Global Variables

I am using director and I would like to make it so if you press a button on one screen, that changes a variable to be used on another screen.

Example code that does not work because I am dumb:

Screen1.lua

module(..., package.seeall)
-- Main function - MUST return a display.newGroup()
color = 0;
function new()
        local localGroup = display.newGroup()
        
--PreStuFZ      
        -- Background
local background = display.newImage("bg.png")
localGroup:insert(background)
        --
 
        --Menu
local bt01 = display.newRect(100,150,100,50)
local function bt01t ( event )
        if event.phase == "ended" then
                director:changeScene("screen2","moveFromLeft")
        end
end
bt01:addEventListener("touch",bt01t)
bt01.x = 160
bt01.y = 200
localGroup:insert(bt01)
        --
local bt02 = display.newRect(100,50,100,50)
local function bt02t ( event )
        if event.phase == "ended" then
                color = 256;
        end
end
bt02:addEventListener("touch",bt02t)
bt02.x = 180
bt02.y = 270
localGroup:insert(bt02)
 
        -- MUST return a display.newGroup()
        return localGroup
end

local bt01 = display.newRect(100,150,100,50)
local function bt01t ( event )
if event.phase == "ended" then
_G["color"] = 0
director:changeScene("screen2","moveFromLeft")
end
end

I use this _G["color"] = 0 a lot.. but you should make it local on the next screen for speed.

I tried that and all I get is this error.

WARNING: display.setStatusBarMode() not supported in the simulator for the current device
Runtime error
        error loading module 'screen1' from file 'E:\Users\Du\Desktop\App\VarsExam\screen1.lua':
        E:\Users\Du\Desktop\App\VarsExam\screen1.lua:29: '<name>' expected
 near '['
stack traceback:
        [C]: ?
        [C]: ?
        [C]: in function 'require'
 
        Runtime error: error loading module 'screen1' from file 'E:\Users\Du\Desktop\App\VarsExam\screen1.lua':
        E:\Users\Du\Desktop\App\VarsExam\screen1.lua:29: '<name>' expected
 near '['
stack traceback:
        [C]: ?
        [C]: ?
        [C]: in function 'require'
        E:\Users\DuSchiRuntime error
        E:\Users\Du\Desktop\App\VarsExam\director.lua:135: ERROR: table expected. If this is a function call, you might have used '.' instead of ':'
stack traceback:
        [C]: ?
        [C]: in function 'insert'
        E:\Users\Du\Desktop\App\VarsExam\d

The answer to your question is very simple. Just declare a variable in main.lua, like this:

xyz = 123

This still seems to have no effect!

Main.lua

display.setStatusBar( display.HiddenStatusBar )
color = 0
 
local director = require("director")
 
local mainGroup = display.newGroup()
 
local function main()
        mainGroup:insert(director.directorView)
        director:changeScene("screen1")
        return true
end
main()

Dude, you forgot to mention what you're expecting vs. what you're getting. That's a lot of code to try to guess at it.

Button pressed changes a value on one screen. That same value sticks if it switches to another screen.

Not specific enough, sorry, I'm tired and going to bed. I'm willing to help, but I'm not going to wade through 75 lines of code to fix your problem for you when you don't even bother to define what the problem is in specific terms. Have you tried reducing the problem to something very very simple (10-20 lines), like the example I posted?

lococo: "Unless you say "local", all variables in Lua are global."

that's not actually quite true

mainmenu.lua

module(..., package.seeall)
function doSomething()
  print("dosomething in mainmenu")
  xyz=345
  _G["globalXYZ"]="DEF"
end

Yep, it looks like you're right. It seems that module(..., package.seeall) is the culprit here, which is interesting. If you define the mainmenu.lua module like this, and leave all other code untouched, it works fine:

local M = {}
function M.doSomething()
  print("dosomething in mainmenu")
  xyz=345
  _G["globalXYZ"]="DEF"
end
return M

that's not actually quite true

huh, thanks for that example. That could be what's causing the tiny memory leak I wasted hours on yesterday before giving up.

lococo, in your example where you remove "module", it's essentially the same as if you put your mainmenu code inside your main.lua. that's all require is really doing there, that's why it works

local M = {}
function M.doSomething()
  print("dosomething in mainmenu")
  xyz=345
  _G["globalXYZ"]="DEF"
end
 
local mainmenu=M
 
xyz = 123
_G["globalXYZ"]="ABC"
 
print("xyz="..xyz) -- 123
print("globalxyz=".._G["globalXYZ"]) -- ABC
 
mainmenu.doSomething()
 
print("xyz="..xyz) -- still 123
print("globalxyz=".._G["globalXYZ"]) -- DEF

One of the effects of the module function is to change the environment of the code that calls module. What that means is that any global assignments in the rest of that file go into the module table, rather than the thread environment. Using package.seeall with module allows global lookups to retrieve values from the thread global environment (which is how reference is to _G work inside a module declaration, actually), but assignments go into the module table.

This usually still means they're globally accessible. If you make a global assignment in a module "m" to the global "xyz", outside code can retrieve it as "m.xyz", because module typically creates the module table in a global variable.

Environments are one of the most confusing aspects of Lua but also among the most powerful.

views:1954 update：2011/10/6 9:28:12


Label: corona android iphone ipad building error inmobi problem display screen View image tableView failed object physics touch button game lua config event listener