The image I set to the background in SpriteKit is not displayed.

import SpriteKit

classGameScene:SKScene{

    override func DidMoveToView (view:SKView) {
        letbackGround=SKSpriteNode(imageNamed: "haikei.png")
        backGround.position = CGPoint (x:self.size.width*0.5, y:self.size.height*0.5)
        backGround.size = self.size
        self.addChild (backGround)
    }
}

import UIKit import SpriteKit

classGameViewController:UIViewController {

    override func viewDidLoad(){
        super.viewDidLoad()

        letscene=GameScene()
        let view=self.view as!SKView
        view.showsFPS=true
        view.showsNodeCount=true
        scene.size=view.frame.size

        view.presentScene(scene)
    }
}