我无法将球SKSpriteNode显示在辅助View Controller的UIImage（Xcode / Swift 2）上

Question

I have a button on my first view controller that leads to the second view controller. When the second view controller appears, a ball image is supposed to appear and it's code is supposed to run. I seem to be having a little bit of trouble figuring out why the image isn't appearing. Any help would be greatly appreciated!

---

import UIKit
import SpriteKit

class GameViewController: UIViewController {
    @IBOutlet weak var startButton: UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()

        if let scene = gamePlay(fileNamed:"gamePlay") {
            // Configure the view.
            let skView = self.view as! SKView
            skView.showsFPS = true
            skView.showsNodeCount = true

            /* Sprite Kit applies additional optimizations to improve rendering performance */
            skView.ignoresSiblingOrder = true

            /* Set the scale mode to scale to fit the window */
            scene.scaleMode = .AspectFill

            skView.presentScene(scene)
        }
    }

    override func shouldAutorotate() -> Bool {
        return true
    }

    override func supportedInterfaceOrientations() -> UIInterfaceOrientationMask {
        if UIDevice.currentDevice().userInterfaceIdiom == .Phone {
            return .AllButUpsideDown
        } else {
            return .All
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Release any cached data, images, etc that aren't in use.
    }

    override func prefersStatusBarHidden() -> Bool {
        return true
    }
}

---

import SceneKit
import SpriteKit

class gamePlayController: UIViewController {

}

class gamePlay: SKScene, SKPhysicsContactDelegate {
    let skyColor = SKColor(red: 0, green: 191, blue: 255, alpha: 1)
    var blueBall:SKSpriteNode!

    override func didMoveToView(view: SKView) {

        self.backgroundColor = skyColor
        self.physicsWorld.gravity = CGVectorMake(0.0, -5.0)
        self.physicsWorld.contactDelegate = self

        blueBall = SKSpriteNode( imageNamed: "ball")
        blueBall.position = CGPoint(x: CGRectGetMidX(self.frame), y: CGRectGetMidY(self.frame))
        blueBall.physicsBody = SKPhysicsBody(circleOfRadius: blueBall.size.width / 1.5 )

        blueBall.physicsBody!.dynamic = true
        blueBall.physicsBody!.allowsRotation = false

        self.addChild(blueBall)
    }

    override func touchesBegan(touches: Set<UITouch> , withEvent event: UIEvent?) {
        self.blueBall.physicsBody?.velocity = CGVectorMake(35, 0)
        self.blueBall.physicsBody?.applyImpulse(CGVectorMake(4, 10))
    } 
}

Answer 1

Looks like position is wrong. Try this code

        blueBall.position = CGPoint(x: CGRectGetMidX(self.bounds), y: CGRectGetMidY(self.bounds))

Answer 2

I fixed the issue. I needed to write my backgroundImage as an SKSpriteNode and set the zPosition accordingly.