Help with crashing mission script

[Fisherman82]

Im using a script for setting a flag when a EWR radar detects a blue unit in a zone. 

This is the script that is used as a lua predicate on a continus trigger:

EWR1_RED_Unit = Unit.getByName('EWR_1')
if EWR1_RED_Unit ~= nil then
    EWR1_RED_Ctrl = EWR1_RED_Unit:getGroup():getController()
    local Targets = EWR1_RED_Ctrl:getDetectedTargets(VISUAL, RADAR)
    if #Targets > 0 then
        local InterestingTargets = 0
        for n = 1, #Targets do
            if Targets[n].object:isExist() == true and Targets[n].object:inAir() == true and Targets[n].object:getCoalition() == 2 then
                InterestingTargets = InterestingTargets + 1
                local TargetPosition = Targets[n].object:getPosition()
                local RedZoneInfo = trigger.misc.getZone('RedEWRzone1')
                local DistanceToRedZone = math.sqrt(math.pow(TargetPosition.p.x - RedZoneInfo.point.x, 2) + math.pow(TargetPosition.p.y - RedZoneInfo.point.y, 2))
                if DistanceToRedZone <= RedZoneInfo.radius then
                    return true
                end
            end
        end
    end
end

 

The problem is that the script sometimes crashes when a blue unit is shot down by a SAM, not every time but sometimes, seemingly randomly.

I get the error in the image.

What is the reason for the error and can I tweak the script to avoid it?

Would be most thankfull for any help

[Fisherman82]

I think its something with when the only detected blue unit is destroyed when the script is running then the n value becomes blank (nil) and then the script crashes. 

I dont know how to prevent that, any ideas?

[cfrag]

44 minutes ago, Fisherman82 said:

I think its something with when the only detected blue unit is destroyed when the script is running then the n value becomes blank (nil) and then the script crashes. 

Lets try and find out. You are doing a lot of stuff in the line: indexing, dereferencing and invoking all at once. Perhaps build in some more guards. Instead of 

 

for n = 1, #Targets do
	if Targets[n].object:isExist() == true and Targets[n].object:inAir() == true and Targets[n].object:getCoalition() == 2 then

	end
end

try 

for n = 1, #Targets do
	local theTarget = Targets[n]
	if theTarget then 
		local theObject = theTarget.object
		if theObject and theObject:isExist() and theObject:inAir() and theObject:getCoalition() == 2 then 
			--[[--
				do stuff here
			--]]--
		end
	end
end

 

[Fisherman82]

5 hours ago, cfrag said:

Lets try and find out. You are doing a lot of stuff in the line: indexing, dereferencing and invoking all at once. Perhaps build in some more guards. Instead of 

 

for n = 1, #Targets do
	if Targets[n].object:isExist() == true and Targets[n].object:inAir() == true and Targets[n].object:getCoalition() == 2 then

	end
end

try 

for n = 1, #Targets do
	local theTarget = Targets[n]
	if theTarget then 
		local theObject = theTarget.object
		if theObject and theObject:isExist() and theObject:inAir() and theObject:getCoalition() == 2 then 
			--[[--
				do stuff here
			--]]--
		end
	end
end

 

I tried this, and I think it works! 

Ran the test mission 6 times and got the only detected blue aircraft shot down with a SAM everytime without getting the script error message.

Since it used to occur randomly I cant be 100% sure that it works but 6 tests with no errors was unusual before, will test more, thank you! this script is a gamechanger!