CODEWITHSUNDEEP
luacoronasdkcollision-detectionnullcorona-storyboard
Psicolabile
Psicolabile

Reputation: 41

event.other is nil in onCollision after resuming the scene with storyboard library [CORONA sdk]

I'm having a strange error developing with Corona SDK relating to collision-detection and the storyboard lib.

Here is my onCollision listener:

local function onBottomBorderCollision( event )    
    if (event.other.isBall) then
        local index = table.indexOf( ballArray, other )
        table.remove( ballArray, index )
        event.other:removeSelf( )
        event.other = nil
        updateLife(false)
        updateScore(false)
    end
end

This works fine at first launch, but after getting back to the menu screen (using storyboard.goToScene("menu")) and replaying the game, now this listener will trigger the following error every time one of my ball hits the bottom border:

attempt to index field "other"(a nil value)

I do create the proper listeners in scene:onEnterScene(scene) so it's not something to do with them, moreover this other listener never generate the error:

local function onPlayerCollision( event )


    if(event.other.isBall) then
       xVel, yVel = event.other:getLinearVelocity( )
       event.other:setLinearVelocity( event.other.XLinearVelocity, yVel )

   end

end

I am stuck right now... please help!

Upvotes: 4

Views: 325

Answers (2)

Krishna Raj Salim
Krishna Raj Salim

Reputation: 7390

Actually, this type of error is caused mainly due to to some active function call/timers/transitions, which is not yet cancelled before changing the scene.

attempt to index field "other"(a nil value)

The above error mentions that any object/ it's property is being called/fetched, but it is not in the current occurrence or the scene. So, check whether you are cancelling your timers, transitions and runtime event listeners.

In your case, it may be due to the failure in cancellation of collision detection function onBottomBorderCollision in runtime. If you are calling it in enterFrame, then you have to cancel it before scene change. YOu can do it as below:

Runtime:removeEventListener("enterFrame",onBottomBorderCollision)

Update: You can't stop the physics engine while collision check is running. So do as follows:

function actualSceneChange()
     physics.stop() -- stop physics here
     -- call scene chage
     director:changeScene("menuPageName") -- call your scene change method
end

function initiatingSceneChange()
    physics.pause() -- pause physics here
    -- stop unwanted event listeners
    Runtime:removeEventListener("enterFrame",onBottomBorderCollision) 

    if(timer_1)then timer.cancel(timer_1) end    -- stop all your timers like this.
    if(trans_1)then transition.cancel(trans) end -- stop all your transitions like this.

    timer.performWithDelay(1000,actualSceneChange,1)
end

Upvotes: 3

Hassaanz
Hassaanz

Reputation: 182

I believe the issue is because storyboard saves some variables in memory when you switch scenes. The display objects gets destroyed but the reference remains. You are probably initializing your display objects in CreateScene function which gets called only once if you do not remove your scene.

Destroying the scene in the enter scene function of menu would probably fix the issue. This is done by the Storyboard.removeScene function.

On the "EnterScene" Function of menu.lua, add in a line to remove the scene. eg. if your scene name is game:

storyboard.removeScene("game")

You can know more about difference between destroyScene and purgeScene here

Upvotes: 0

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