how to remove a not fully know event listener ?

nat12

Hello,

i have a Button class, it register all listeners for touches evens, and also users of the class add some listeners in this way

but = Button.new(main_play_bitmap, 250, 36)
but:addEventListener("clickUp", self.clickPlay, self)

later i want to use a but:destroy function to free all listeners of the button, this is easy for touches event, that were registered by button so it know all parameters, but i am unable to remove the user added listener...
i tried something similar to

if self.hasEventListener("clickUp") then
self:removeEventListener("clickUp", ?, ?)
end

but the button do not know the 2nd and 3th parameter to pass to the removeEventListener function, any suggestion?

ar2rsawseen

hello @nat12
it should be:

self:hasEventListener("clickUp")

and not

self.hasEventListener("clickUp")

use colon insetad of dot

zvardin

I was curious about this before as well. Is there any way to fetch all event listeners of a certain type on an object?

zvardin

@ar2rsawseen I think @nat12 is referring to that you need to have the function and data passed to an added event listener to remove it, but what if at the time I want to remove an event listener, I don't have a direct reference to them?

for example:

btn:addEventListener("clickUp", function() doSomething end, {foo=1,bar=2})

ar2rsawseen

haha, silly me.
Yep got it now. But unfortunately there is no way, at least I don't know one.
You need to pass exactly the same parameters to remove event listener. Same thing goes in javascript. But unless you pass the correct function, it does not know which function to remove (if for example you have multiple of them).

@nat12 how could user actually add event?

well usually you save the event handler (and all needed parameters) as property of class, like:

btn.clickUp = function() doSomething end btn.clickUpParams = {foo=1,bar=2} btn:addEventListener("clickUp", btn.clickUp, btn.clickUpParams)   -- and then to remove btn:removeEventListener("clickUp", btn.clickUp, btn.clickUpParams)

techdojo

My solution is like @ar2sawseen's - in my custom button class I have a reference to a callback function that is passed when the button is created. Then when the button is pressed the custom callback function is called so that the function that called the button know's when it's been pressed - this neatly hides all the messy lower level event "twiddling" code and leaves a nice clean high level interface, literately

local thisButtonsID = 1   local function wasPressed(button) print("Button "..button.id.." was pressed") end   myButton = CustomButton( { ... id = thisButtonsID, callback = wasPressed ... } )

Note : That's just a bit of psuedo code, when creating a custom ui control I usually pass my data in as a table - but you should get the idea.

nat12

I was hoping there was some way to read back the datas from the EventDispatcher instead to duplicate them in the button class.

I tried to code a generalization of what ar2rsawseen and techdojo suggested

function Button:addListener(type, listener, data)
table.insert(self.listenersTable, { t = type, l = listener, d = data } )
self:addEventListener(type, listener, data)
end

function Button:removeListeners()
for i = 1, #self.listenersTable do
local data = self.listenersTable[i]
self:removeEventListener(data.t, data.l, data.d)
end
end

(Atilim, if you are reading, any chance to have a removeAllListeners() function added to EventDispather in near future?)