How to remove an anonymous event listener?

Question

So I've run across a problem that has been addressed in other languages but not in Corona/Lua. How does one remove an event listener with an anonymous function?

It would seem that one is supposed to 'store a reference to the function' but I'm not sure of the syntax for that in Lua. I've spent some time looking it up, and the closest match I could find was this answer, which isn't very helpful to me, being in Javascript and all.

Do you intend to have the listener remove itself? If not, how do you know when you've got the right listener? — lins314159, Aug 23 '11 at 00:05

score 3 · Accepted Answer · answered Aug 23 '11 at 17:40

Lua has no such thing as "remove event listener". This is handled by libraries/frameworks that use event listeners, in your case Corona. I have no experience with Corona, but have you looked at removeEventListener() documentation?

It seems you just need to save the reference to your listener to be able to remove it later. That is, instead of doing this:

Runtime:addEventListener( "enterFrame", function() ... end )
-- cannot remove the listener, because you have no reference to it

Do this:

-- store a reference to your listener, so that you can remove it
-- equivalent to: local handler; handler = function() ... end
local function handler() Runtime:removeEventListener("enterFrame", handler) end
Runtime:addEventListener( "enterFrame", handler )

Thanks for the answer. I gave you a plus for putting it in English. :) — Elliot Bonneville, Aug 24 '11 at 03:59

score 0 · Answer 2 · answered Aug 29 '13 at 09:42

0

sorry, above answer is nonsense! do it like this:

local function xyz() blabla end

--or

local xyz = function() blabla end

--add listener

Runtime:addEventListener('enterFrame', xyz)

--remove it again

Runtime:removeEventListener('enterFrame', xyz)

answered Aug 29 '13 at 09:42

johannes_lalala

561
4
12

score 0 · Answer 3 · answered Aug 23 '11 at 12:43

Storing the reference to a function is exactly the same as storing a reference to a variable. In order to manipulate an object later you need to give it a name, right? Well, the same goes for functions.

Incidentally, this is only an issue when using a function as the listener. However there's another style of doing event listeners, where you use a table as the listener and then have a function in the table named after the event: http://developer.anscamobile.com/content/application-programming-guide-event-handling#Listeners_and_Event_Delivery

I generally prefer using table listeners.

How to remove an anonymous event listener?

3 Answers3