SSK2 - Removing listeners

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#1

Sorry if this is a silly question, but it’s about the easy listener function in the display factories.

I’m going to use your example code here for ease.

local function onEnterFrame( self ) self.x = self.x + 1 if( self.x \>= right ) then self.x = right ignore( "enterFrame", self ) self.enterFrame = nil end end newCircle( nil, left, centerY, { enterFrame = onEnterFrame } )

Now obviously, when the object reaches the end the listener is removed.  What I would like to know is if the circle is hit by a bullet before it reaches the end and the circle removed using display.remove, do I have to ignore the listener first before removing the display object, or is it done automatically when the object is removed?

#2

This is not a silly question.  It is actually a common stumbling block for folks using Runtime listeners.
 
First, remember that listen is SSK2 shorthand for Runtime:addEventListener. i.e. We are talking about Runtime listeners here.
 
Second, Runtime listeners are NOT automatically removed in any situation.
 
Third, to answer your specific question…
 
SSK2 provides some ways to handle this:
 
Best Method (take advantage of finalize event):

local tmp = newCircle( nil, left, centerY, { enterFrame = onEnterFrame } ) function tmp.finalize( self ) ignore( "enterFrame", self ) end tmp:addEventListener( "finalize" )

Can also be written like this:

local function finalize( self ) -- If any of these listeners is attached to the object stop and remove them. ignoreList( { "enterFrame", "accelerometer", "onTwoTouchLeft", "myEvent" } , self ) end local tmp = newCircle( nil, left, centerY, { enterFrame = onEnterFrame, finalize = finalize } )

Second Best, use the autoIgnore() helper:

local function onEnterFrame( self ) -- Abort if the object was deleted AND remove the listener if( autoIgnore("enterFrame",self) ) then return end self.x = self.x + 1 if( self.x \>= right ) then self.x = right ignore( "enterFrame", self ) self.enterFrame = nil end end newCircle( nil, left, centerY, { enterFrame = onEnterFrame } ) 

This is a bit lazy and has a hidden cost since the code executes every frame.  Nontheless, I use this methodlogy often when I know there are only a few of these objects.

#3

There is third (more advanced) way SSK2 helps you if you have a number of Runtime and custom listeners attached to an object:

local tmp = newCircle( nil, left, centerY, { enterFrame = onEnterFrame } ) function tmp.finalize( self ) -- If any of these listeners is attached to the object stop and remove them. ignoreList( { "enterFrame", "accelerometer", "onTwoTouchLeft", "myEvent" } , self ) end tmp:addEventListener( "finalize" )

I created this helper to keep my code legible and because I’m even too lazy to do this:

local tmp = newCircle( nil, left, centerY, { enterFrame = onEnterFrame } ) function tmp.finalize( self ) ignore( "enterFrame", self ) ignore( "accelerometer", self ) ignore( "onTwoTouchLeft", self ) ignore( "myEvent", self ) end tmp:addEventListener( "finalize" )
#4

Brilliant.  Thanks Ed that clears things up for me (pun intended).

Before you go though, on a similar note, is it also necessary to remove physics bodies?

#5

Nope.  Physics bodies are removed automatically when you delete the object they are attached to.

#6

Sweet.  Thank you.

#7

This is not a silly question.  It is actually a common stumbling block for folks using Runtime listeners.
 
First, remember that listen is SSK2 shorthand for Runtime:addEventListener. i.e. We are talking about Runtime listeners here.
 
Second, Runtime listeners are NOT automatically removed in any situation.
 
Third, to answer your specific question…
 
SSK2 provides some ways to handle this:
 
Best Method (take advantage of finalize event):

local tmp = newCircle( nil, left, centerY, { enterFrame = onEnterFrame } ) function tmp.finalize( self ) ignore( "enterFrame", self ) end tmp:addEventListener( "finalize" )

Can also be written like this:

local function finalize( self ) -- If any of these listeners is attached to the object stop and remove them. ignoreList( { "enterFrame", "accelerometer", "onTwoTouchLeft", "myEvent" } , self ) end local tmp = newCircle( nil, left, centerY, { enterFrame = onEnterFrame, finalize = finalize } )

Second Best, use the autoIgnore() helper:

local function onEnterFrame( self ) -- Abort if the object was deleted AND remove the listener if( autoIgnore("enterFrame",self) ) then return end self.x = self.x + 1 if( self.x \>= right ) then self.x = right ignore( "enterFrame", self ) self.enterFrame = nil end end newCircle( nil, left, centerY, { enterFrame = onEnterFrame } ) 

This is a bit lazy and has a hidden cost since the code executes every frame.  Nontheless, I use this methodlogy often when I know there are only a few of these objects.

#8

There is third (more advanced) way SSK2 helps you if you have a number of Runtime and custom listeners attached to an object:

local tmp = newCircle( nil, left, centerY, { enterFrame = onEnterFrame } ) function tmp.finalize( self ) -- If any of these listeners is attached to the object stop and remove them. ignoreList( { "enterFrame", "accelerometer", "onTwoTouchLeft", "myEvent" } , self ) end tmp:addEventListener( "finalize" )

I created this helper to keep my code legible and because I’m even too lazy to do this:

local tmp = newCircle( nil, left, centerY, { enterFrame = onEnterFrame } ) function tmp.finalize( self ) ignore( "enterFrame", self ) ignore( "accelerometer", self ) ignore( "onTwoTouchLeft", self ) ignore( "myEvent", self ) end tmp:addEventListener( "finalize" )
#9

Brilliant.  Thanks Ed that clears things up for me (pun intended).

Before you go though, on a similar note, is it also necessary to remove physics bodies?

#10

Nope.  Physics bodies are removed automatically when you delete the object they are attached to.

#11

Sweet.  Thank you.