wpf中文本框只能输入整数

 private void txtBarCodeNum_KeyUp(object sender, KeyEventArgs e)
         {
             TxtInt(sender as TextBox);
         }

         private void txtBarCodeNum_TextChanged(object sender, TextChangedEventArgs e)
         {
             TxtInt(sender as TextBox);
         }

         private void TxtInt(TextBox txt)
         {
             if (txt==null || string.IsNullOrEmpty(txt.Text))
             {
                 txt.Tag = "";
                 return;
             }
             try
             {
                 txt.Text = txt.Text.Trim();
                 txt.Tag = Convert.ToInt32(txt.Text); ;
             }
             catch
             {
                 if (txt.Tag==null)
                 {
                     txt.Text = "";
                 }
                 else
                 {
                     txt.Text = txt.Tag.ToString();
                 }
             }
             txt.SelectionStart = txt.Text.Length;
         }