public void AddItem()
        {
            var newItem = new ItemAddBall(4);

            items.Add(newItem);
            newItem.Parent = this;
        }
 public void AddItems(IEnumerable <int> cols)
 {
     foreach (var col in cols)
     {
         var newItem = new ItemAddBall(col);
         items.Add(newItem);
         newItem.Parent = this;
     }
 }