Swift：SKNode intersectsNode无效

Question

以下代码无法按预期工作。因为我无法理解的原因“怪物交叉玩家”从未被称为。这是怎么回事？

            for monsterNode in self.children as [SKNode]{
                if (monsterNode.name? == "monster") {
                    println("monster node found")
                    for playerNode in self.children as [SKNode]{
                        if (playerNode.name? == "player"){
                            println("player found")
                            if(monsterNode.intersectsNode(playerNode)){
                                println("monster intersects player")
                            }
                        }
                    }
                }
            }

对于玩家节点与怪物节点相交的一个玩家节点和三个怪物节点，将打印以下内容：

monster node found
player found
monster node found
player found
monster node found
player found