNode
        character = contact.bodyB.node as SKSpriteNode
    }
    else
    {
        item = contact.bodyB.node as SKSpriteNode
        character = contact.bodyA.node as SKSpriteNode
    }

    //Perform necessary operations on item and character
}

EDIT: In order to get access to the Item instance that declares the node, you will have to store a variable within the node which points to the Item instance. For this, you can either subclass SKSpriteNode and include a property, or use the userData property of SKNode

Subclassing:

//New Class
class ItemNode: SKSpriteNode {

    static var itemInstance
}

//In the Item class declare the itemNode using this class
let itemNode = ItemNode()
itemNode.itemInstance = self

UserData property:

item.userData = NSMutableDictionary(object: self, forKey: "ItemInstance"))