Lua Create multiple collisions

Question

I'm trying to create a break breaker game that contains brinks that can be hit twice before the disappear.

I have tried:

 --FOR STRONGER DEFENDERS
        for i = 1, len do
            for j = 1, level_W do
                if(level[i][j] == 2) then               
                    local strong = display.newImage('images/strongdefender.png')
                    strong.name = 'strong'
                    strong.x = def_W * j - offset
                    strong.y = def_H * i
                    physics.addBody(strong, {density = 1, friction = 0, bounce = 0})
                    strong.bodyType = 'static'
                    strongs.insert(strongs, strong)
                end
            end
        end
        for i = 1, len do
            for j = 1, level_W do
                if(level[i][j] == 2) then
                local defender = display.newImage('images/defender.png')
                    defender.name = 'defender'
                    defender.x = def_W * j - offset
                    defender.y = def_H * i
                    physics.addBody(defender, {density = 1, friction = 0, bounce = 0})
                    defender.bodyType = 'static'                    
                end
            end
        end

level is a table which is filled with 0 and 2. 2 is where the defender image will be in the game.

My collision event is like so:

function onCollision(e)


        if(e.other.name == 'defender' or e.other.name == 'strong' and (ball.x + ball.width * 0.5) < (e.other.x + e.other.width * 0.5)) then
            xSpeed = -5
        elseif(e.other.name == 'defender' or e.other.name == 'strong' and (ball.x + ball.width * 0.5) >= (e.other.x + e.other.width * 0.5)) then
            xSpeed = 5
        end

        if(e.other.name == 'defender') then
            audio.play(defencePop)
            ySpeed = ySpeed * -1
            e.other:removeSelf()
            e.other = nil
            defenders.numChildren = defenders.numChildren - 1

            --SORT SCORE
            score = score + 1
            scoreNum.text = score * points
            scoreNum:setReferencePoint(display.CenterLeftReferencePoint)
            scoreNum.x = 54 
        elseif(e.other.name == 'strong') then
            audio.play(defencePop)
            ySpeed = ySpeed * -1
            e.other:removeSelf()
            e.other = nil
            defenders.numChildren = defenders.numChildren - 1

            --SORT SCORE
            score = score + 1
            scoreNum.text = score * points
            scoreNum:setReferencePoint(display.CenterLeftReferencePoint)
            scoreNum.x = 54     

        end




        --defenders.numChildren < 0
        if(strongs.numChildren < 0) then
            bgAlert('win')
            gameStatus = 'win'
        end
    end -- removeDefender

When the ball collides with the element, both of them disappear. How can I make one disappear at a time?

Answer 1

I would suggest you just put the strong on the screen and add an event listener to them the weaker brick is created when the collision occurs with the stronger brick. The idea is to remove the object and add a new one when the collision occurs.
First you would display the strong object and add them to physics. You would also add a local collision event listener to the object

 for i = 1, len do
     for j = 1, level_W do
         if(level[i][j] == 2) then               
             local strong = display.newImage('images/strongdefender.png')
             strong.name = 'strong'
             strong.x = def_W * j - offset
             strong.y = def_H * i
             physics.addBody(strong, {density = 1, friction = 0, bounce = 0})
             strong.bodyType = 'static'
             strong.collision = onBrickCollision --onStrongCollision is the name of the collision handler function
             strong:addEventListener("collision" , strong) --add collision listener
             strongs.insert(strongs, strong)
         end
     end 
 end

The event listener would be like

function onBrickCollision(self , event)
if event.phase == "began" and event.other.name == "ball" then
    if (ball.x + ball.width * 0.5) < (self.x + self.width * 0.5) then
        xSpeed = -5
    else
        xSpeed = 5
    end
    if self.name == "strong" then
        audio.play(defencePop)
        ySpeed = ySpeed * -1
        --Create defender on the position of strong and add it to physics
        local defender = display.newImage('images/defender.png')
        defender.name = 'defender'
        set the position same as the object which is hit by ball
        defender.x = self.x
        defender.y = self.y
        physics.addBody(defender, {density = 1, friction = 0, bounce = 0})
        defender.bodyType = 'static'
        defender.collision = onBrickCollision
        defender:addEventListener("collision", defender)
        --remove the strong brick
        self:removeSelf()
        self = nil

        --SORT SCORE
        score = score + 1
        scoreNum.text = score * points
        scoreNum:setReferencePoint(display.CenterLeftReferencePoint)
        scoreNum.x = 54     

    elseif self.name == "defender" then
        audio.play(defencePop)
        ySpeed = ySpeed * -1
        self:removeSelf()
        self = nil
        defenders.numChildren = defenders.numChildren - 1

        --SORT SCORE
        score = score + 1
        scoreNum.text = score * points
        scoreNum:setReferencePoint(display.CenterLeftReferencePoint)
        scoreNum.x = 54 
    end
end

Hope the code is self explanatory :)
Feel free to ask me if you have any further questions.