For循環在swift似乎隨機選擇增量

Question

我有一個for循環執行動畫，然後完成刪除它們，我試圖在完成時調用另一個方法。這是我的代碼：

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() 
      } 
     }) 

    } 
} 

基本上這個想法是，所述第一位置之後的陣列中的每個的形狀移動到第一個的位置，然後從場景中刪除。這工作正常，但我的完成每次都隨機調用。所以最後我在那裏添加了打印語句。這裏是輸出：

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

在這一點上，我非常沮喪，我決定是時候堆棧溢出。我無法弄清楚這裏發生了什麼。謝謝你的幫助！

這裏是調用此方法的代碼：

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

問題不在於for循環，它的運行動作的異步特性。

當您調用moveShapes操作時，它在異步調用完成回原線程之前運行。這可以以任何順序發生。您可以通過調用同步打印看到自己：

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

我想你會更好使用dispatch_group_t你最終完成：

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) 
      // 
     }) 

    } 
}