SKAction runAction 不执行完成块

Question

A SKSpriteNode 是 SKNode 的子项，出于存储目的放置在 SKSpriteNode 的数组中。

这个SKSpriteNode是用动画删除的。在此动画结束时，执行完成块以执行一些语句...

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

如果从 1/ 数组中删除 SKSpriteNode，然后从 SKNode 父数组中删除 2/，则执行完成块。
if inverse order, 1/ SKNode parent's then 2/ the array, completion block不执行。

为什么会出现这种行为？

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removeFromParent放在remove from theGrid动作之前，如下，补全不执行：

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：

An SKAction object is an action that is executed by a node in the scene (SKScene)...When the scene processes its nodes, actions associated with those nodes are evaluated.

换句话说，当且仅当该节点在场景中时，该节点的动作是运行。通过调用 removeFromParent，您从场景中移除节点，永远不会调用 runBlock 动作（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")
   }
}

TL;DR
序列未完成，因此未调用序列的完成块。

SKAction runAction 不执行完成块

SKAction runAction does not execute completion block

sprite-kit

swift