SpriteKit - RotateToAngle

Question

我有一个对象，我希望它能够不断向右旋转＆amp;左：

override func didMoveToView(view: SKView) {
    /* Setup your scene here */

// I start it facing left side
    object.zRotation = CGFloat(M_PI / 4)
}

 override func update(currentTime: CFTimeInterval) {
        /* Called before each frame is rendered */


        let rotateRight = SKAction.rotateToAngle(CGFloat(-M_PI / 4), duration: 2)
        let rotateLeft = SKAction.rotateToAngle(CGFloat(M_PI / 4), duration: 2)

        let sequence = SKAction.sequence([rotateRight, rotateLeft])

        object.runAction(SKAction.repeatActionForever(sequence))
    }

问题是，它只旋转到右侧然后完全停止，它从不向左旋转并按原样重复。