Swift 如何计算显示的精灵数量？

我正在创建一个游戏，我试图让它等到显示的某个精灵的数量等于0后再继续，我尝试这样做：

NSLog("Number of asteroid 1 nodes: %d", self["Asteroid1Txt"].count)

但这会给出某个精灵的编号，即使它没有显示在屏幕上

---

有没有办法只在屏幕上显示某个精灵的编号？给精灵节点一个这样的名称：

var mySprite = SkSpriteNode(imageNamed: "nameOfYourImage")
mySprite.name = "spriteToTrack"

var countSprites = 0
enumerateChildNodesWithName(""spriteToTrack""){node,_ in
     countSprites++
     /* If you want to manipulate this node or  remove it....but dont do it in this loop! 
     let tmpNode = node as! SKSpriteNode // Must be the same as mySprite
     */
}

println("I have \(countSprites ) sprites with name spriteToTrack")

然后枚举名为“spriteToTrack”的整个精灵，如下所示：

var mySprite = SkSpriteNode(imageNamed: "nameOfYourImage")
mySprite.name = "spriteToTrack"

var countSprites = 0
enumerateChildNodesWithName(""spriteToTrack""){node,_ in
     countSprites++
     /* If you want to manipulate this node or  remove it....but dont do it in this loop! 
     let tmpNode = node as! SKSpriteNode // Must be the same as mySprite
     */
}

println("I have \(countSprites ) sprites with name spriteToTrack")