public string GetCallbackResult()
        {
            if (applyHistoryID > 0)
            {
                var ah = ClubLogic.GetApplyHistory(applyHistoryID);
                if (ah != null && ah.IsAccepted == null)
                {
                    var count = ClubLogic.GetClubMemberCount(ClubID);
                    var quota = ClubLogic.GetClubMemberQuota(ClubID);

                    if (!approved)
                    {
                        UserClubLogic.ApproveJoinClub(ah.ID.Value, approved, username);
                        return("false");
                    }
                    if (approved && count >= quota)
                    {
                        return(string.Empty);
                    }

                    UserClubLogic.ApproveJoinClub(ah.ID.Value, approved, username);

                    //check if user joined clubs count has reached max count, if true, cancel all applications of this user
                    var myClubs = ClubLogic.GetActiveUserClubs(userid);
                    if (myClubs.Count >= ConfigGlobal.SingleUserMaxClubCount)
                    {
                        //cancel
                        var applications = ClubLogic.GetActiveUserApplications(ah.Userid);

                        foreach (var apply in applications)
                        {
                            UserClubLogic.ApproveJoinClub(apply.ID.Value, false, ClubSysPrivateMessage.ClubSysAdminName);
                        }
                    }

                    return("true");
                }
                return(string.Empty);
            }
            return(string.Empty);
        }