Event Listener attributes

aditya

Have a lua file and a declared Core.class in it.

pScreen = Core.class(Sprite)

Now when I do this, I get "attempt to index field '?' (a nil value)"

1) function pScreen:backButtonClicked(data,event) 2) self.backButton:addEventListener(Event.MOUSE_UP, self.backButtonClicked,{self.backButton})

But this works

1) function backButtonClicked(data,event) 2) self.backButton:addEventListener(Event.MOUSE_UP, backButtonClicked,{self.backButton})

Why?

ar2rsawseen

The problem is, that:

function pScreen:backButtonClicked(data,event)

is actually a

function pScreen.backButtonClicked(self, data,event)

and when you add it as

self.backButton:addEventListener(Event.MOUSE_UP, self.backButtonClicked,{self.backButton})

what it receives is:

function pScreen.backButtonClicked({self.backButton},event)

while it expects:

function pScreen.backButtonClicked(self, data, event)

So to make it work, you should do:

--1) function pScreen:backButtonClicked(event) --self.backButton was clicked end   --2) some where in other method self.backButton:addEventListener(Event.MOUSE_UP, self.backButtonClicked,self)

Hope that helps

aditya

Got it. Thanks!

aditya

Am still a tad confused. Sorry again.

Using your solution and event:getTarget() works. But how do you pass external data in the addEventListener above?

ar2rsawseen

@aditya you don't, you simple make it as a property of a class, like this:

function MyClass:init() self.custom = "myCustom data" self:addEventListener(Event.MOUSE_UP, self.onMouseUp, self) end   function MyClass:onMouseUp(e) if self:hitTestPoint(e.x, e.y) then print(self.custom) -- prints myCustom data end end

aditya

Question, if a function is declared as pScreen.backButtonClicked instead of pScreen:backButtonClicked, will the scenemanager still be able to dereference it if the scene is changed?

ar2rsawseen

You can think of it as a static function and yes it could be referenced even if the scene was changed, cause it would actually work without any instance.
And in this case, what ever you pass to the adEventListener as a third argument will be received in this function as first, for example:

function MyClass:init() self.custom = "myCustom data" self:addEventListener(Event.MOUSE_UP, self.onMouseUp, self) end   function MyClass.onMouseUp(self, e) if self:hitTestPoint(e.x, e.y) then print(self.custom) -- prints myCustom data --but only because we passed instance as argument, not because it is a part of the class end end

So you could actually make it work with any instance, even from completely other class, by passing reference to instance like this

aditya

Okay.