attempt to index global 'playButton' (a nil value) - lua

Question

I have just started a LUA a few weeks ago. I was able to create a simple character jumping with a score and then running this with the Corona Simulator. But I wanted to create a menu system so from main.lua which loads up menu.lua and from here it will go to Start (i.e. start the game i.e. to game.lua) and therefore I can play the game. But it doesn't appear. I have tried to add the eventListeners as shown below o
function scene:show( event )
local sceneGroup = self.view
local phase = event.phase
if ( phase == "will" ) then
-- Code here runs when the scene is still off screen (but is about to come on screen)
elseif ( phase == "did" ) then
-- Code here runs when the scene is entirely on screen
startButton:addEventListener( "tap", gotoGame )
highScoresButton:addEventListener( "tap", gotoHighScores )
end
end
Other than that I dont understand why the menu system won't go to Game.lua therefore I can play the game. Also I don't understand why there are errors when loading menu.lua I have used scenes and the composer management library and in theory it should work.
Image files are in one folder
main.lua File 1
local composer = require( "composer" )
-- Hide status bar
display.setStatusBar( display.HiddenStatusBar )
-- Seed the random number generator
math.randomseed( os.time() )
-- Go to the menu screen
composer.gotoScene("menu")
Menu.lua File 2
local composer = require( "composer" )
local scene = composer.newScene()
-- -----------------------------------------------------------------------------------
-- Code outside of the scene event functions below will only be executed ONCE unless
-- the scene is removed entirely (not recycled) via "composer.removeScene()"
-- -----------------------------------------------------------------------------------
local function gotoGame()
composer.gotoScene( "game" )
end
local function gotoHighScores()
composer.gotoScene( "highscores" )
end
-- -----------------------------------------------------------------------------------
-- Scene event functions
-- -----------------------------------------------------------------------------------
-- create()
function scene:create( event )
local sceneGroup = self.view
-- Code here runs when the scene is first created but has not yet appeared on screen
local background = display.newImageRect( sceneGroup, "background.png", 800, 1400 )
background.x = display.contentCenterX
background.y = display.contentCenterY
local title = display.newImageRect( sceneGroup, "title.png", 500, 80 )
title.x = display.contentCenterX
title.y = 200
local startButton = display.newText( sceneGroup, "Start", display.contentCenterX, 700, native.systemFont, 44 )
startButton:setFillColor( 0.82, 0.86, 1 )
local highScoresButton = display.newText( sceneGroup, "High Scores", display.contentCenterX, 810, native.systemFont, 44 )
highScoresButton:setFillColor( 0.75, 0.78, 1 )
startButton:addEventListener( "tap", gotoGame )
highScoresButton:addEventListener( "tap", gotoHighScores )
end
-- show()
function scene:show( event )
local sceneGroup = self.view
local phase = event.phase
if ( phase == "will" ) then
-- Code here runs when the scene is still off screen (but is about to come on screen)
elseif ( phase == "did" ) then
-- Code here runs when the scene is entirely on screen
startButton:addEventListener( "tap", gotoGame )
highScoresButton:addEventListener( "tap", gotoHighScores )
end
end
-- hide()
function scene:hide( event )
local sceneGroup = self.view
local phase = event.phase
if ( phase == "will" ) then
-- Code here runs when the scene is on screen (but is about to go off screen)
elseif ( phase == "did" ) then
-- Code here runs immediately after the scene goes entirely off screen
end
end
-- destroy()
function scene:destroy( event )
local sceneGroup = self.view
-- Code here runs prior to the removal of scene's view
end
-- -----------------------------------------------------------------------------------
-- Scene event function listeners
-- -----------------------------------------------------------------------------------
scene:addEventListener( "create", scene )
scene:addEventListener( "show", scene )
scene:addEventListener( "hide", scene )
scene:addEventListener( "destroy", scene )
-- -----------------------------------------------------------------------------------
return scene
game.lua File 3
local composer = require("composer")
local scene = composer.newScene()
display.setStatusBar(display.HiddenStatusBar)
local physics = require "physics"
function updateScore()
score=score+1
scoreText.text = "Score: "..score
scoreText.x, scoreText.y=80,40
end
function onTouch(event)
if(event.phase=="began") then
if(event.x<player.x) then
player:setLinearVelocity(-30,-200)
updateScore()
else
player:setLinearVelocity(30,-200)
updateScore()
end
end
end
-- create()
function scene:create( event )
local sceneGroup = self.view
-- Code here runs when the scene is first created but has not yet appeared
physics.pause()
score=0
local scoreText
local ground = display.newImage("ground.jpg")
local player = display.newImage("player.png")
end
-- show()
function scene:show( event )
local sceneGroup = self.view
local phase = event.phase
if ( phase == "will" ) then
-- Code here runs when the scene is still off screen (but is about to come on screen)
elseif ( phase == "did" ) then
-- Code here runs when the scene is entirely on screen
physics.start()
scoreText=display.newText("Score:0",0,0,native.systemFont,40)
scoreText.x, scoreText.y=80,40
ground.x=460
ground.y=1300
physics.addBody(ground, "static")
player.x=360
player.y=120
physics.addBody(player)
Runtime:addEventListener("touch", onTouch)
end
end
-- hide()
function scene:hide( event )
local sceneGroup = self.view
local phase = event.phase
if ( phase == "will" ) then
-- Code here runs when the scene is on screen (but is about to go off screen)
elseif ( phase == "did" ) then
-- Code here runs immediately after the scene goes entirely off screen
end
end
-- destroy()
function scene:destroy( event )
local sceneGroup = self.view
-- Code here runs prior to the removal of scene's view
end
-- -----------------------------------------------------------------------------------
-- Scene event function listeners
-- -----------------------------------------------------------------------------------
scene:addEventListener( "create", scene )
scene:addEventListener( "show", scene )
scene:addEventListener( "hide", scene )
scene:addEventListener( "destroy", scene )
-- -----------------------------------------------------------------------------------
return scene

Answer 1

When you create the scene with
function scene:create( event )
You always want to insert the objects (locals) into the sceneGroup doing this
sceneGroup:insert( object )
sceneGroup:insert( object2 )
Also I have the doubt that the event listener goes with touch and not tap (by looking on the doumentation):
startButton:addEventListener( "touch", gotoGame )
highScoresButton:addEventListener( "touch", gotoHighScores )
Anyway I suggest you to visit the documentation: it covers everything and it's euxhastive.