如何让sprite在SwiftKit中永远上下移动

我试图让精灵永远上下移动,我尝试使用“if语句”检查位置是否……而不是再次向上移动.但它不起作用.
我真的很感激一些帮助,谢谢！
这是代码.

var Ground = SKSpriteNode()
var Ground2 = SKSpriteNode()

override func didMoveToView(view: SKView) {
    Move()
}

func Move(){
    let action = SKAction.moveToY(self.frame.height / 2 - 360, duration: 5.0)
    Ground.runAction(SKAction.repeatActionForever(action))

    let action2 = SKAction.moveToY(self.frame.height / 2 + 140, duration: 5.0)
    Ground2.runAction(SKAction.repeatActionForever(action2))
}

您可以使用动作序列：

override func didMoveToView(view: SKView) {

    let sprite = SKSpriteNode(color: SKColor.purpleColor(), size: CGSize(width: 100, height: 10))

    sprite.position = CGPoint(x: CGRectGetMidX(frame), y: CGRectGetMidY(frame))

    addChild(sprite)

    let moveUp = SKAction.moveByX(0, y: 200, duration: 2)

    let sequence = SKAction.sequence([moveUp, moveUp.reversedAction()])

    sprite.runAction(SKAction.repeatActionForever(sequence), withKey:  "moving")
}