self.view Objects Cleanup - lua

Question

I am trying to understand how to efficiently remove scene objects once a scene is destroyed. According to corona docs objects can be inserted to self.view in order to clean them up once a scene is destroyed.
Here is my code that I am trying
local composer = require( "composer")
local scene = composer.newScene()
local rects={}
local rectsNum = 0
local rectsCount = 0
local rectsTimer
local sceneGroup
local function rectTransComplete( obj )
print("rectTransComplete .. called")
rectsCount = rectsCount + 1
if rectsCount == 3 then
composer.removeScene("scene2")
end
end
local function spawnRect( )
print("inside spawnrects")
rectsNum = rectsNum + 1
rects[rectsNum] = display.newRect( display.contentWidth/2, 100, 100, 100)
rects[rectsNum]:setFillColor( 1,1,1 )
rects[rectsNum].id = numRect
rects[rectsNum].transition = transition.to( rects[rectsNum], {time = 9000, y = display.contentHeight + 100,
onComplete = rectTransComplete
} )
sceneGroup:insert( rects[rectsNum] )
end
function scene:create( event )
sceneGroup = self.view
end
function scene:show(event)
print("inside create")
if event.phase == "did" then
rectsTimer = timer.performWithDelay( 1000, spawnRect, -1 )
end
end
function scene:hide( event )
-- body
end
function scene:destroy( event )
timer.cancel( rectsTimer )
print("scene Destroyed")
end
scene:addEventListener( "create", scene )
scene:addEventListener( "show", scene )
scene:addEventListener( "hide", scene )
scene:addEventListener( "destroy", scene )
return scene
I seems to work fine since all the rectangles are removed from the screen once the scene is destroyed but I see the app printing messages "rectTransComplete .. called" even after the scene is destroyed. Why is it so and why are the transitions not automatically cancelled once the objects are removed. Do I need to cancel all transitions manually by iterating through all the rectangles and cancel each transition. What about the rects table as it also contains references to the rects. Should I manually clean it up. If I need to manually clean everything (or most of the things), what exactly is the benefit of using self.view

Answer 1

Just a note, you will also have the same problem if you ever use Runtime events to propagate events to your display objects.
I had the same issue a few days ago, there are 2 ways to approach this:
Method 1: You keep a reference to the opened transitions, iterate through all your references and call transition.cancel(transitionReference) on them.
Method 2: You create a listener in your rectangles objects, send a runtime event to the rectangles object when the scene is destroyed that triggers the listener, and inside the listener you "cancel" the transition linked to current rectangle (transition.cancel(rectangle))
You can have a look at this article if you need a howto to work with runtime events: http://www.engelteddy.com/softwaredevelopment/mobiledevelopment/observer-pattern-corona-sdk/

Answer 2

You need to call transition.cancel() in scene:destroy function.