Lua OOP grid class with event

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)