How to kill a monster to level up

Generally speaking, it means one object dead when the object's HP is 0. The code shows below:

m_pKernelModule->AddPropertyCallBack( self, NFrame::NPC::HP(), this, &NFNPCRefreshModule::OnObjectHPEvent );

int NFNPCRefreshModule::OnObjectHPEvent( const NFGUID& self, const std::string& strPropertyName, const NFData& oldVar, const NFData& newVar)
{
    if ( newVar.GetInt() <= 0 )
    {
        const NFGUID& identAttacker = m_pKernelModule->GetPropertyObject( self, NFrame::NPC::LastAttacker());
        if (!identAttacker.IsNull())
		{
			OnObjectBeKilled(self, identAttacker);

			m_pScheduleModule->AddSchedule( self, "OnNPCDeadDestroyHeart", this, &NFNPCRefreshModule::OnNPCDeadDestroyHeart, 5.0f, 1 );
        }
    }

    return 0;
}

int NFNPCRefreshModule::OnObjectBeKilled( const NFGUID& self, const NFGUID& killer )
{
	if ( m_pKernelModule->GetObject(killer) )
	{
		//must player
		NF_SHARE_PTR<NFIRecord> xDropItemList = m_pKernelModule->FindRecord(killer, NFrame::Player::DropItemList::ThisName());
		if (xDropItemList)
		{
			const int64_t nExp = m_pKernelModule->GetPropertyInt( self, NFrame::NPC::EXP() );
			const int64_t nGold = m_pKernelModule->GetPropertyInt( self, NFrame::NPC::Gold() );
			const int64_t nDiamond = m_pKernelModule->GetPropertyInt( self, NFrame::NPC::Diamond() );

			m_pLevelModule->AddExp(killer, nExp);
			m_pPropertyModule->AddGold(killer, nGold);
			m_pPropertyModule->AddDiamond(killer, nDiamond);

			//add drop off item
			const int64_t nDropProbability = m_pKernelModule->GetPropertyInt(self, NFrame::NPC::DropProbability());
			const int64_t nRan = m_pKernelModule->Random(0, 100);
			if (nRan > nDropProbability)
			{
				return 0;
			}

			NF_SHARE_PTR<NFDataList> xRowData = xDropItemList->GetInitData();
			const std::string& strDropPackList = m_pKernelModule->GetPropertyString(self, NFrame::NPC::DropPackList());
			const NFVector3 vPos = m_pKernelModule->GetPropertyVector3(self, NFrame::NPC::Position());

			NFDataList xItemList;
			xItemList.Split(strDropPackList, ",");

			for (int i = 0; i < xItemList.GetCount(); ++i)
			{
				const std::string& strItem = xItemList.String(i);

				xRowData->SetObject(NFrame::Player::DropItemList::GUID, m_pKernelModule->CreateGUID());
				xRowData->SetString(NFrame::Player::DropItemList::ConfigID, strItem);
				xRowData->SetInt(NFrame::Player::DropItemList::ItemCount, 1);
				xRowData->SetVector3(NFrame::Player::DropItemList::Postion, vPos);

				xDropItemList->AddRow(-1, *xRowData);

				m_pLogModule->LogNormal(NFILogModule::NLL_INFO_NORMAL, killer, "Add Exp for kill monster", nExp);
			}
		}
		else
		{
			m_pLogModule->LogObject(NFILogModule::NLL_ERROR_NORMAL, killer, "There is no object", __FUNCTION__, __LINE__);
		}

	}

	return 0;
}