destroyBody

peach303

Hi,

i want to delete an Object completely after some time. When the object collides it changes its image. After 2 secounds it should be deleted. My first attempt is this:

function Trigger:init(xp, yp, world)   -- self:addChild(sprite) ...   local body = world:createBody{type = b2.DYNAMIC_BODY}   self.body.type = "Trigger" self.parent = self -- ..... self.body.aktiviert = false self.body.killed = false   self.body:setLinearDamping(damping)   self:addEventListener(Event.ENTER_FRAME, function() triggerAktiviert(self,world) end) end     function triggerAktiviert(self, world) if self.body.aktiviert and self.body.killed == false then if self.triggerSpr1 then self:removeChild(self.triggerSpr1) end self:addChild(self.triggerSpr2) self.triggerSpr2:setPosition(-50,-50) self.body.killed = true Timer.delayedCall(2000, function() finishHim(self,world) end) end end   function finishHim(self,world) print("killing") if self.body then world:destroyBody(self.body) end if self.triggerSpr2 then self:removeChild(self.triggerSpr2) end end

This gives an error message: body allready destroyed in this function:

function Scene3:onEnterFrame() self.world:step(1/60, 8, 3) for i = 1, self:getNumChildren() do local sprite = self:getChildAt(i) if sprite.body then -- <<<<<-------- local body = sprite.body local bodyX, bodyY = body:getPosition() sprite:setPosition(bodyX, bodyY) sprite:setRotation(body:getAngle() * 180 / math.pi) end end end

Am I right, that this error appears, because finishHim and Scene3:onEnterFrame are running parallel? And immidiately after if sprite.body (true) is checked the body gets destroyed in finishHim?

So the only way to do it is to delete the body in Scene3:onEnterFrame. if self.killed destroyBody and so on?

I just want to understand

ar2rsawseen

Am I right, that this error appears, because finishHim and Scene3:onEnterFrame are running parallel? And immidiately after if sprite.body (true) is checked the body gets destroyed in finishHim?

Yes basically you are right. First thing to do inside finishHim function is to

self.body = nil self:removeFromParent()

That way this sprite won't be looped in Scene3:onEnterFrame() and it will not try to move the body

peach303

hm this does not work:

trigger.lua:39: attempt to index field 'body' (a nil value)

It occures in function triggerAktiviert


But let me ask again: Do these functions really run parallel? Because if so, then body could get deleted after the other function checked if sprite.body then...

ar2rsawseen

no not really in paralel, but mixed. One complete function, then other complete function

And what is on trigger.lua:39?

peach303

if self.body.aktiviert and self.body.killed == false then

i tried to remove the EventListener that calls the function but still the same error?!

zvardin

So, sounds like you have code firing after the body has been set to nil. You can either check for self.body or check your code execution and maybe that code shouldn't be firing on it in the first place once destroyed.

OZApps

@peach303,
one small thing

self:addEventListener(Event.ENTER_FRAME, function() triggerAktiviert(self,world) end)

this shows a bit of the beer sdk hangover, i.e. concept from the beer sdk being used in Gideros.

With Gideros you can use some cool things and also pass data if you so wish.

so you could have the same as

function Trigger:triggerAktiviert() ... end

and set it in the addEventHandler as

self:addEventListener(Event.ENTER_FRAME, Trigger.triggerAktiviert self) end

which would pass the object self to the function

you can also pass the world, and other data if you pass the same as a table like

self.addEventListener(Event.ENTER_FRAME, Trigger.triggerAktiviert, {self, world} )

just thought you could benefit from that in case you were unaware of the same.

peach303

I just can't get this run I tried around a lot but nothing works. I attached my complete trigger.lua. When i run this an error occures immidiately after simulator start:


trigger.lua:38: attempt to index field 'body' (a nil value)
stack traceback:
trigger.lua:38: in function

