Is there something wrong with my onRelease call?

Question

Currently working on my first mobile app using the Corona simulator. I am trying to get one of my buttons to go another scene where it will display another page. Currently this is what I have

------------------main.lua-----------------
display.setStatusBar( display.HiddenStatusBar )
local storyboard = require "storyboard"
storyboard.gotoScene( "MainScreen" )

------------------MainScreen.lua------------------------
local composer = require( "composer" )
local storyboard = require ("storyboard")
local widget = require "widget"
local scene = storyboard.newScene()

local function returnStates()
        storyboard.gotoScene( "states", "crossFade", 1000 )     
    return true
end

local function returnMonth()
        storyboard.gotoScene( "months", "crossFade", 1000 )
    return true
end

----------------------------------------
function scene:createScene( event )
    local group = self.view
    local background = display.newImage( "blue.jpg" )    
     local logo = display.newImage("black.png")
            logo.x=160
            logo.y=100 
     local xor = display.newImage("or.png")
            xor.x=145
            xor.y=315

        buttonHome = widget.newButton{
            defaultFile = "statebutton.png",
            overFile = "pressedstate.png",
            onRelease = returnStates
        }
        buttonHome.x = 160
        buttonHome.y = 230



        buttonHome2 = widget.newButton{
            defaultFile = "monthbutton.png",
            overFile = "pressedmonth.png",
            onRelease = returnMonth()
        }
        buttonHome2.x = 160
        buttonHome2.y = 400

        group:insert ( background ) 
        group:insert ( buttonHome )
        group:insert ( buttonHome2 )

end
function scene:enterScene( event )
    local group = self.view    
end
function scene:exitScene( event )
    local group = self.view    
end
function scene:destroyScene( event )
    local group = self.view 
     if buttonHome then
        buttonHome:removeSelf()
        buttonHome = nil
    end     
     if buttonHome2 then
        buttonHome2:removeSelf()
        buttonHome2 = nil
    end            
end
scene:addEventListener( "createScene", scene )
scene:addEventListener( "enterScene", scene )
scene:addEventListener( "exitScene", scene )
scene:addEventListener( "destroyScene", scene )
return scene

QUESTION

I am having a hard time figuring out why I am getting this error from my Corona Simulator:

states.lua:: attempt to index global 'self' (a nil value) 
stack traceback:
[C]: in function 'error'
?: in function 'gotoScene'
MainScreen.lua:8: in function '_onRelease'
?: in function '?'
?: in function <?:677>
?: in function <?:221>

Is there something wrong with my onRelease call?

Can anyone explain to me what this means or how I can fix this?

Answer 1

Yes. The problem is the line

onRelease = returnMonth()

This line will call the returnMonth() method and put the result in the onRelease argument of the call table to widget.newButton. I cannot test it from here, but I'm pretty sure you should remove the parenthesis:

onRelease = returnMonth

Edit: Also, storyboard:gotoScene(...) – it apparently needs the self argument, and using a colon instead of dot will give it just that.