Can't access variable in Lua

[Nadromar]

So i'm trying to write a boss script which does stuff every 5 seconds with this code:

local boss

local function handleBossFight(eventId, delay, repeats)
    if (not boss:IsInCombat() or not boss:IsAlive()) then
        return
    end
    ...
end


local function onEnterCombat(event, creature, target)
    boss = creature
    CreateLuaEvent(handleBossFight, 5000, repeats)
end


RegisterCreatureEvent(BOSSID, 1, onEnterCombat)

I'm getting the following error:
Calling 'IsInCombat' on bad self (Creature expected, got pointer to nonexisting invalidated object userdata)

Tried several other ways to access it but I just can't figure it out. :/

[Sklug]

So i'm trying to write a boss script which does stuff every 5 seconds with this code:

local boss

local function handleBossFight(eventId, delay, repeats)
    if (not boss:IsInCombat() or not boss:IsAlive()) then
        return
    end
    ...
end


local function onEnterCombat(event, creature, target)
    boss = creature
    CreateLuaEvent(handleBossFight, 5000, repeats)
end


RegisterCreatureEvent(BOSSID, 1, onEnterCombat)

I'm getting the following error:
Calling 'IsInCombat' on bad self (Creature expected, got pointer to nonexisting invalidated object userdata)

Tried several other ways to access it but I just can't figure it out. :/

I will be honest, I am not too familiar with LUA, but if you are getting that kind of error, it's typically because you are trying to call a function on an Object that has not been initialized, or does not exist. For example, let's say you call for a boolean return like the "IsInCombat" on the boss is going to produce an error if there is no boss, or you have no "target." This command is something you'd use on an existing object, so it will error if there isn't one. I think you are on the right track, but what I would probably recommend is maybe some work around, like identifying the boss first and maybe, setting the boss as a "Focus" target if it is found. This way you won't encounter errors if say, you lose the target for whatever reason, it is still your focus static target. This will help prevent lots of those types of errors. Rather than checking for the specific boss, instead you set boss as a focus target if he has been found, then instead of saying "not boss:IsInCombat()" like you did, you can first wrap it all in some like (and forgive my lack of LUA knowledge), but something like

if Me.Focus != null && Me.Focus.IsAlive() then

Again, just pseudo code but I am sure you get the idea...

Hopefully this helps and hopefully someone can correct me if I am off.

[stoneharry]

I'm assuming you are using Eluna, but either way your original post is going about this in the wrong way.

local function handleBossFight(eventID, delay, repeats, pUnit)
    if (not pUnit:IsInCombat() or not pUnit:IsAlive()) then
        pUnit:RemoveEvents()
        return
    end
    -- My boss is going to do something now
end

local function onEnterCombat(event, pUnit, target)
    -- called every 5 seconds until unit:RemoveEvents() is called
    pUnit:RegisterEvent(handleBossFight, 5000, 0)
end

RegisterCreatureEvent(BOSSID, 1, onEnterCombat)

It would be better to hook on death and leaving of combat than waiting for your function to detect the boss is no longer in combat.

As an example on how to code where something will be instanced, you can see my code for this video below: https://www.youtube.com/watch?v=7W1pZwhCGLw

-- Constants
local guardA_ID = 120001
local guardB_ID = 120002
local invisDummyID = 120003

-- Instance tables
CM = {}
CM.VAR = {}

-- Gossip start event
function CM.VAR.OnGossipHello(event, player, creature)
	player:GossipClearMenu()
	player:GossipMenuAddItem(9, "< Placeholder Menu >", 120000, 1)
	player:GossipMenuAddItem(0, "Nevermind.", 120000, 2)
	player:GossipSendMenu(120000, creature)
end

function CM.VAR.OnGossipSelect(event, player, pUnit, sender, intid, code)
	player:GossipComplete()
	if intid == 1 then
		pUnit:SetNPCFlags(0)
		CM.VAR.beginEvent(pUnit)
	end
end

RegisterCreatureGossipEvent(120000, 1, CM.VAR.OnGossipHello)
RegisterCreatureGossipEvent(120000, 2, CM.VAR.OnGossipSelect)

