如何使不同的节点从设定位置随机产生？

Question

我有五个不同数字面孔的骰子。说我希望它们从（x：150，y：400）下降。我如何做到这一点，以便每次从设定位置下降不同的面对模具？是否需要for i in 0..1循环？愿意在需要时发布相关代码。先感谢您。

  class GameScene: SKScene {

   override func didMoveToView(view: SKView) {

    runAction(SKAction.repeatActionForever(
        SKAction.sequence([
            SKAction.runBlock({[unowned self] in self.falling()}),
            SKAction.waitForDuration(5.0)])))







    func falling() -> SKSpriteNode {
    let first = SKSpriteNode(imageNamed: "Dice")
    first.size = CGSizeMake(45, 45)
    first.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(45, 45))
    first.physicsBody?.dynamic = true
    first.name = "Die1"

    let positions = [
        CGPointMake(150, 600),
        CGPointMake(300, 600),
        CGPointMake(100, 600),
    ]

    let randomPositionIndex = Int(arc4random_uniform(UInt32(positions.count)))
    first.position = positions[randomPositionIndex]

    first.physicsBody?.affectedByGravity = false

       addChild(first)
    first.runAction(
        SKAction.moveByX(0, y: -900,
            duration: NSTimeInterval(10.8)))


    return first


}

}