Asp.Net后台弹出确认提示窗Confirm

前端js代码：

function MyConfirm(message, guid) {
            if (confirm(message) == true) {
                document.getElementById("Hidden1").value = guid;
            }
            else {
                document.getElementById("Hidden1").value = "";
            }
            //form1.submit();
            form1.submit();
        }

后台C#代码：

    /// <summary>
    /// 用于标识Confirm是否继续当前操作
    /// </summary>
    public string ConfirmValue
    {
        get { return ViewState["ConfirmValue"] == null ? "" : ViewState["ConfirmValue"].ToString(); }
        set { ViewState["ConfirmValue"] = value; }
    }

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!string.IsNullOrEmpty(ConfirmValue))
        {
            btnSave_Click(null, null);//后台弹出确认对话框
        }
        if (IsPostBack)
            {
                return;
            }
    }

protected void btnSave_Click(object sender, EventArgs e)
    {


        if (string.IsNullOrEmpty(ConfirmValue))//提示
                        {
                            string strGuid = Guid.NewGuid().ToString();
                            ConfirmValue = strGuid;
                            ScriptManager.RegisterStartupScript(this, this.GetType(), "_ShowMessage", "MyConfirm('是否继续？','" + strGuid + "');", true);
                            return;
                        }
                        if (!string.IsNullOrEmpty(ConfirmValue) && ConfirmValue != Hidden1.Value)//取消
                        {
                            ConfirmValue = "";
                            //ShowMessage("提示", "您取消了当前操作");
                            return;
                        }
                        else//如果点击确认，则需要把ConfirmValue初始化为空
                        {
                            ConfirmValue = "";
                        }
}