collisions with images in classes corona sdk

Question

How do I test for collisions in main.lua in corona sdk when the objects to test for are defined in another class? I have an image in player class, and an image in enemy class. In main how do I detect if these images collide?

local function onGlobalCollision (event)

if ( event.phase == "began" ) then

print( "began: " .. event.object1.myName .. " & " .. event.object2.myName )

end

end

Runtime:addEventListener( "collision", onGlobalCollision )

Answer 1

It really comes down to how you've setup your classes. You might need to post more of your code. I've created this example which works as expected:

box.lua

local Box = {}
local physics = require("physics")

function Box:new()

    local box = display.newRect(math.random(0,display.contentWidth),math.random(0,display.contentHeight),100,100)
    physics.addBody(box)

    local function onTouch(event)
        if(event.phase == "began") then
            display.getCurrentStage():setFocus(event.target)
        elseif(event.phase == "moved") then
            event.target.x = event.x
            event.target.y = event.y
        elseif(event.phase == "ended") then
            display.getCurrentStage():setFocus(nil)
        end
    end

    box:addEventListener("touch", onTouch)

    return box

end

return Box

main.lua

local physics = require("physics")
physics:start()
physics.setGravity(0,0)

local box1 = require("box"):new()
box1.myName = "box 1"

local box2 = require("box"):new()
box2.myName = "box 2"

local function onGlobalCollision (event)
    if ( event.phase == "began" ) then
        print( "began: " .. event.object1.myName .. " & " .. event.object2.myName )
    end
end

Runtime:addEventListener( "collision", onGlobalCollision )

I'm pretty sure you could even remove the stuff from main altogether. Make sure you have called physics.start() before anything else.