Nil error from Runtime:EventListener after removing object

Getting Started Newbie Questions
#1

Hi

I call a function move(event) from Runtime:addEventListener( “enterFrame”, move );

All works well until I remove the object “plant1” as a result of a collision, then I get  nil error from the move function, even though I am checking if plant1 != nil ?

error : Attempt to perform arithmetic on field ‘x’ (a nil value)

collision event.

plant1[event.target] = nil 

event.target:removeSelf()  

move function

local function move(event)

local tDelta = event.time - tPrevious

tPrevious = event.time

if plant1 ~= null then

  plant1.x = plant1.x - xOffset

end

end

#2

if plant1 ~= nil then

#3

old habits, still errors

if plant1 ~= nil

attempt to perform arithmetic on field ‘x’ (a nil value)

stack traceback:

#4

Can you copy/paste your code.  Make sure to put it inside and (take out the spaces).

Also post your full stack trace.  It wasn’t listed above.

Rob

#5 
local function myCollisionPlant(self, event)  if  event.phase == "began"  then   if event.target.type ==  "badPlant" and event.other.type == "bird" then  lifeCount = lifeCount - 1  displayLifeCount.text = "Lifes: " .. lifeCount  audio.play(losePoint, {channel = audio.findFreeChannel()});  event.target:removeSelf()    plant1[event.target] = nil         -- We remove object from table  display.getCurrentStage():setFocus(nil) end  elseif (event.phase == "ended") then end end   function kick1(event) ----- plant   plant1 = display.newSprite(sheet2, { name="cat4", start=1, count=22, time=2000} )  plant1.xScale = -1;   plant1.y = baseline -25  plant1.x = \_W+50--\_W+150; plant1.y = baseline -2  physics.addBody(plant1, "kinematic",{density=0, friction=0, bounce=0, radius=40})   plant1.type = "badPlant"  plant1:play()   plant1.collision = myCollisionPlant  plant1:addEventListener("collision", plant1)  plant1.isSensor = true end   function scene:createScene( event     group = scene.view;     bird = display.newImage(group,"bird1.png",10)     bird.x = 200     bird.y =  centerY/3   --random(\_H2) -500 --\* .5     bird.type = "bird"    physics.addBody( bird ,"dynamic", { density=1.0, friction=1, bounce=0, radius=20})     bird.isFixedRotation=true end   function scene:enterScene( event )  group = self.view  timer1 = timer.performWithDelay( math.random(5000,6000), kick1,-1) --plant end   tPrevious = system.getTimer() local function move(event) local tDelta = event.time - tPrevious tPrevious = event.time  local xOffset = ( 0.2 \* tDelta ) if plant1 ~= nil then  plant1.x = plant1.x - xOffset end   end   -- Start everything moving Runtime:addEventListener( "enterFrame", move );
#6

Try changing
plant1[event.target] = nil
to
event.target = nil

The comment says “we remove object from table” but as far as I can tell plant1 is a display object name not a table name.

#7

As a side note, every time your timer runs it overwrites the previous plant1. If you are not destroying plant1 before the next one is generated, you’re creating a memory leak.

#8

if plant1 ~= nil then

#9

old habits, still errors

if plant1 ~= nil

attempt to perform arithmetic on field ‘x’ (a nil value)

stack traceback:

#10

Can you copy/paste your code.  Make sure to put it inside and (take out the spaces).

Also post your full stack trace.  It wasn’t listed above.

Rob

#11 
local function myCollisionPlant(self, event)  if  event.phase == "began"  then   if event.target.type ==  "badPlant" and event.other.type == "bird" then  lifeCount = lifeCount - 1  displayLifeCount.text = "Lifes: " .. lifeCount  audio.play(losePoint, {channel = audio.findFreeChannel()});  event.target:removeSelf()    plant1[event.target] = nil         -- We remove object from table  display.getCurrentStage():setFocus(nil) end  elseif (event.phase == "ended") then end end   function kick1(event) ----- plant   plant1 = display.newSprite(sheet2, { name="cat4", start=1, count=22, time=2000} )  plant1.xScale = -1;   plant1.y = baseline -25  plant1.x = \_W+50--\_W+150; plant1.y = baseline -2  physics.addBody(plant1, "kinematic",{density=0, friction=0, bounce=0, radius=40})   plant1.type = "badPlant"  plant1:play()   plant1.collision = myCollisionPlant  plant1:addEventListener("collision", plant1)  plant1.isSensor = true end   function scene:createScene( event     group = scene.view;     bird = display.newImage(group,"bird1.png",10)     bird.x = 200     bird.y =  centerY/3   --random(\_H2) -500 --\* .5     bird.type = "bird"    physics.addBody( bird ,"dynamic", { density=1.0, friction=1, bounce=0, radius=20})     bird.isFixedRotation=true end   function scene:enterScene( event )  group = self.view  timer1 = timer.performWithDelay( math.random(5000,6000), kick1,-1) --plant end   tPrevious = system.getTimer() local function move(event) local tDelta = event.time - tPrevious tPrevious = event.time  local xOffset = ( 0.2 \* tDelta ) if plant1 ~= nil then  plant1.x = plant1.x - xOffset end   end   -- Start everything moving Runtime:addEventListener( "enterFrame", move );
#12

Try changing
plant1[event.target] = nil
to
event.target = nil

The comment says “we remove object from table” but as far as I can tell plant1 is a display object name not a table name.

#13

As a side note, every time your timer runs it overwrites the previous plant1. If you are not destroying plant1 before the next one is generated, you’re creating a memory leak.