-- Utility
function getNearbyCreature(id, pUnit)
	if id == pUnit:GetEntry() then
		return pUnit
	end
	local creatures = pUnit:GetCreaturesInRange(20, id)
	if #creatures == 0 then
		pUnit:SendUnitSay("ERROR: creatures == 0", 0)
		return
	end
	if #creatures == 1 then
		return creatures[1]
	end
	return creatures[math.random(1, #creatures)]
end

-- Start event
function CM.VAR.beginEvent(pUnit)
	local id = pUnit:GetInstanceId() or 1
	CM[id] = CM[id] or {VAR={}}
	local guardA = getNearbyCreature(guardA_ID, pUnit)
	local guardB = getNearbyCreature(guardB_ID, pUnit)
	pUnit:SendUnitSay("The crypts are filled with the undying, we must proceed carefully.", 0)
	guardB:SetWalk(true)
	guardB:MoveTo(0, 203, 104, 128.4)
	guardA:SetWalk(true)
	guardA:MoveTo(0, 197.3, 104.57, 128.42)
	pUnit:SetWalk(true)
	pUnit:MoveTo(0, 200, 107, 128.42)
	CM[id].VAR.i = 0
	pUnit:RegisterEvent(CM.VAR.eventTicker, 1000, 0)
end

-- Event ticker
function CM.VAR.eventTicker(eventID, delay, repeats, pUnit)
	local id = pUnit:GetInstanceId() or 1
	CM[id] = CM[id] or {VAR={}}
	CM[id].VAR.i = CM[id].VAR.i + 1
	local i = CM[id].VAR.i
	if i == 5 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		guardA:SendUnitSay("We've dealt with these kind before. This should be no problem.", 0)
	elseif i == 9 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		guardA:CastSpell(guardA, 36858)
		guardB:CastSpell(guardB, 36858)
		local creature = guardA:SpawnCreature(120003, guardA:GetX(), guardA:GetY(), guardA:GetZ(), 0, 8, 10000)
		creature:SetUInt32Value(0x0006 + 0x0035, 33554432)
		creature:RegisterEvent(CM.VAR.MoveDummies, 1000, 8)
		creature = guardB:SpawnCreature(120003, guardB:GetX(), guardB:GetY(), guardB:GetZ(), 0, 8, 10000)
		creature:SetUInt32Value(0x0006 + 0x0035, 33554432)
		creature:RegisterEvent(CM.VAR.MoveDummies, 1000, 8)
	elseif i == 16 then
		for _,v in pairs(pUnit:GetCreaturesInRange(70, 120003)) do
			v:RemoveEvents()
			v:DespawnOrUnsummon(0)
		end
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		guardB:MoveTo(0, 203, 48, 128)
		guardA:MoveTo(0, 198, 47, 128)
		pUnit:MoveTo(0, 201, 51, 128)
	elseif i == 20 then
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		guardB:SendUnitSay("How have their come to be so many down here?", 0)
	elseif i == 25 then
		pUnit:SendUnitSay("There must be a necromancer. It's the only possible scenario I can think of.", 0)
	elseif i == 32 then
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		guardB:SendUnitSay("I don't like the sound of that.", 0)
	elseif i == 41 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		pUnit:MoveTo(0, 193, 49, 128)
		guardA:MoveTo(0, 193, 53, 128)
		guardB:MoveTo(0, 193, 46, 128)
	elseif i == 44 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		pUnit:MoveTo(0, 172, 49, 115)
		guardB:MoveTo(0, 172, 45, 115)
		guardA:MoveTo(0, 172, 52, 115)
	elseif i == 56 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		pUnit:MoveTo(0, 166, 42, 115)
		guardB:MoveTo(0, 170, 42, 115)
		guardA:MoveTo(0, 163, 42, 115)
	elseif i == 58 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		pUnit:MoveTo(0, 183, 22, 115)
		guardB:MoveTo(0, 186, 25, 115)
		guardA:MoveTo(0, 180, 17, 115)
	elseif i == 73 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		pUnit:SetFacing(5.518449)
		guardA:SetFacing(5.333883)
		guardB:SetFacing(5.761922)
	elseif i == 74 then
		pUnit:SendUnitYell("Necromancer, prepare to face the light for your judgement has come!", 0)
		pUnit:Emote(5)
	elseif i == 76 then
		local necro = pUnit:GetCreaturesInRange(40, 120006)[1]
		necro:RemoveEvents()
		necro:StopSpellCast(40193)
		necro:CastSpell(necro, 67040, true)
		for _,v in pairs(pUnit:GetCreaturesInRange(40, 120005)) do
			v:CastSpell(v, 40927, true)
			v:Emote(431)
		end
	elseif i == 78 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		pUnit:CastSpell(pUnit, 465, true)
		pUnit:Emote(45)
		guardA:Emote(45)
		guardB:Emote(45)
	elseif i == 81 then
		local necro = pUnit:GetCreaturesInRange(40, 120006)[1]
		necro:StopSpellCast(67040)
		for _,v in pairs(pUnit:GetCreaturesInRange(40, 120005)) do
			v:CastSpell(v, 47496, false)
		end
		pUnit:CastSpell(pUnit, 45922, true)
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		necro:SendUnitYell("You shall all perish!", 0)
		necro:SetUInt32Value(0x0006 + 0x0035, 0)
	elseif i == 87 then
		local guardA = getNearbyCreature(guardA_ID, pUnit)
		guardA:CastSpell(guardA, 45922, true)
		local guardB = getNearbyCreature(guardB_ID, pUnit)
		guardB:CastSpell(guardB, 45922, true)
	elseif i == 100 then
		pUnit:RemoveEvents()
	end
end

