DragItem.OnPointerDown C# (CSharp) Method

    public void OnPointerDown(PointerEventData data)
    {
        if (data.button == PointerEventData.InputButton.Left)
        {
            RectTransformUtility.ScreenPointToLocalPointInRectangle(rectTransform, data.position, data.pressEventCamera, out pointerOffset);
            oldSlot = transform.parent.gameObject;
        }
        if (updateInventoryList != null)
            updateInventoryList();
    }