Trigger = Core.class(Sprite)     local triggerTex = Texture.new("trigger.png") local triggerReg1 = TextureRegion.new(triggerTex,0,0,100,100) local triggerReg2 = TextureRegion.new(triggerTex,100,0,100,100)     function Trigger:init(xp, yp, world) self.triggerSpr1 = Bitmap.new(triggerReg1) self.triggerSpr2 = Bitmap.new(triggerReg2)   self:addChild(self.triggerSpr1) self.triggerSpr1:setPosition(-50,-50)   self:setPosition(xp,yp)   local body = world:createBody{type = b2.DYNAMIC_BODY} body:setPosition(xp, yp) body:setAngle(self:getRotation() * math.pi/180) local circle = b2.CircleShape.new(0, 0, 50) local fixture = body:createFixture{shape = circle, density = 20.0, friction = 0, restitution = 0.2} self.body = body self.body.type = "Trigger" self.parent = self   self.body.aktiviert = false self.body.killed = false   self.body:setLinearDamping(damping)   self:addEventListener(Event.ENTER_FRAME, Trigger.triggerAktiviert, {self,world} )   end     function Trigger:triggerAktiviert(self, world) if self.body.aktiviert and self.body.killed == false then --< ERROR (line 38...) if self.triggerSpr1 then self:removeChild(self.triggerSpr1) end self:addChild(self.triggerSpr2) self.triggerSpr2:setPosition(-50,-50) self.body.killed = true self.Timer.delayedCall(2000, Trigger.finishHim, {self,world}) end end   function Trigger:finishHim(self,world) print("killing") --self.body = nil --self:removeFromParent() if self.body then world:destroyBody(self.body) end if self.triggerSpr2 then self:removeChild(self.triggerSpr2) end end

zvardin

At the top of your triggerAktiviert function add this :

If not self.body then return end

That should prevent errors but tjere are probably cleaner ways to handle elsewhere in your code (like whatever calls that function most likely)

OZApps

@peach303, when working with functions and passing tables, you need to take care of that.

object.function1({self, world, "test"})   function object:function1(param) end

The param is the variable that receives the table with the data and they can be accessed as param[1], param[2], etc or have named parameters like so,

object:function({obj=self, box2dObj=world, text="test"})

and these can then be accessed as param.obj, param.box2dObj and param.text

twisttap

WHat are you trying to check on that line 38 with :
if self.body.aktiviert and self.body.killed == false then
I am just guessing but if you are trying to use the and like & I think they do not work the same way like some other languages.

zvardin

When you have functions with a colon, self is automatically handled by Lua also. In this case you need to pass more than just self, so I would take note of what @OZApps just mentioned for parameters as well.

peach303

Hi,

thx for the help. It is still not running. This prints out a "nil". I dont get it...

function Trigger:init(xp, yp, world)   --blah blah   self:addEventListener(Event.ENTER_FRAME, Trigger.triggerAktiviert, {self, world} )   return Trigger end     function Trigger:triggerAktiviert(param) print(param[1]) end

ar2rsawseen

I don't know about parameters, but what I would do, as I mentioned before somewhere on the other thread:

function Trigger:init(xp, yp, world) self.world = world --blah blah   self:addEventListener(Event.ENTER_FRAME, Trigger.triggerAktiviert, self)   return Trigger end     function Trigger:triggerAktiviert() print(self.world) end

this way you can use class properties self.property etc in any class method

zvardin

You need to change your function definition to:

function Trigger.triggerAktiviert(param) print(param[1]) end

By having the colon, you are having lua automatically assume you are getting self. I suspect what's happening is, if you checked self inside that function you would have the data you passed (self and world inside).

zvardin

@ar2sawseen's suggestion might make things a lot simpler for you also. That distinction for function definitions is important to keep in mind though.

peach303

Ok. I will change the code like ar2sawseen suggested.

But your hint workes too zvardin.

zvardin

Object = Core.class()   function Object:init()   end   function Object:test1(param) print("self is: ", self, ", param is: ", param) end   function Object.test2(self, param) print("self is: ", self, ", param is: ", param) end

The 2 functions 'test1' and 'test2' in the code above function the same. It's a handy feature in Lua, but can trip you up when learning. The colon is just short hand for not having to add self as the first parameter. The same can be said when calling a function, like so:

local x = Object.new() local p = 1 x:test1(p) x.test1(x,p) x:test2(p) x.test2(x,p)

Hope this helps!

peach303

Yes it does! It works now. Thx a lot.