private void HideLettersOnCard(WordCard wordCard)
		{
			switch (Window.InputDevice)
			{
				case InputDevice.Mouse : 
				{
					wordCard.LettersThatAreShown = LettersThatAreShown.FirstCharacter;
					break;
				}
				case InputDevice.Keyboard :
				{
					wordCard.LettersThatAreShown = LettersThatAreShown.Nothing;
					break;
				}
				default :
				{
					throw new ApplicationException("never reach here.");
				}
			}
		}
 private void Shuffle()
 {
     var queue = new Queue<MondaiWord>(正位置を避けるシャッフル(Ankimon.GetMondaiWords()));
     foreach (var ankimonRowContainer in _ankimonBox.Items.Cast<AnkimonRowContainer>())
     {
         var collection = ankimonRowContainer.WordCardContainer.Items;
         for (int i = 0; i < collection.Count(); i++)
         {
             collection[i] = new WordCard(queue.Dequeue());
         }
     }
 }