For循环在swift似乎随机选择增量

Question

我有一个for循环执行动画，然后完成删除它们，我试图在完成时调用另一个方法。这是我的代码：

func animateMatch(completion:() ->()) { 
    var movingShape = level.shapeAtColumn(pointsContainingShapeArray[0].Column, row: pointsContainingShapeArray[0].Row) 
    let destinationShape = level.shapeAtColumn(pointsContainingShapeArray[0].Column, row: pointsContainingShapeArray[0].Row) 

    for everyShape in 1..<pointsContainingShapeArray.count { 
     movingShape = level.shapeAtColumn(pointsContainingShapeArray[everyShape].Column, row: pointsContainingShapeArray[everyShape].Row) 

     let Duration: NSTimeInterval = 1 

     let moveShapes = SKAction.moveTo((destinationShape?.sprite!.position)!,duration: Duration) 
     moveShapes.timingMode = .EaseOut 

     movingShape?.sprite?.runAction(moveShapes, completion: { 
      movingShape?.sprite?.removeFromParent() 
      print("Removed shape \(everyShape)") 
      if everyShape == pointsContainingShapeArray.count { 
       completion() 
      } 
     }) 

    } 
} 

基本上这个想法是，所述第一位置之后的阵列中的每个的形状移动到第一个的位置，然后从场景中删除。这工作正常，但我的完成每次都随机调用。所以最后我在那里添加了打印语句。这里是输出：

Removed shape 3 
Removed shape 1 
Removed shape 4 
Removed shape 2 

在这一点上，我非常沮丧，我决定是时候堆栈溢出。我无法弄清楚这里发生了什么。谢谢你的帮助！

这里是调用此方法的代码：

func handleSwipe(move: Move) { 
    view.userInteractionEnabled = false 

    level.performMove(move) 

    scene.animateMove(move) { 
     self.view.userInteractionEnabled = true 
     if hasMatch { 
      self.view.userInteractionEnabled = false 

      self.scene.animateMatch() { 
       self.scene.addNewSpritesForShapes(pointsContainingShapeArray) 
       hasMatch = false 
       self.view!.userInteractionEnabled = true 

      } 

     } 

    } 

} 

Answer 1

问题不在于for循环，它的运行动作的异步特性。

当您调用moveShapes操作时，它在异步调用完成回原线程之前运行。这可以以任何顺序发生。您可以通过调用同步打印看到自己：

for everyShape in 1..<pointsContainingShapeArray.count { 
    print("Synchronous loop: \(everyShape)") 
} 

我想你会更好使用dispatch_group_t你最终完成：

func animateMatch(completion:() ->()) { 
    var movingShape = level.shapeAtColumn(pointsContainingShapeArray[0].Column, row: pointsContainingShapeArray[0].Row) 
    let destinationShape = level.shapeAtColumn(pointsContainingShapeArray[0].Column, row: pointsContainingShapeArray[0].Row) 
    // HERE 
    let group = dispatch_group_create() 
    dispatch_group_notify(group, dispatch_get_main_queue(), completion) 
    // 
    for everyShape in 1..<pointsContainingShapeArray.count { 
     // HERE 
     dispatch_group_enter(group) 
     // 
     movingShape = level.shapeAtColumn(pointsContainingShapeArray[everyShape].Column, row: pointsContainingShapeArray[everyShape].Row) 

     let Duration: NSTimeInterval = 1 

     let moveShapes = SKAction.moveTo((destinationShape?.sprite!.position)!,duration: Duration) 
     moveShapes.timingMode = .EaseOut 

     movingShape?.sprite?.runAction(moveShapes, completion: { 
      movingShape?.sprite?.removeFromParent() 
      print("Removed shape \(everyShape)") 
      // HERE 
      dispatch_group_leave(group) 
      // 
     }) 

    } 
}