-- Dummy projectile killing scourge at start
function CM.VAR.MoveDummies(eventID, delay, repeats, pUnit)
	pUnit:CastSpell(pUnit, 44880, true)
	pUnit:CastSpell(pUnit, 43241, true)
	pUnit:MoveTo(0, pUnit:GetX(), pUnit:GetY() - 10, pUnit:GetZ())
	for _,v in pairs(pUnit:GetCreaturesInRange(8, 120004)) do
		v:CastSpell(v, 16003, true)
		pUnit:Kill(v)
	end
end

-- Make trash walk around randomly
function CM.VAR.FlashyTrashMoveAround(event, pUnit, ...)
	if event == 5 then -- spawned
		pUnit:SetUInt32Value(0x0006 + 0x0035, 2 + 131072)
		pUnit:SetFaction(14)
		pUnit:RegisterEvent(CM.VAR.MoveRandom_Call, math.random(100, 3000), 1)
	else
		pUnit:RemoveEvents()
	end
end

function CM.VAR.MoveRandom_Call(eventID, delay, repeats, pUnit)
	pUnit:MoveRandom(2)
	pUnit:RegisterEvent(CM.VAR.MoveRandom_Call, math.random(100, 3000), 1)
end

RegisterCreatureEvent(120004, 5, CM.VAR.FlashyTrashMoveAround)
RegisterCreatureEvent(120004, 4, CM.VAR.FlashyTrashMoveAround)


-- Prisoners

function CM.VAR.PrisonerSpawn(event, pUnit)
	pUnit:SetUInt32Value(0x0006 + 0x0035, 2 + 131072)
	if pUnit:GetEntry() == 120006 then
		pUnit:RegisterEvent(CM.VAR.StranglePeople, 3100, 0)
	else
		local maxHealth = pUnit:GetMaxHealth() / 2
		local amount = math.random(1, 10)
		if (math.random(1,2) == 1) then
			maxHealth = maxHealth + amount
		else
			maxHealth = maxHealth - amount
		end
		pUnit:SetHealth(maxHealth)
	end
end

function CM.VAR.StranglePeople(eventID, delay, repeats, pUnit)
	pUnit:StopSpellCast(40193)
	local creature = getNearbyCreature(120005, pUnit)
	if not creature then
		pUnit:SendUnitSay("ERROR: No unit found.", 0)
		return
	end
	creature:CastSpell(creature, 28136, true)
	pUnit:CastSpell(creature, 40193, true)
	creature:Emote(473)
	creature:RegisterEvent(CM.VAR.StopEmote, 3000, 1)
end

function CM.VAR.StopEmote(id, delay, repeats, pUnit)
	pUnit:Emote(20)
end

RegisterCreatureEvent(120005, 5, CM.VAR.PrisonerSpawn)
RegisterCreatureEvent(120006, 5, CM.VAR.PrisonerSpawn)
RegisterCreatureEvent(120006, 4, CM.VAR.FlashyTrashMoveAround)

It is bad practice in general to store any sort of direct reference to the object in a variable outside of the scope of the function in question. If you must determine if it is the same npc as later and it is not a unique npc ID then store the GUID and find the creature that matches the stored GUID.

