Lua OOP grid class with event - oop

Question

I'm learning lua and i'm trying the OOP approach.
To start, I'm trying to make a grid class, but I think i'm still lacking some knowledge to make it do what I want it to do.
This is my code so far:
local screen = require( 'data.screen')
Grid = {}
Grid_mt = { __index = Grid }
--- Constructs a new Grid object.
function Grid:new( params )
local self = {}
local function try( self, event )
print(self.empty)
end
for i = 1, screen.tilesAcross do
if not self[i] then
self[i] = {};
end
for j = 1, screen.tilesDown do
self[i][j] = display.newImageRect( params.group, "images/playable.png", screen.tileWidth, screen.tileHeight )
self[i][j].x = (j - 1) * (screen.tileWidth + screen.tileSpacing) + screen.leftSpacing
self[i][j].y = (i - 1) * (screen.tileHeight + screen.tileSpacing) + screen.topSpacing
self[i][j]._x = i
self[i][j]._y = j
self[i][j].enable = false
self[i][j].empty = true
self[i][j].tap = try
self[i][j]:addEventListener( "tap", self[i][j] )
end
end
setmetatable( self, Grid_mt )
return self
end
function Grid:setEnable(value, x, y)
if value ~= true and value ~= false then
error("Boolean expected")
end
self[x][y].enable = value
end
function Grid:getEnable(x, y)
return self[x][y].enable
end
function Grid:setEmpty(value, x, y)
if value ~= true and value ~= false then
error("Boolean expected")
end
self[x][y].empty = value
end
function Grid:getEmpty(x, y)
return self[x][y].empty
end
function Grid:SetmColor()
self[1][4]:setFillColor( 255,255 )
end
I have 2 questions:
My event works but I would like to do something like: print(self:getEmpty() )
but whenever I try to use a method in my event, it doesn't work "attempt to call method 'getEmpty' (a nil value)"
and also the setfillcolor wwon't work, I want to be able to change the color of a case with it.
Thanks for your time!
and if i'm going to the wrong road, let me know, and by the way, I have a working code without make a class, this is just for training purpose :)
Thnaks!

Answer 1

The issue is that self[i][j] is not a Grid, only self is a Grid. So when the event handler is called, self in the handler is the display object, not the Grid object. If the handler needs to know the grid object, you could assign the grid to each display object:
self[i][j].grid = self
then in try you could do
grid = self.grid
But in this case you may get a cleaner design if you have the tap handler not be specific to each display object. In this case you would use an upvalue, you can just use self:
function Grid:new( params )
local self = {}
local function try( event ) -- omit the first param, self is an upvalue
print(self.empty)
end
for i = 1, screen.tilesAcross do
...
for j = 1, screen.tilesDown do
self[i][j] = display.newImageRect( ... )
...
self[i][j]:addEventListener( "tap", try )
end
end
Since listener given is a function rather than a table, it gets only one parameter, the event, and self is an upvalue so it will be the Grid instance created just above the try function.

Answer 2

For the first question, more information would be needed. See my comment above.
As for the setFillColor not working, the following is taken from the Corona docs:
object:setFillColor( gray )
object:setFillColor( gray, alpha )
object:setFillColor( red, green, blue )
object:setFillColor( red, green, blue, alpha )
object:setFillColor( gradient )
gray, red, green, blue, alpha (optional)
Numbers between 0 and 1 that represent the corresponding
value for that channel. alpha represents the opacity of the object.
Now, when you are trying to execute:
self[1][4]:setFillColor( 255,255 )
you are passing the values for gray and alpha channels. The values NEED TO BE less than, or equal to 1. Probably you want to pass 1 (as 255 is generally the max. value)