swift - SKAction runAction 不执行完成 block

Question

SKSpriteNode 是 SKNode 的子节点，并放置在 SKSpriteNode 数组中用于存储目的。

此 SKSpriteNode 使用动画删除。在此动画结束时，执行完成 block 以执行一些语句...

删除必须同时发生在 SKSpriteNode 父节点和数组中。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 block 。
• 如果顺序相反，1/SKNode parent's then 2/the array, completion block is not executed.

为什么会这样？

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 被放置在从 theGrid 中删除操作之前，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 :

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 Action 才会运行。通过调用 removeFromParent，您可以从场景中移除节点，永远不会调用 runBlock 操作(因为节点不再存在于场景中)，因此序列永远不会完成的。由于序列未完成，因此不会调用完成 block 。

为了安全起见，我建议将 removeFromParent 调用移至完成 block 。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")
   }
}

---

长话短说
序列未完成，因此不会调用序列的完成 block 。