private void bt_selectedToAvailable_Click(object sender, RoutedEventArgs e)
        {
            if (dg_currentProductAndQuantity.SelectedIndex == -1)
            {
                return;
            }


            KeyValuePair <string, string> selectedItem = (KeyValuePair <string, string>)dg_currentProductAndQuantity.SelectedItem;

            string quantity;
            bool   Exists = _AllProductsAndQuantity.TryGetValue(selectedItem.Key, out quantity);

            if (!Exists)
            {
                quantity = selectedItem.Value;
            }


            ListBoxProductsAndQuantityAvailable.Add(selectedItem.Key, quantity);

            DataGridSelectedProductsAndQuantity.Remove(selectedItem.Key);

            UpdateSources();
        }
        private void bt_add_Click(object sender, RoutedEventArgs e)
        {
            if (string.IsNullOrEmpty(tb_productName.Text))
            {
                return;
            }

            int Quantity;

            if (!int.TryParse(tb_Quantity.Text, out Quantity))
            {
                return;
            }

            string oldQuantity;
            bool   exist = DataGridSelectedProductsAndQuantity.TryGetValue(tb_productName.Text, out oldQuantity);

            if (exist)
            {
                DataGridSelectedProductsAndQuantity[tb_productName.Text] = Quantity.ToString();
            }
            else
            {
                DataGridSelectedProductsAndQuantity.Add(tb_productName.Text, Quantity.ToString());
            }


            UpdateSources();
        }
        private void bt_availableToSelected_Click(object sender, RoutedEventArgs e)
        {
            if (lb_list.SelectedIndex == -1)
            {
                return;
            }

            string selectedItem = (string)lb_list.SelectedItem;

            string quantity = ListBoxProductsAndQuantityAvailable[selectedItem];

            DataGridSelectedProductsAndQuantity.Add(selectedItem, quantity);

            ListBoxProductsAndQuantityAvailable.Remove(selectedItem);

            UpdateSources();
        }