如何让sprite在SwiftKit中永远上下移动

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")
}