Functions in event listeners...

christopher.burkhous · January 28, 2014, 1:58am

So here’s the deal. I am trying to run a function inside of an event listener as such:

&nbsp;&nbsp;&nbsp;&nbsp;local addBtnStart = function () &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;btnStartGame = display.newText( "Start Game", 0, 0, "Helvetica", 60 ) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;btnStartGame.x = display.contentCenterX &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;btnStartGame.y = display.contentCenterY-200 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;btnStartGame.alpha=0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;transition.to( btnStartGame, {time=1000, alpha=1, y=display.contentCenterY, x=display.contentCenterX } ) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;btnStartGame:addEventListener ( "tap", woof() ) &nbsp;&nbsp;&nbsp;&nbsp;end &nbsp;

Well, woof() causes errors. As a global function waaay up top I have…

local function woof() audio.play( sndWoof ) end

HOWEVER, if I change the event listener to…

 btnStartGame:addEventListener ( "tap", woof )

AND change the function woof into a function inside a variable as such…

local woof = function() audio.play( sndWoof ) end

It works! What have I stumbled upon? What is the difference between a function and a function inside a variable? Why will a function inside a variable work in an event listener, but an actual function will NOT work in such an instance? The error I get when trying to run a function is attached as an image.

I’m new to the concept of a function inside of a variable, but it seems I can add say…

local woof = function( var1 )

or multiple in-values. What’s the difference between a function inside of a variable and an actual function? Why are they treated differently in my code (why does one work and the other doesn’t)?

Thanks!

-Chris

test567 · January 29, 2014, 1:38am

woof is the function, whereever you write woof, there will be an “uncalled” function - that is - a kind of pointer to the function

woof() calls the functions, wherever you write woof(), there will only be the return value(s) of the function, nothing else

so

btnStartGame:addEventListener ( “tap”, woof ) is correct

btnStartGame:addEventListener ( “tap”, woof() ) is wrong (as long as woof doesn’t return yet another function)

local function woof()

is just another way to write

local woof = function()

see here http://www.lua.org/pil/6.html where it says “syntactic sugar”

christopher.burkhous · January 29, 2014, 3:47am

I figured they were the same. I also found out that yea, woof calls the function woof. I didn’t realize this at the time lol. The main problem I had in addition to this was say passing variables through the function, so…

btnStartGame:addEventListener ( “tap”, woof( var1, var2 )

Only to realize that you end up doing something like this…

(another piece of my code)

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;label = "Back to menu", &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;onEvent = function( obj ) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;buttonHit( obj, "page\_menu", "slideRight") &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;end

So much to learn, I’m having fun with it (: Thanks for the help!

-Chris

test567 · January 29, 2014, 1:38am

woof is the function, whereever you write woof, there will be an “uncalled” function - that is - a kind of pointer to the function

woof() calls the functions, wherever you write woof(), there will only be the return value(s) of the function, nothing else

so

btnStartGame:addEventListener ( “tap”, woof ) is correct

btnStartGame:addEventListener ( “tap”, woof() ) is wrong (as long as woof doesn’t return yet another function)

local function woof()

is just another way to write

local woof = function()

see here http://www.lua.org/pil/6.html where it says “syntactic sugar”

christopher.burkhous · January 29, 2014, 3:47am

I figured they were the same. I also found out that yea, woof calls the function woof. I didn’t realize this at the time lol. The main problem I had in addition to this was say passing variables through the function, so…

btnStartGame:addEventListener ( “tap”, woof( var1, var2 )

Only to realize that you end up doing something like this…

(another piece of my code)

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;label = "Back to menu", &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;onEvent = function( obj ) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;buttonHit( obj, "page\_menu", "slideRight") &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;end

So much to learn, I’m having fun with it (: Thanks for the help!

-Chris