SKPhysicsContactDelegate

GameScene.swift

// omitted
class GameScene: SKScene, SKPhysicsContactDelegate {
    // omitted
    
    override func didMoveToView(view: SKView) {
        // tell the physics world that the class the implements
        // the SKPhysicsContactDelegate is the GameScene
        physicsWorld.contactDelegate = self
        
        setupFloor()
        setupPlayer()
    }
    
    func setupPlayer() {
        // omitted
        
        // notify when the player collides
        player.physicsBody?.contactTestBitMask = Physics.Character
        
        // this add the player to the scene in order to appear in the screen
        addChild(player)
    }
    
    func setupFloor() {
        // omitted
        
        // notify then the floor collides
        floor.physicsBody?.collisionBitMask = Physics.Floor
        
        // this add the floor to the scene in order to appear in the screen
        addChild(floor)
    }
    
    func spawEnemy(){
        // omitted
        
        // notify when the enemy collides
        enemy.physicsBody?.contactTestBitMask = Physics.Character
        
        // add the enemy to the scene
        addChild(enemy)
        
        // store the enemy to use later
        enemies.append(enemy)
    }
}