C# 如何获得；Guid"；ASP.NET中http头中的变量

下一行给出错误（无法将类型“string”转换为“System.Guid”）

是否有任何解决方案可以在http标头Get中传递Guid变量

try {
    userId = new Guid(Request.QueryString["id"]);
} catch (FormatException e) {
    /*
     * It's possible that the guid is not properly formatted and an
     * exception will be thrown, so handle that here.
     */
}

try {
    userId = new Guid(Request.QueryString["id"]);
} catch (FormatException e) {
    /*
     * It's possible that the guid is not properly formatted and an
     * exception will be thrown, so handle that here.
     */
}