SpriteKit applyImpulse not affecting sprite

Question

I have a player node that is of type Skier that I want to move around the x-axis with a touch and drag similar to this tutorial . I added my player node to the scene and it has a physics body with isDynamic set to true, but for some reason when I touch and drag the player doesn't move. What am I doing wrong? Here is my GameScene and my Skier class:

Skier:

class Skier: SKSpriteNode {
    let playerTexture = SKTexture(imageNamed: "snowmanFancy_NE")
    let playerSize = CGSize(width: 24, height: 40)

    init () {
        super.init(texture: playerTexture, color: UIColor.clear, size: playerSize)
        self.name = "player"
        setPhysics()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func setPhysics(){
        self.anchorPoint = CGPoint(x: 0.5, y: 0.5)
        self.physicsBody? = SKPhysicsBody(rectangleOf: size)
        self.physicsBody?.categoryBitMask = PhysicsCategory.player
        self.physicsBody?.contactTestBitMask = PhysicsCategory.tree | 
        PhysicsCategory.rock | PhysicsCategory.cabin | PhysicsCategory.snowman | 
        PhysicsCategory.marker
        self.physicsBody?.collisionBitMask = 0
        self.physicsBody?.allowsRotation = false
        self.physicsBody?.angularDamping = 0
        self.physicsBody?.isDynamic = true
    }
}

GameScene:

class GameScene: SKScene, SKPhysicsContactDelegate {
    var lastTouch: CGPoint? = nil

    var world = SKNode()
    var cam = SKCameraNode()

    var player = Skier()
    let playerDefaultYInset : CGFloat = 350

    var sceneVelocity = CGVector(dx: 0, dy: -170)
    var zPositionCounter: CGFloat = 0

    override func didMove(to view: SKView) {
        //Set up the scene
        self.anchorPoint = CGPoint(x: 0.5, y: 0.5)
        backgroundColor = SKColor.white

        //Add top-level world node to the scene
        self.addChild(world)

        self.physicsWorld.contactDelegate = self

        //Add player to scene
        spawnPlayer()
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        let touch = touches.first
        if let location = touch?.location(in: self) {
            lastTouch = location
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        let touch = touches.first
        if let location = touch?.location(in: self) {
            lastTouch = location
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        lastTouch = nil
    }

    override func update(_ currentTime: TimeInterval) {
        // Only add an impulse if there's a lastTouch stored
        if let touch = lastTouch {
            let impulseVector = CGVector(dx: touch.x - player.position.x, dy: 0)
            // If myShip starts moving too fast or too slow, you can multiply impulseVector by a constant or clamp its range
            player.physicsBody?.applyImpulse(impulseVector)
        }
    }

    func spawnPlayer() {
        player.position = CGPoint(x: 0, y: (-self.frame.height / 2) + playerDefaultYInset)
        player.zPosition = CGFloat(Int.min)
        world.addChild(player)
    }
}

Answer 1

I figured out what I was doing wrong. When I set up my physics body for the Skier class, I assigned the physics body like this with an optional:

self.physicsBody? = SKPhysicsBody(rectangleOf: size)

so the physics body wasn't actually being assigned to the sprite. I fixed it by changing it to this:

self.physicsBody = SKPhysicsBody(rectangleOf: playerSize)

and now it works perfectly. That being said, for anyone else trying to achieve something similar to this effect with a finger drag moving a sprite around a scene, I ended up coming up with a much simpler solution. I have this in my touchesMoved method:

let touch = touches.first
    if let location = touch?.location(in: self) {
        let prev = touch?.previousLocation(in: self)
        let impulse = CGVector(dx: 0.02 * (location.x - (prev?.x)!), dy: 0)
        player.physicsBody?.applyImpulse(impulse)
}

And it works without having to worry about the update, touchesBegan, or touchesEnded methods at all. Much simpler and easier.