You can store a player's GUID and get the object back by using:

local player = GetPlayerByGUID(playerGUID)

Which can obviously return nil.

[Nadromar]

Yeah, the script was a trainwreck :P This solved it:

hpPercent = 100
function onEnterCombat(event, creature, target)
    creature:SendUnitYell(MESSAGE_ON_START,0)
    creature:RegisterEvent(Update, 1000, 0)
    creature:RegisterEvent(Stage1, 5000, 0)
    creature:RegisterEvent(Stage2, 5000, 0)
    creature:RegisterEvent(Stage3, 5000, 0)
    creature:RegisterEvent(Stage4, 10000, 0)
end
function Update(event, delay, pCall, creature)
    hpPercent = creature:GetHealthPct()
end
function Stage1(event, delay, pCall, creature)
    if (hpPercent < 75 and not midStunActive) then
             ...
        end
end

...
local function reset(creature)
    -- reset
    creature:RemoveEvents()
    hpPercent = 100
end
function onLeaveCombat(event, creature)
    reset(creature)
end
function onDied(event, creature, killer)
    reset(creature)
end


RegisterCreatureEvent(BOSSID, 1, onEnterCombat) -- on enter combat
RegisterCreatureEvent(BOSSID, 2, onLeaveCombat) -- reset
RegisterCreatureEvent(BOSSID, 4, onDied) -- reset

[stoneharry]

Yeah, the script was a trainwreck :P This solved it:

hpPercent = 100
function onEnterCombat(event, creature, target)
    creature:SendUnitYell(MESSAGE_ON_START,0)
    creature:RegisterEvent(Update, 1000, 0)
    creature:RegisterEvent(Stage1, 5000, 0)
    creature:RegisterEvent(Stage2, 5000, 0)
    creature:RegisterEvent(Stage3, 5000, 0)
    creature:RegisterEvent(Stage4, 10000, 0)
end
function Update(event, delay, pCall, creature)
    hpPercent = creature:GetHealthPct()
end
function Stage1(event, delay, pCall, creature)
    if (hpPercent < 75 and not midStunActive) then
             ...
        end
end

...
local function reset(creature)
    -- reset
    creature:RemoveEvents()
    hpPercent = 100
end
function onLeaveCombat(event, creature)
    reset(creature)
end
function onDied(event, creature, killer)
    reset(creature)
end


RegisterCreatureEvent(BOSSID, 1, onEnterCombat) -- on enter combat
RegisterCreatureEvent(BOSSID, 2, onLeaveCombat) -- reset
RegisterCreatureEvent(BOSSID, 4, onDied) -- reset

Try to avoid global variables at all times. Here's a clean up:

local MESSAGE_ON_START = "Hello world."

local function onEnterCombat(event, creature, target)
    creature:SendUnitYell(MESSAGE_ON_START, 0)
    creature:RegisterEvent(Update, 1000, 0)
    creature:RegisterEvent(Stage1, 5000, 0)
    --[[creature:RegisterEvent(Stage2, 5000, 0)
    creature:RegisterEvent(Stage3, 5000, 0)
    creature:RegisterEvent(Stage4, 10000, 0)]]
end

function Stage1(event, delay, pCall, creature)
    if (creature:GetHealthPct() < 75 and not midStunActive) then
        ...
    end
end

local function resetCreature(event, creature, ...)
	-- ... = optional further arguments
	-- If you need to do event specific stuff, if event == 2, etc
    creature:RemoveEvents()
end


RegisterCreatureEvent(BOSSID, 1, onEnterCombat) -- on enter combat
RegisterCreatureEvent(BOSSID, 2, resetCreature) -- reset
RegisterCreatureEvent(BOSSID, 4, resetCreature) -- reset

[Nadromar]

Hmh, would a global variable not be better since GetHealthPct() gets called in every stage? In stage 4 it would call it 4 times every 5sec.
I do use global variables too much though.

[stoneharry]

Hmh, would a global variable not be better since GetHealthPct() gets called in every stage? In stage 4 it would call it 4 times every 5sec.
I do use global variables too much though.

Nah, Lua calls native C functions. That is incredibly fast. It is much better to get it each function call than attempt to store that value as a variable - memory is much more expensive. And it's just not good programming to store stuff in global variables where it can be avoided - whether that is global within your class or wherever.