protected void btnOk_Click(object sender, EventArgs e)
        {
            Category oldCategory = (Category)Session["OLDCATEGORY"];

            Category newCategory = new Category();

            newCategory.Name = txtCity.Text;

            if (Session["EDITMODE"] == null || !(bool)Session["EDITMODE"])
            {
                client.AddCategory(newCategory);
            }
            else
            {
                client.ModifyCategory(oldCategory, newCategory);
                Session["EDITMODE"]    = false;
                Session["OLDCATEGORY"] = null;
            }

            txtCity.Text    = "";
            pnlCity.Visible = false;

            Response.Redirect(Request.RawUrl);
        }