How can I cast the parent of the target of an event as a class object that I have previously defined?

mutatron · July 17, 2013, 3:51am

I’m using the little class.lua found here to make a solar system with planets. All the bodies in the solar system are of the Body class, and I make an array of bodies to hold all the bodies in the system. Each body has an id, and as long as I’m using the bodies as themselves, I can get the id and do something with it, like treating the Sun as a special case.

Each body is represented visually by Corona display.newCircle(), and I add an event listener for “touch” events to each of those. Then when I’m in the onTouch function, I can get the parent of the circle like this:

&nbsp; &nbsp; local function onTouch( event ) &nbsp; &nbsp; &nbsp; &nbsp; local t = event.target &nbsp; &nbsp; &nbsp; &nbsp; local phase = event.phase &nbsp; &nbsp; &nbsp; &nbsp; if "began" == phase then &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; local parent = t.parent &nbsp;

Looking at the table id’s I’ve verified that the parent of the target is indeed the table of the Body object. What I want to do is get parent.id, so I can know which body I’m dealing with, but the “id” attribute only exists for Body objects. So the question is, how can I cast event.target.parent as a Body object so I can access its attributes and methods?

** Nevermind, the parent of a newCircle is display, so it wouldn’t work the way I wanted it to anyway.

torbenratzlaff · July 19, 2013, 10:18pm

I’m not sure I understood what you want, but the only thing you have to do is reference the body object with the graphic object. An easy way to do so, is to create them both as one object.

[LUA]

local planet = {}

local body = display.newCircle(…)

physics.addBody(planet_body, … )

planet.body = body

body.super = planet

local graphic = display.newCircle(…)

local planet.graphic = graphic

graphic.super = planet

function graphic:touch(event)

local phase = event.phase

local planet = self.super

if phase =“began” then

planet:explode() – or whatever you wanne do

end

graphic:addEventListener(“touch”)

[/LUA]

mutatron · July 20, 2013, 3:31am

Excellent! Thanks a bunch, I didn’t know I could add a .super attribute, but I guess that goes with the way lua tables work. In my function that initializes the display.newCircle I do this:

&nbsp; &nbsp; self.Orb = display.newCircle(group, 0, 0, self.orbR) &nbsp; &nbsp; self.Orb.super = self

Then the onTouch function looks like this:

&nbsp; &nbsp; local function onTouch( event ) &nbsp; &nbsp; &nbsp; &nbsp; local t = event.target &nbsp; &nbsp; &nbsp; &nbsp; local phase = event.phase &nbsp; &nbsp; &nbsp; &nbsp; if "began" == phase then &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; editingBody = t.super &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; editingBody:drawInfo(editingText)&nbsp;

Then there’s a Body class function that looks like this:

function Body:drawInfo(editingText) &nbsp; &nbsp; editingText:setTextColor(self.red, self.green, self.blue, 192) &nbsp; &nbsp; editingText.x = display.contentWidth - 100 &nbsp; &nbsp; editingText.y = 10+3\*25 &nbsp; &nbsp; editingText.text = string.format("ID &nbsp; &nbsp; &nbsp; %2d\nmass %6.2f\nVx &nbsp; %6.2f\nVy &nbsp; %6.2f",self.id, self.mass, self.V.x, self.V.y) end

Works like a charm and takes less code than what I was doing.

torbenratzlaff · July 19, 2013, 10:18pm