落球动画不起作用（Swift）

Question

该代码应该将球从屏幕顶部放到底部。 并且，一旦触摸到屏幕底部，它就应该回到屏幕顶部。 它不会移到顶部，并且会停止移动。 我希望它是一个连续的循环，每次触到底部时都会重置ball.y位置。

import SpriteKit

class GameScene: SKScene {
    let ball = SKShapeNode(circleOfRadius: 20)
    let label = SKLabelNode(fontNamed: "Futura")
    let movingObjects = SKSpriteNode()

    override func didMoveToView(view: SKView) {
        let sceneBody = SKPhysicsBody(edgeLoopFromRect: self.frame)
        self.physicsBody = sceneBody

        //Ball Transition
        let ballTransition = SKAction.sequence([SKAction.fadeInWithDuration(1)])
        ball.runAction(ballTransition)

        //Ball function
        ball.fillColor = SKColor.redColor()

        ball.physicsBody = SKPhysicsBody(circleOfRadius: 25)
        ball.physicsBody?.affectedByGravity = false

        //Ball Movement
        ball.position = CGPoint(x: self.frame.size.width/2, y: CGFloat(self.frame.size.height*1))

        ballMovement()

        movingObjects.addChild(ball)

        self.addChild(label)
    }

    func ballMovement() {
        let moveBall = SKAction.moveToY(self.frame.size.height*0, duration: 3)
        let removeBall = SKAction.removeFromParent()
        let moveAndRemove = SKAction.sequence([moveBall, removeBall])
        ball.runAction(moveAndRemove)

        //Label Sprite
        label.position = CGPoint(x: CGRectGetMidX(self.frame), y: CGRectGetMidY(self.frame))
        label.fontColor = SKColor.redColor()
        label.fontSize = 30
    }

    override func update(currentTime: CFTimeInterval) {
        /* Called before each frame is rendered */
        label.text = "\(ball.position.y)"

        if ball.position.y < 26 {
            ball.position = CGPoint(x: self.frame.size.width/2, y: CGFloat(self.frame.size.height*1))
        }
    }
}

Answer 1

随着程序变得越来越复杂，在动作中将球从其父对象中移除并仍然在其他位置对其进行操作将变得非常脆弱。 为什么不只用动作来做所有事情，而让Sprite Kit担心呢？

 let moveBall = SKAction.moveToY(0, duration: 3)
 let goBackUp = SKAction.moveToY(self.frame.size.height, duration:0)
 let keepFalling = SKAction.sequence([moveBall, goBackUp])
 ball.runAction(SKAction.repeatActionForever(keepFalling))