标签没有更新，因为我正在更改值

我正在编写一个小程序，根据商品数量管理商店和价格。在愿望功能中，我希望所有项目成本的总计显示在标签中。当我更改数量文本框中的值时，此标签会更新。到目前为止，我已经完成了这段代码的编写，它运行得很好，甚至变量中的值与我想要的完全相同，但问题是标签不会更新，即使我在数量文本框中有空值。它一直显示以前的总数，直到我更改值，它似乎一直停留在上次更新的总数上。

namespace wpfTest
{
    public partial class MainWindow : Window
    {
        List<int> myList = new List<int>();
        int val1, val2;
        int total;
        public MainWindow()
        {
            InitializeComponent();
        }
        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            qtyTxt1.IsEnabled = false;
            priceTxt1.IsEnabled = false;
            qtyTxt2.IsEnabled = false;
            priceTxt2.IsEnabled = false;
        }
        private void chk1_Click(object sender, RoutedEventArgs e)
        {
            if (chk1.IsChecked == true)
            {
                qtyTxt1.IsEnabled = true;
                priceTxt1.IsEnabled = true;
            }
            else
            {
                qtyTxt1.IsEnabled = false;
                priceTxt1.IsEnabled = false;
                qtyTxt1.Clear();
                priceTxt1.Text = "@50";
            }
        }
        private void chk2_Click(object sender, RoutedEventArgs e)
        {
            if (chk2.IsChecked == true)
            {
                qtyTxt2.IsEnabled = true;
                priceTxt2.IsEnabled = true;
            }
            else
            {
                qtyTxt2.IsEnabled = false;
                priceTxt2.IsEnabled = false;
                qtyTxt2.Clear();
                priceTxt2.Text = "@100";
            }
        }
        private void qtyTxt1_TextChanged(object sender, TextChangedEventArgs e)
        {
            if (qtyTxt1.Text=="")
            {
                priceTxt1.Text = "@50";
                val1 = 0;
            }
            if (qtyTxt1.Text.Length > 0)
            {
                priceTxt1.Text = (Convert.ToInt32(qtyTxt1.Text) * 50).ToString();
                val1 = Convert.ToInt32(priceTxt1.Text);
                updateTotal();
            }
        }
        private void qtyTxt2_TextChanged(object sender, TextChangedEventArgs e)
        {
            if (qtyTxt2.Text.Length == 0)
            {
                priceTxt2.Text = "@100";
                val2 = 0;
            }
            if (qtyTxt2.Text.Length > 0)
            {
                priceTxt2.Text = (Convert.ToInt32(qtyTxt2.Text) * 100).ToString();
                val2 = Convert.ToInt32(priceTxt2.Text);
                updateTotal();
            }
        }
        private void updateTotal()
        {
            lblTotal.Content = "";
            lblTotal.Content = (val1 + val2).ToString();
        }
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("Total : " + total + "'n" + "Val1 : " + val1 + "'n" + "Val2 : " + val2);
        }
    }
}

我还上传了我的Microsoft OneDrive帐户的屏幕截图，因为我在这里有上传照片的限制。：

http://1drv.ms/1lM0IdE