将SKEmitter添加到SKnode

Question

当我尝试将SKEmitter添加到我的节点时，由于某种原因，我得到了一个断点。谁能解释这样做的正确方法？

我的代码：

  func didBegin(_ contact: SKPhysicsContact) {

    let bodyA = contact.bodyA
    let bodyB = contact.bodyB


    if bodyA.categoryBitMask == 1 && bodyB.categoryBitMask == 2 || bodyB.categoryBitMask == 1 && bodyA.categoryBitMask == 2  {
        let player = SKNode(fileNamed: "player")
        let explostion = SKEmitterNode(fileNamed: "explosion.sks")
        explostion?.position = (player?.position)!
        self.addChild(explostion!)

    }

}