Removing spawned display objects using "for loops"

Audio and Graphics
#1

In my game, I am trying to remove spawned display objects when they fall below the screen (maximumY) by using a for loop, but when I run the code it removes the first couple objects that pass maximumY, then I get a runtime error that says the objects are nil.

Thanks in advance :slight_smile:

local bounds, childGroup, spawnTimer

local spawnedObject = {}

local P = {}

local minimumX = 50

local maximumX = display.viewableContentWidth - 50

local minimumY = 50

local maximumY = display.viewableContentHeight - 50

bounds = {

     xMin = 0,

     xMax = display.viewableContentWidth,

     yMin = -300,

     yMax = -100,

     spawnTime = 500,

     spawnOnTimer = 1,

     spawnInitial = 0

}

function P.spawnItem()

comet = display.newImageRect( “comet2.png”, 150, 150 )

comet.x = math.random( bounds.xMin, bounds.xMax )

comet.y = math.random( bounds.yMin, bounds.yMax )

comet.myName = “comet” 

physics.addBody( comet, { density=1.0, bounce=0.1, radius=70, filter=cometCollisionFilter } )

comet.angularVelocity = -200

comet.gravityScale = 0.8

comet2 = display.newImageRect( “comet3.png”, 130, 130 )

comet2.x = math.random( bounds.xMin, bounds.xMax )

comet2.y = math.random( bounds.yMin, bounds.yMax )

comet2.myName = “comet2”

physics.addBody( comet2, { density=1.0, bounce=0.1, radius=60, filter=comet2CollisionFilter } )

comet2.angularVelocity = 375

comet2.gravityScale = 1.0

comet3 = display.newImageRect( “comet2.png”, 140, 140 )

comet3.x = math.random( bounds.xMin, bounds.xMax )

comet3.y = math.random( bounds.yMin, bounds.yMax )

comet3.myName = “comet3”

physics.addBody( comet3, { density=1.0, bounce=0.1, radius=65, filter=comet3CollisionFilter } )

comet3.angularVelocity = -250

comet3.gravityScale = 0.9

spawnedObject[#spawnedObject+1] = comet

spawnedObject[#spawnedObject+1] = comet2 

spawnedObject[#spawnedObject+1] = comet3 

for i = 1, #spawnedObject do

     if spawnedObject[i].y > maximumY then

          spawnedObject[i]:removeSelf()

     end

end

childGroup = display.newGroup()

childGroup:insert( comet )

childGroup:insert( comet2 )

childGroup:insert( comet3 )

sceneGroup:insert( childGroup )

end

spawnTimer = timer.performWithDelay( bounds.spawnTime, P.spawnItem, 0 )

I also tried creating a function inside P.spawnItem() over the for loop but had no luck.

#2

You are removing display items, and the spawnedObjects table then contains nil values.  In your loop, check for nil first…

[lua]

for i = 1, #spawnedObject do

    if spawnedObject[i] ~= nil then

        if spawnedObject[i].y > maximumY then

              spawnedObject[i]:removeSelf()

        end

    end

end

 

[/lua]

 

A couple of other things…

 

  1.  Those objects have physics bodies on them, so I would also “removeBody” when deleting.

 

  1.  It looks like you are creating and removing objects every 500 milliseconds.  For 3 objects, that might not be a big deal, but it will become noticeable if more objects were added.  I would reuse these objects via object pooling.  Shameless plug, but I have a blog post about using object pooling in Corona right here.

 

Hope this helps.  

#3

Still not working for me, I will give the object pooling technique a go.

Thanks for your help. 

#4

You are removing display items, and the spawnedObjects table then contains nil values.  In your loop, check for nil first…

[lua]

for i = 1, #spawnedObject do

    if spawnedObject[i] ~= nil then

        if spawnedObject[i].y > maximumY then

              spawnedObject[i]:removeSelf()

        end

    end

end

 

[/lua]

 

A couple of other things…

 

  1.  Those objects have physics bodies on them, so I would also “removeBody” when deleting.

 

  1.  It looks like you are creating and removing objects every 500 milliseconds.  For 3 objects, that might not be a big deal, but it will become noticeable if more objects were added.  I would reuse these objects via object pooling.  Shameless plug, but I have a blog post about using object pooling in Corona right here.

 

Hope this helps.  

#5

Still not working for me, I will give the object pooling technique a go.

Thanks for your help.