Could not create physics body - Swift

问题:

I have a Swift file called ChainsawMaker.swift which I want to use to create chainsaws throughout my game. When I call instances of this and add it to my game, the chainsaws and it's physics body get added to the game perfectly - except for an error that pops up in the console: "Physics Body: Could not create physics body". Here is the code for ChainsawMaker.swift:

import SpriteKit

class ChainsawMaker: SKSpriteNode {

func longChainsawCreator2 () -> SKSpriteNode {

    //LONG CHAINSAW
    let longChainsawWidth = size.width/3
    let longChainsawHeight = size.height*0.20

    let chainsaw = SKSpriteNode ()


    chainsaw.zPosition = 13
    chainsaw.anchorPoint = CGPoint(x: 0.5, y: 0.5)
    chainsaw.size = CGSize(width: longChainsawWidth, height: longChainsawHeight)
    let textures = [SKTexture(imageNamed: "chainsaw1"), SKTexture(imageNamed: "chainsaw2")]
    let animation = SKAction.animateWithTextures(textures, timePerFrame: 0.1)
    let runSawAnimation = SKAction.repeatActionForever(animation)
    chainsaw.runAction(runSawAnimation)




    var offsetX = chainsaw.frame.size.width/2;
    var offsetY = chainsaw.frame.size.height/2 + chainsaw.size.height/13;

    var path = CGPathCreateMutable();


    CGPathMoveToPoint(path, nil, chainsaw.frame.size.width/2 - offsetX, chainsaw.frame.size.height - offsetY);
    CGPathAddLineToPoint(path, nil, 0 + chainsaw.frame.size.width/12 - offsetX, chainsaw.frame.size.height - offsetY);
    CGPathAddLineToPoint(path, nil, 0 - offsetX, chainsaw.frame.size.height - chainsaw.size.height/2 - offsetY);
    CGPathAddLineToPoint(path, nil, 0 + chainsaw.size.width/28 - offsetX, chainsaw.frame.size.height - chainsaw.size.height/2 - chainsaw.size.height/6 - offsetY);

    CGPathAddLineToPoint(path, nil, 0 + chainsaw.frame.size.width/12 - offsetX, 0 + chainsaw.size.height/8 - offsetY);
    CGPathAddLineToPoint(path, nil, chainsaw.size.width - chainsaw.frame.size.width/12 - offsetX, 0 + chainsaw.size.height/8 - offsetY);

    CGPathAddLineToPoint(path, nil, chainsaw.size.width - offsetX, chainsaw.frame.size.height - chainsaw.size.height/2 - offsetY);

    CGPathAddLineToPoint(path, nil, chainsaw.size.width - chainsaw.frame.size.width/16 - offsetX, chainsaw.size.height - offsetY);


    CGPathCloseSubpath(path);

    chainsaw.physicsBody = SKPhysicsBody(polygonFromPath: path)


    chainsaw.physicsBody?.dynamic = true
    chainsaw.physicsBody?.categoryBitMask = chainsawCategory
    chainsaw.physicsBody?.contactTestBitMask = boCategory
    chainsaw.physicsBody?.collisionBitMask = noneCategory

    return chainsaw
}

}

And then this is how I create an instance of a chainsaw in my GamePlayScene.swift:

import SpriteKit

class GameScene: SKScene, SKPhysicsContactDelegate {
    var longChainsaw = ChainsawMaker()

    override func didMoveToView(view: SKView) {
     longChainsaw.longChainsawCreator2()
    longChainsaw.position = CGPoint(x: chainsawHolder.size.width/2, y:   chainsawHolder.size.height/2 - boHeight/2)