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 = "";
                         }
 }