SKAction runAction 不执行完成块

Question

SKSpriteNode 是 SKNode 的子代，并且出于存储目的放置在 SKSpriteNode 的数组中。

这个SKSpriteNode 使用动画删除。在这个动画的最后会执行一个完成块来执行一些语句......

删除必须同时发生在 SKSpriteNode 父级和数组中。根据这 2 次删除的顺序，结果是否正确：

• 如果 SKSpriteNode 从数组 1/ 中删除，然后从 SKNode 父数组中删除 2/，则执行完成块。
• 如果逆序，1/ SKNode parent 的 then 2/ 数组，完成块不被执行。

为什么会有这种行为？

for position in listOfPositions {

   theSprite:SKSpriteNode = theGrid[position]

   /// the SKSpriteNode referenced by theSprite :
   /// - belongs to an array of SKSpriteNode: theGrid
   /// - belongs to a SKNode: theGameLayer
   ///
   /// In other words this SKSpriteNode is referenced twice
   ///

   let theActions = SKAction.sequence([
      /// Some actions here
      /// ...

      /// Remove theSprite from the Grid
      /// - position is an instance of a structure of my own
      /// - theGrid is accessed via a subscript
      ///
      SKAction.runBlock({self.theGrid[position] = nil}),

      /// remove theSprite from it's parent
      SKAction.removeFromParent(),
   ])

   theSprite.runAction(theActions,completion:{NSLog("Deleted")})
}

显示完成消息。

现在如果将removeFromParent 放在remove from theGrid 操作之前，如下所示，完成不会执行：

let theActions = SKAction.sequence([
   /// Some actions here
   /// ...

   /// remove theSprite from it's parent
   SKAction.removeFromParent(),

   /// remove theSprite from the Grid
   SKAction.runBlock({self.theGrid[position] = nil}),
])

Answer 1

来自SKAction Reference：

SKAction 对象是由节点执行的动作 场景（SKScene）...当场景处理其节点时，与这些节点相关的动作 节点被评估。

换句话说，当且仅当该节点在场景中时，该节点的动作才会运行。通过调用removeFromParent，您将节点从场景中移除，runBlock 动作永远不会被调用（因为节点不再在场景中），因此序列永远不会完成。由于序列未完成，因此不会调用完成块。

为了安全起见，我建议将 removeFromParent 调用移至完成块。这样的事情感觉更安全：

for position in listOfPositions {

   let theSprite: SKSpriteNode = theGrid[position]

   /// the SKSpriteNode referenced by theSprite :
   /// - belongs to an array of SKSpriteNode: theGrid
   /// - belongs to a SKNode: theGameLayer
   ///
   /// In other words this SKSpriteNode is referenced twice
   ///

   let theActions = SKAction.sequence([
      /// Some actions here
      /// ...

      /// Remove theSprite from the Grid
      /// - position is an instance of a structure of my own
      /// - theGrid is accessed via a subscript
      ///
      SKAction.runBlock({self.theGrid[position] = nil})
   ])

   theSprite.runAction(theActions) {
      /// remove theSprite from it's parent
      /// Might need to weakly reference self here
      theSprite.removeFromParent(),
      NSLog("Deleted")
   }
}

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TL;DR
序列未完成，因此不会调用序列的完成块。