help with removing an event listener

Solar2D General Questions/Discussion
#1

Hi,

I am using composer and the middle class library.

I have the following class

local Character = class('Character') function Character:initialize(view, params) self.\_view = view self:AddEventListeners() end function Character:FlyEvent(event) print('fly') end function Character:DestroyEvent(event) self:RemoveEventListeners() end function Character:AddEventListeners() self.\_view:addEventListener("screenTouched", function(e) self:FlyEvent(e) end) end function Character:RemoveEventListeners() self.\_view:removeEventListener("screenTouched", function(e) self:FlyEvent(e) end) end return Character

i am creating a character object trhough the composer scene:create

the issue I am having is that the RemoveEventListners method is fired, but it doesn’t remove the eventlistner

any ideas? thoughts?

#2

You are creating an anonymous function in addEventListener and removeEventListener thus this functions to Lua are two different functions. Try setting the function to a local variable (global in module) and using that or set a table listener on you object. Something like this:

function listener:

local function flyEvent(event) Character:FlyEvent(event) end function Character:AddEventListeners() self.\_view:addEventListener("screenTouched", flyEvent) end function Character:RemoveEventListeners() self.\_view:removeEventListener("screenTouched", flyEvent) end

table listener:

function Character:screenTouched(event) self:FlyEvent(event) end function Character:AddEventListeners() self.\_view:addEventListener("screenTouched", self) end function Character:RemoveEventListeners() self.\_view:removeEventListener("screenTouched", self) end

Code not checked. Check for errors or typos.

#3

 

primoz.cerar,

Thanks for that, makes sense… so does that mean for things like collisions as well can I do the same? As it is a Corona generated event?

function Character:AddEventListeners() self.\_view:addEventListener("collision", self) end

or do I need to do that differently?

#4

If you have function Character:collision declared then yes you can do that.

#5

primoz,

Interestingly when I do the following

 self.\_character:addEventListener("collision", function(e) self:CollisionHandler(e) end )

and then remove with 

 self.\_character:removeEventListener("collision", function(e) self:CollisionHandler(e) end )

that works… how is that possible? shouldn’t this have the same issue as the others?

my function is

function Character:CollisionHandler(event) //code end
#6

That should not work. Are you sure the addEventListener actually does anything?

I don’t know the structure of your objects.

In the above code I don’t know what self is or what self._character is.

By the code you wrote I’m guessing self is a Character instance.

What is self._character? I don’t see you setting it anywhere.

#7

Primoz,

yeah it def works… as anytime the character collides it prints out, also when i call the remove listener it stops the collision events

the  which is what confused me

yeah self is a character instance

self._character is the actual sprite instance

 self.\_character = display.newSprite(self.\_view, imageSheet , sequenceData )
#8

Then I don’t know how this can work. It should not work.

You must be a magician :slight_smile:

#9

i don’t like being a magician… :frowning:

#10

Primoz,

question for you

if I have the following method in my class

function Character:CollisionHandler(event) ..... end

How can I use a table listener to attach that to a collision event?

function Character:AddEventListeners() self.\_view:addEventListener("collision", self) --???? what would I put here? end

Thanks

#11

Every time you want to make a table listener, the table has to have a method with the same name as the event. In this case you would have to call it function Character:collision(event). Then it will work with the addEventListener line you have now.

#12

You are creating an anonymous function in addEventListener and removeEventListener thus this functions to Lua are two different functions. Try setting the function to a local variable (global in module) and using that or set a table listener on you object. Something like this:

function listener:

local function flyEvent(event) Character:FlyEvent(event) end function Character:AddEventListeners() self.\_view:addEventListener("screenTouched", flyEvent) end function Character:RemoveEventListeners() self.\_view:removeEventListener("screenTouched", flyEvent) end

table listener:

function Character:screenTouched(event) self:FlyEvent(event) end function Character:AddEventListeners() self.\_view:addEventListener("screenTouched", self) end function Character:RemoveEventListeners() self.\_view:removeEventListener("screenTouched", self) end

Code not checked. Check for errors or typos.

#13

 

primoz.cerar,

Thanks for that, makes sense… so does that mean for things like collisions as well can I do the same? As it is a Corona generated event?

function Character:AddEventListeners() self.\_view:addEventListener("collision", self) end

or do I need to do that differently?

#14

If you have function Character:collision declared then yes you can do that.

#15

primoz,

Interestingly when I do the following

 self.\_character:addEventListener("collision", function(e) self:CollisionHandler(e) end )

and then remove with 

 self.\_character:removeEventListener("collision", function(e) self:CollisionHandler(e) end )

that works… how is that possible? shouldn’t this have the same issue as the others?

my function is

function Character:CollisionHandler(event) //code end
#16

That should not work. Are you sure the addEventListener actually does anything?

I don’t know the structure of your objects.

In the above code I don’t know what self is or what self._character is.

By the code you wrote I’m guessing self is a Character instance.

What is self._character? I don’t see you setting it anywhere.

#17

Primoz,

yeah it def works… as anytime the character collides it prints out, also when i call the remove listener it stops the collision events

the  which is what confused me

yeah self is a character instance

self._character is the actual sprite instance

 self.\_character = display.newSprite(self.\_view, imageSheet , sequenceData )
#18

Then I don’t know how this can work. It should not work.

You must be a magician :slight_smile:

#19

i don’t like being a magician… :frowning:

#20

Primoz,

question for you

if I have the following method in my class

function Character:CollisionHandler(event) ..... end

How can I use a table listener to attach that to a collision event?

function Character:AddEventListeners() self.\_view:addEventListener("collision", self) --???? what would I put here? end

Thanks